Single Photon Emission Computed Tomography (SPECT) is now commonly used for quantitative imaging (QI), as such the results from SPECT based measurements should be reported with a quantitative indication of the quality of the result. In this study a novel methodology to construct a measurement model for a clinical SPECT system based on List Mode data is presented. Input probability density functions (PDFs) are determined for all calibrations and corrections applied to the system, and a Monte Carlo method for propagation of probability distributions is used to assess measurement uncertainty. The methodology is applied to estimate the uncertainties of quantitative measurements using phantoms filled with 99mTc. Details of the PDF for the List Mode data events and correction tables applied within the commercial system software are presented. The effect of correlated corrections on the uncertainty of reconstructed SPECT images is evaluated for the first time. The potential for this development to allow rigorous uncertainty budgets to be developed for SPECT based clinical procedures is discussed.

INTRODUCTION:The use of in-house developed software as a medical device (IHD-SaMD) is core to many nuclear medicine (NM) services in the UK, including applications in nonimaging studies and image processing. Expected regulatory changes in 2025 could have significant implications due to a lack of resources and expertise in the implementation and maintenance of software Quality Management Systems (QMS) and associated standards. This survey investigated the national use of IHD-SaMD and the readiness of services to adapt to the upcoming regulatory changes. METHOD:An online survey was used to investigate the current national usage of IHD-SaMD. Representatives of 64 UK NM physics services were invited to participate, with 43 responding. RESULTS:It was found that 98% of respondents use IHD-SaMD clinically. About 65% use IHD-SaMD that respondents felt was under-supported (e.g. legacy software). Approximately 60% of respondents use or support two or more pieces of IHD-SaMD. Around 66% of respondents use a QMS in their department, with about 48% using a software-specific QMS. Most respondents indicate understaffing, particularly with regard to IT/software skillsets. Almost all respondents indicate without an increase in the preparedness and understanding of the requirements, all dependent clinical services would be severely impacted or indeed stopped. CONCLUSION:This national survey shows that pending regulatory changes could significantly impact NM services, up to and including stopping clinical services. Additional resources would be required to support in-house software management under an appropriate QMS or move to European conformity marking (CE)-marked software where available. This must be urgently considered and addressed by all NM stakeholders.

Introduction In nuclear medicine, medical physicists play a key role together with doctors, radiographers, technologists, nurses, radiopharmacists and other support staff in delivering a safe, efficacious and efficient clinical service. The role of the nuclear medicine physicist is well-defined in many publications [1–5] and typically focuses on the following areas: Optimisation of diagnostic and therapeutic techniques. Patient radiation safety. Equipment acceptance testing and quality assurance. Investigation and recommendations following patient radiation incidents. Safety and radiation dosimetry of radionuclide therapies. As with many staff groups in healthcare, there is a hierarchy within the medical physics profession. In the UK, trainee physicists commonly enter the profession via the NHS Scientific Training Programme or via an equivalence route. Upon completion of accredited training and achieving a master's degree, medical physicists are eligible to apply for Registration with the Health and Care Professions Council (HCPC) as Clinical Scientists. However, in addition to this basic grade in medical physics, there is the legally defined role of the medical physics expert (MPE). These individuals have enhanced skills and responsibilities typically formed following several years of experience post-registration. The requirement for employers to have input from MPEs was given in the original Ionising Radiation (Medical Exposure) Regulations (IR(ME)R) 2000, although their responsibilities were sparsely defined, with guidance suggesting someone with several years' experience would be qualified for the role. However, in the revised regulations IR(ME)R 2017, the definition of the MPE was expanded and clarified with clear areas of responsibility. Furthermore, a requirement for these individuals to be on a statutory register was introduced, with registrants obliged to submit and be assessed on a portfolio of evidence according to a well-defined list of competencies [6]. To facilitate transition, allowance was made at the time of the introduction of IR(ME)R 2017 for existing MPEs to be 'grandfathered' onto the register who would later be assessed, with all new applicants required to go through the portfolio and assessment process. With responsibilities and levels of competence defined, a UK Policy Statement was published in 2022 by the Institute of Physics and Engineering in Medicine (IPEM), jointly prepared with the British Nuclear Medicine Society, British Institute of Radiology and the Administration of Radioactive Substances Advisory Committee (ARSAC). This "IPEM Policy Statement" provides guidelines on appropriate levels of MPE support specific to nuclear medicine [7]. This followed similar international guidance from the European Federation of Medical Physics (EFOMP) [8] and the International Atomic Energy Agency (IAEA) [9]. The defined levels of support in the IPEM Policy Statement are given as ranges of whole-time equivalent (WTE) staff and are dependent on the variety and complexity of work performed in a department e.g. SPECT, PET, therapy, and the size of the department primarily defined by its number of scanners. Anecdotally within the community, there is a belief that nuclear medicine departments are struggling to reach the levels of MPE support listed in the guidelines. To address this, a group of heads of nuclear medicine physics departments in the UK were asked to participate in a survey to test the hypothesis that the nuclear medicine community were not able to meet the levels of MPE expressed in guidance. This paper presents the results of this survey and provides a commentary on the current and potential future course of MPE provision in the UK. Method Nuclear medicine departments in the UK were surveyed to determine their current and future expected levels of MPE support for their respective departments. Questions were asked about current levels of MPE and non-MPE medical physics staff, junior trainees supported (to understand future provision), and a self-assessment of how the department's MPE staffing compares to the levels in the IPEM Policy Statement [7]. The survey was sent via email to a database of nuclear medicine departments that are members of a 'Heads of Nuclear Medicine Physics' group established in March 2022. The survey was open between July 2022 and February 2023. The six questions posed are listed in Table 1. Table 1 - MPE survey questions 1. How many MPEs do you currently employ? (number of individuals and overall WTE)?2. How many Clinical Scientists who are not MPEs do you currently employ? (individuals and WTE)3. How many non-clinical scientist medical physics staff (e.g. technologists) do you currently employ (individuals and WTE)?4. How many Specialism STP (or equivalence) medical physics trainees are you currently supporting (individuals and WTE)?5. How many of your medical physicists are expected to submit their MPE portfolios of evidence within the next 6 months?6. What are the minimum and maximum levels of MPEs do you believe you need to cover all the services you support according to the ranges in the recent guidance? Please include your own site and any other sites to which you provide MPE support. MPE, medical physics expert; STP, scientific training program; WTE, whole-time equivalent. Results Of the 56 departments surveyed 40 responded, giving a response rate of 71%. Figure 1 shows the number of MPEs employed within surveyed departments. It was most common for departments to employ 1.0 WTE MPE with an average of 2.6 WTE (range 0.5–9.0 WTE).Fig. 1: Histogram showing the number of WTE MPEs employed by respondents.Most centres did not, according to their own self-assessment, meet the minimum number of MPE as stated in IPEM Policy Statement (Fig. 2). The average level of MPE support was 75% of the minimum levels specified in the IPEM Policy Statement, with a minimum of 20% and a maximum of 220%.Fig. 2: Histogram showing respondents' current MPE staffing WTE expressed as a percentage of the minimum guidance level for their service (based on self-assessment).There was no significant correlation found between the size of the department and the percentage of minimum guideline MPEs, although smaller centres were more likely to meet the recommendations (Fig. 3).Fig. 3: Correlation between the minimum level of MPE staffing according to departments' self-assessment and the actual MPEs employed as a percentage of the minimum guideline level.Eight sites (21% of respondents) had MPE numbers above the minimum recommendation (Fig. 4). It is important to note that the guidance only applies to MPEs and not Clinical Scientists, but if all HCPC-registered Clinical Scientists (not just MPEs) are included in the WTE employed, 26 sites (65%) would meet the minimum recommended WTE level, and if all medical physics staff in the department are included 31 sites (78%) of respondents meet this level.Fig. 4: Current WTE MPEs employed (crosses) and self-assessed ranges of WTE required according to guidance (grey bars) for all respondents, ordered by minimum guidance WTE.The survey showed that an additional 45 WTE MPE would be needed to meet the self-assessed minimum recommended levels stated by survey respondents. It was also found that there were 38 trainees with specialism in nuclear medicine or imaging with ionising radiation, and that 24 physicists were expected to submit their portfolio of evidence for recognition as a MPE within the next 6 months. Discussion The survey described in this paper provides a good snapshot of the current status of MPE provision in the UK, with 71% of surveyed sites responding. It is not known what percentage of all departments in the UK were captured in the survey, but the survey was widely distributed amongst the nuclear medicine physics community representing a range of different departments (including large regional centres supporting smaller departments) across all nations of the UK. We therefore believe that there is no inherent bias in the results presented. The survey showed that the majority (79%) of sites in the UK do not meet the minimum number of MPEs defined in IPEM Policy Statement. On average sites had 75% of the minimum recommended levels although there was a wide range of between 20% and 220%. These levels of MPE support were self-declared and were not validated or checked for consistency across sites, but this is nevertheless concerning. More positive was the fact that smaller sites seemed more likely to have an appropriate level of MPE support, although it is most likely that this will be a single individual employed at 1.0 WTE, implying there may be little resilience to cover sickness and annual leave. Many smaller sites will be supported by larger regional centres with potentially more depth of staffing for resilience. Our survey asked medical physics departments to include any smaller sites that they support in their calculation of overall MPE requirements. Therefore, the data do not separate out these smaller departments that do not employ their own medical physicists. However, this approach did ensure that the overall MPE requirements for regional services were captured. Based on supplied data it was calculated that a further 45 WTE MPE would be required to meet minimum recommendations. The number of current trainees specialising nuclear medicine was stated as 38, with 24 individuals aiming to submit their portfolio of evidence for MPE certification within the next 6 months. This will help to address the shortfall but does not account for attrition of the workforce through retirement or leaving the profession. These absolute numbers of forthcoming MPEs are not adjusted for the survey response, but we can forecast with reasonable certainty that there will be a deficit in the 'talent pool' of MPEs in the coming years, which will make it difficult to address the current shortfall. The process of collecting and submitting evidence for MPE portfolios takes some time, and given widespread staff shortages, this is often challenging to achieve within normal working hours. Furthermore, the process of assessment of submitted portfolios is time-consuming and performed centrally on a voluntary basis, with portfolios taking up to 6 months to assess. Streamlining the process of MPE certification should be considered, particularly given that there are individuals on the original grandfathered list who have yet to be formally assessed, and also that there is expected to be a method of re-registration based on Continuous Professional Development [10]. The IPEM Policy Statement on MPE staffing levels was compiled taking into account data on WTE MPE support levels from ARSAC Employer License applications [7]. However, quantification of WTE available MPE support is often open to interpretation. For example, a remote site might secure contracted MPE services from a larger centre and the MPE may attend the site 1 day each week, and are otherwise available for remote support. An applicant for an Employer License for such a site may enter either 0.2 or 1.0 WTE, depending on interpretation. Furthermore, the larger centre may also count the MPE that supports the remote site in their own allocation, effectively leading to double-counting and skewing of the apparent MPE coverage. The situation may be further complicated if MPEs also act as Radiation Protection Adviser, Radioactive Waste Adviser to one or multiple sites, as it is difficult to quantify the time allocated to each role. Recent revisions to the ARSAC Employer License application process have expanded the level of detail on remote- and on-site MPE support, but a risk of double-counting across centres still exists. Extrapolations based on historical ARSAC applications, without accounting for extant hub-and-spoke support structures, must therefore be treated with caution. Consideration should perhaps be given instead to adopting a more tailored, 'bottom up' approach, such as the methods proposed by EFOMP and the IAEA [8,9]. This may be more appropriate, particularly given that there is considerable variability in staffing mix, department structure, and the roles of physicists nationwide. The IPEM Policy Statement [7] is now being adopted by ARSAC as the standard when evaluating MPE support levels for new applications and renewals of Employer Licenses. The authors are aware of multiple sites that have been issued with short-term licenses contingent on a review and increase of MPE support provision. However, our survey indicates that the medical physics workforce does not currently exist to fulfil these demands. It should be welcomed that the role of the MPE and their areas of responsibility are better defined in our current legislation and that their highly valuable contribution to a safe and efficient clinical service is recognised in national guidance. However, there remains some lack of clarity around the extent to which MPEs could (or should) act in a senior supervisory role, potentially supported by a team of HCPC-registered Clinical Scientists and technologists. To draw an analogy, nuclear medicine departments are only required to entitle a single ARSAC Licensed Practitioner regardless of the size and complexity of their service. This Practitioner takes overall clinical responsibility for the medical exposures in the department, but other doctors may be entitled to carry out tasks as Operators, following protocols and guidance that have been approved by the ARSAC Licensed Practitioner. However, under current guidance, larger and more complex services are required to employ multiple MPEs, even if there is an establishment of Clinical Scientists and technologists to support their work. While both ARSAC Licensed Practitioners and MPEs hold significant responsibilities, it is clear that the responsibilities of the Practitioner is the greater of the two. One might argue that departments should also be compelled to employ more ARSAC Licensed Practitioners, but it is clear that there is currently an inconsistency in the required staffing levels across the two professional groups, yet there are significant recruitment challenges in both. Conclusion Our survey has shown there is currently significant nationwide challenges in meeting current guidance on MPE staffing levels in nuclear medicine departments. Although we identified many Clinical Scientists who are close to achieving MPE certification, these are not likely to be in sufficient numbers to address the current shortfall. Streamlining the application process for MPE certification should be a priority, to ensure that staff with adequate experience can be entitled as MPEs promptly by employers. Consideration should also be given to adopting more nuanced approaches to defining acceptable levels of scientific support for nuclear medicine services that takes account not only of service size and complexity, but also of the skill mix within the scientific workforce, and hub-and-spoke support models. This is particularly important if licensing decisions are to be made on the basis of these evaluations. Acknowledgements The authors wish to thank all the members of the Heads of Nuclear Medicine Physics group who contributed to this survey. Data presented previously at the British Nuclear Medicine Society Annual Meeting 2023 and published as abstract in Nuclear Medicine Communications 44(6):518–561, June 2023. Conflicts of interest There are no conflicts of interest.

Introduction The Internal Dosimetry Users Group has regularly surveyed UK molecular radiotherapy (MRT) activity in the UK for the past decade. Combined with data from a previous survey [1] we present results from 2007 and consecutive years from 2011 to 2021. Data were gathered in the same manner as previous surveys [2–4] from 39 UK centres (1 from Northern Ireland, 1 from Wales, 3 from Scotland, 34 from England, 3 privately run, 36 NHS centres), 7 more than in our most recent publication [4], collectively administering 64 614 treatments over the surveyed period. Previous publications of ours [2–4] have focussed on MRT for malignancies, here we will also present data from 2018 onwards on MRT use in benign conditions. Treatments identified were Na131I Radioiodine (RAI) for thyroid cancer, 131I-metaiodobenzylguanidine (131I-mIBG) and peptide receptor radionuclide therapy (PRRT) for neuroendocrine tumours (NETs), 89Sr-chloride, 153Sm-EDTMP and 223Ra-Chloride for bone metastases, MRT for haematological malignancies, selective internal radionuclide therapy (SIRT) for liver metastases, radio-labelled prostate specific membrane antigen (PSMA) therapies, RAI for benign thyroid conditions, radio-labelled colloid use for radiosynoviortheses and various agents used in small trials. Data from the last 4 years also include a breakdown, where available, between treatments given to adult or paediatric patients. Results and discussion From 2007 to 2021 we have seen an 87% increase in the number of cancer patients treated and a 231% increase in treatments given, as well as several sudden changes year on year in overall workload as shown in Fig. 1. Whilst established therapies with reliable sources of funding appear primarily subject to clinical demand, which may wax with increasing incidence, or wane as newer treatments take over, the workloads from newer therapies can be volatile and appear particularly sensitive to;Fig. 1: Total numbers of molecular radiotherapy patients treated (upper) and treatments given (lower) in each year of the survey for the 39 participating centres. mIBG, 131I-metaiodobenzylguanidine; PRRT, peptide receptor radionuclide therapy; PSMA, radio-labelled prostate specific membrane antigen therapy; RAI, radioiodine; SIRT, selective internal radionuclide therapy. changes to funding changes in clinical evidence regulatory approval, examples of which will be discussed below in relation to each form of MRT. When a change in these factors is anticipated for a treatment, we can perhaps use the data presented here to anticipate the subsequent changes in demand, and consequent pressures on workload, as will be discussed in the case of 177Lu-PSMA. Our data also show the impact on MRT of the COVID-19 pandemic on workload in 2020 and how different therapies recovered into 2021. Na131I radioiodine (RAI) for thyroid cancer Incidence of thyroid cancer has risen steadily over the past decade, increasing by 65% between 2006–2008 and 2016–2018 [5]. Our data on the use of Na131I Radioiodine (RAI) to treat thyroid cancer show a rise of 31% over the same period, but not following the same, steady trend as the incidence data, as seen in Fig. 2 and Table 1. Unlike other treatments discussed below, funding, evidence and regulatory approval are not limiting factors as the therapy is cheap and has been used successfully for decades. Provided that centres have adequate and sufficient facilities, the dominant driver on rates of treatment is likely rates of referrals, driven itself by factors specific to each individual site. Otherwise, the data show no obvious trend. Table 1 - Treatment statistics for centres administering radioiodine treatments for thyroid cancer Year Total treatments administered Centres administering Treatments per centre Mean/median SD/range 2007 1314 30 44/33 32/5–150 2011 1617 34 48/40 32/1–162 2012 1767 34 52/40 36/3–158 2013 1666 34 49/37 34/6–157 2014 1693 34 50/46 33/4–160 2015 1643 35 47/41 36/4–162 2016 1750 35 50/38 31/6–128 2017 1891 35 54/41 40/9–152 2018 1725 35 49/36 35/9–127 2019 1745 35 50/41 34/7–119 2020 1498 36 42/33 28/5–114 2021 1719 36 48/39 35/8–156 Fig. 2: Numbers of radioiodine treatments for thyroid carcinoma with the number of centres administering.The one exception is the impact of the COVID-19 pandemic. In March 2020 a statement issued on behalf of the National Cancer Research Institute (NCRI) Thyroid Cancer Subgroup on the use of RAI during the COVID-19 pandemic [6] supported halting RAI treatments for differential thyroid cancer patients at that time. Our data show a 14% drop from 2019 to 2020 and a near complete recovery in 2021 to 99% of the number of treatments given in 2019. Paediatric RAI treatments (data available from 2018–2021) were given in 9 centres averaging 2.9% of all RAI treatments for thyroid cancer across the survey group. Neuroendocrine cancer 131I-mIBG and PRRT were used to treat similar numbers of patients at the beginning of this surveyed period. Whilst NET incidence in the UK has increased [7], the use of 131I-mIBG has steadily declined, being given in fewer centres, in ever-decreasing numbers as seen in Fig. 3 and Table 2. 131I-mIBG was administered to paediatric patients (data available from 2018–2021) in three centres in total but predominantly in one, consisting of 22.6% of all 131I-mIBG treatments. The impact of the COVID-19 pandemic on 131I-mIBG treatments is hard to discern over the general downward trend given the low numbers involved. Table 2 - Treatment statistics for centres administering 131I-mIBG. 131I-mIBG, 131I-metaiodobenzylguanidine Year Total treatments administered Centres administering Treatments per centre Mean/median SD/range 2007 148 17 9/8 7/1–25 2011 120 19 6/5 5/1–21 2012 135 18 8/5 7/1–30 2013 103 18 6/5 4/1–15 2014 108 14 8/7 6/1–27 2015 87 15 6/5 4/1–14 2016 72 13 6/3 6/1–23 2017 79 15 5/4 5/1–18 2018 78 12 7/3 9/1–32 2019 54 12 5/4 3/1–10 2020 48 10 5/4 4/1–13 2021 64 12 5/5 4/1–16 Fig. 3: Total numbers of patients treated, treatments given and centres administering 131I-mIBG. 131I-mIBG, 131I-metaiodobenzylguanidine.PRRT treatment numbers by contrast have increased tenfold over the survey period with significant changes year on year within this time frame, as shown in Fig. 4 and Tables 3 and 4, consistent with the factors identified above. 177Lu-Dotatate, available commercially as Lutathera (Novartis, Basel, Switzerland) use rose steadily up to 2015 when it was cut from the Cancer Drugs Fund (CDF) in November of that year [8]. Numbers rose again and more sharply following positive results from the NETTER-1 trial (ClinicalTrials.gov ID NCT01578239) [9], EMA marketing authorisation in 2017 [10] and subsequent National Institute of Clinical Excellence (NICE) approval in August 2018 [11]. The use of 90Y-PRRT, having started as the dominant radiopharmaceutical, has declined over the survey period as centres previously administering it have switched to 177Lu-PRRT, and most new services have only used the 177Lu based agent. 2021 saw a halt in availability of cold kits for in house labelled 90Y-Dotatate [12], effectively halting its use for PRRT in the UK. Paediatric patients were treated with PRRT in only one centre, their treatments constituting 0.9% of all PRRT treatments given between 2018 and 2021. Table 3 - Treatment statistics for centres administering 90Y-PRRT Year Total treatments administered Centres administering Treatments per centre Mean/median SD/range 2007 124 3 41/42 36/5–77 2011 156 4 39/19 44/14–105 2012 104 6 17/15 17/1–44 2013 107 5 21/21 15/6–36 2014 109 6 18/17 12/2–38 2015 107 6 18/14 15/3–40 2016 94 5 19/15 14/5–40 2017 101 4 25/23 27/2–53 2018 84 2 42/42 14/32–52 2019 71 2 36/36 49/1–70 2020 35 2 18/18 23/1–34 2021 0 0 0/0 0/0–0 PRRT, peptide receptor radionuclide therapy. Table 4 - Treatment statistics for centres administering 177Lu-PRRT Year Total treatments administered Centres administering Treatments per centre Mean/median SD/range 2007 6 1 6/6 0/6–6 2011 149 7 21/21 19/1–53 2012 264 11 24/13 23/1–57 2013 433 12 36/27 40/2–144 2014 467 13 36/26 36/4–147 2015 614 17 36/24 50/2–215 2016 543 17 32/16 44/3–173 2017 376 15 25/7 39/1–133 2018 485 15 32/13 46/2–152 2019 1263 18 70/49 76/2–320 2020 1232 20 62/44 64/2–273 2021 1365 20 68/61 60/6–279 PRRT, peptide receptor radionuclide therapy. Fig. 4: Numbers of patients treated (pts), treatments (tx) given and centres administering peptide receptor radionuclide therapy using 90Y and 177Lu labelled radiopharmaceuticals.PRRT treatment numbers appear the least impacted by the COVID-19 pandemic within our survey as they fell only 5% in 2020 and grew again in 2021 reaching their highest level to date. Bone metastases MRT use for bone metastases has changed dramatically over the surveyed period. In 2007 this field consisted of mostly one-off administrations (one treatment per patient) of 89Sr-chloride and 153Sm-EDTMP treatments to palliate bone pain. These treatments have decreased steadily in usage over the surveyed period, eventually not being used at all in 2021, as shown in Fig. 5 and Tables 5 and 6. However, in 2013 223Ra-Chloride was shown through the ALSYMPCA trial (NCT00699751) [13] to not only control bone pain but also give a 2.8-month survival benefit to patients with castration-resistant metastatic prostate cancer (mCRPC) as compared to placebo. This was evident even at interim analysis after which the trial was cut short [13]. The patients treated in this trial are visible in our data from 2007 to 2011. The commercially available product Xofigo (Bayer, Leverkusen, Germany) was briefly included on the CDF between 2014 and 2015 [14] leading to a sharp increase in its use, before gaining NICE approval in 2016 [15]. This propelled its use so as to treat more than 6 times as many patients, with 22 times as many treatments, at its peak in 2017 as were ever treated in one year with the other bone seeking agents combined as seen in Fig. 6 and Table 7. Table 5 - Treatment statistics for centres administering 89Sr-chloride for bone metastases Year Total treatments administered Centres administering Treatments per centre Mean/median SD/range 2007 156 20 8/5 8/1–33 2011 119 18 7/4 7/1–26 2012 104 20 5/4 4/1–13 2013 29 11 3/2 2/1–7 2014 21 11 2/1 1/1–4 2015 15 7 2/1 2/1–6 2016 4 4 1/1 0/1–1 2017 3 2 2/2 1/1–2 2018 4 2 2/2 0/2–2 2019 0 0 0/0 0/0–0 2020 0 0 0/0 0/0–0 2021 0 0 0/0 0/0–0 Table 6 - Treatment statistics for centres administering 153Sm-EDTMP for bone metastases Year Total treatments administered Centres administering Treatments per centre Mean/median SD/range 2007 36 4 9/8 7/3–18 2011 36 6 6/5 6/1–18 2012 39 4 10/8 9/1–23 2013 40 7 6/4 5/1–15 2014 13 4 3/2 3/1–8 2015 11 4 3/2 2/1–6 2016 2 2 1/1 0/1–1 2017 6 1 6/6 0/6–6 2018 2 1 2/2 0/2–2 2019 4 2 2/2 0/2–2 2020 0 0 0/0 0/0–0 2021 0 0 0/0 0/0–0 Table 7 - Treatment statistics for centres administering 223Ra-Chloride for bone metastases Year Total treatments administered Centres administering Treatments per centre Mean/median SD/range 2007 32 2 16/16 10/9–23 2011 72 3 24/10 28/6–56 2012 23 3 8/6 5/4–13 2013 70 4 18/10 19/6–45 2014 943 16 59/52 57/1–222 2015 2713 21 129/150 87/2–276 2016 3627 24 151/172 79/22–302 2017 4305 24 179/173 106/2–366 2018 3576 26 138/142 79/11–291 2019 2621 27 97/94 51/10–193 2020 2558 28 91/85 57/1–241 2021 2715 30 91/73 60/2–246 Fig. 5: Numbers of patients treated (pts), treatments given (tx) and number of centres administering 89Sr and 153Sm radiopharmaceuticals for bone metastases.Fig. 6: Numbers of patients treated (pts), treatments given (tx) and number of centres administering 223Ra-Chloride for bone metastases.In 2017 the Medicines and Healthcare products regulatory Agency, and in 2018 the European Medicines Agency (EMA), issued recommendations against the use of 223Ra-Chloride alongside the combination of the hormone therapy abiraterone acetate (Zytiga, Janssen Biotech, Pennsylvania, USA) and the steroid prednisone/prednisolone. This followed interim analysis of the ERA 223 trial (NCT02043678) [16,17] which indicated an increased risk of bone fractures in patients receiving these treatments together. The full results of ERA 223 [18] further supported this conclusion and the use of 223Ra-Chloride dropped considerably up to 2019, but remained relatively steady in 2020 and 2021 despite the COVID-19 pandemic. PSMA for prostate cancer 177Lu-PSMA was first reported by responders to our survey in 2018 (Fig. 7 and Table 8), consisting of patients treated within the VISION trial (NCT03511664) which ceased recruitment in 2021. Results from the trial were published later that year [19] and showed a 4-month survival benefit for mCRPC patients treated with 177Lu-PSMA in addition to standard of care. By the end of 2021 the treatment was only available in the UK privately, via trials or through the early access to medicines scheme [20]. 177Lu-PSMA, under the brand name Pluvicto (Novartis, Basel, Switzerland), has been granted marketing authorisation by the EMA [21] and at the time of writing is being reviewed by NICE with the final conclusion expected in October 2023 [22]. While under NICE review the future for 177Lu-PSMA in the UK, in terms of demand and our capacity to meet it, remains uncertain. Table 8 - Treatment statistics for centres administering 177Lu-PSMA for prostate cancer Year Total treatments administered Centres administering Treatments per centre Mean/median SD/range 2018 1 1 1/1 0/1–1 2019 223 8 28/20 26/4–80 2020 239 8 30/2 47/1–131 2021 216 6 36/24 45/2–117 PSMA, prostate specific membrane antigen. Fig. 7: Number of patients treated (pts), treatments given (txs) and centres administering 177Lu and 227Th labelled PSMA for prostate cancer. PSMA, prostate specific membrane antigen.Experience with 223Ra-Chloride can serve to give us an indication, if not a precise prediction, of the demand that might be expected with 177Lu-PSMA. As discussed above, following NICE approval of 223Ra-Chloride, centres rapidly began giving many times more treatments than were given with pre-existing equivalent products. However, whilst patients treated with 223Ra-Chloride and 177Lu-PSMA have overlapping characteristics, as seen in the demographics of the ALSYMPCA and VISION trials [11,17], 177Lu-PSMA can be given to patients who have visceral as well as bone metastases. Furthermore, several trials are underway which could broaden the range of patients who might be shown to benefit from 177Lu-PSMA, such as PSMAfore (NCT04689828), PSMAddition (NCT04720157) and SPLASH (NCT04647526). As such the exact eligibility criteria determined by NICE for 177Lu-PSMA, if approved, will have a considerable impact on the size of the demand, which could well be greater than that experienced with 223Ra-Chloride. Based on our data it would seem unlikely that the UK has the capacity to meet such demand. In 2021 within the surveyed group 177Lu-PSMA was being given, in all but one case, in centres already treating with 177Lu-Dotatate. To meet a swell in demand for 177Lu-PSMA would create conflict for capacity in high volume PRRT centres such as these. Capacity both in terms of staffing and facilities but also limits in Environment Agency (EA) permits for radioactive waste accumulation and disposal. Whilst lower volume centres may be able to expand their workload within their EA limits, they would require considerable investment in facilities, staffing and training, including supporting diagnostics (a guide to which can be found in recent EANM guidance [23]). NHS commissioning decisions surrounding 177Lu-PSMA will therefore play a major role on the UK's ability to meet the demand for the treatment. In the case that capacity cannot meet demand, whether only initially or in the long term, this could lead to difficult decisions surrounding eligibility. 177Lu based agents have the benefit over primarily alpha emitters such as 223Ra-Chloride of convenient imaging and the potential to perform dosimetry. The importance of which has been recognised in legislation [24], guidelines from several UK legislative entities [25,26] as well as by many professional groups [27–30], particularly for this therapy. Provision of a dosimetry service will similarly require investment in facilities, equipment, staff and their training but would help stratify patients, if nothing else helping identify patients for whom the treatment and its associated cost will not be beneficial. 227Th labelled PSMA was given by one centre in this group as 227Th-BAY-2315497 within the clinical trial NCT03724747, also shown in Fig. 7. Haematological and other small volume treatments Haematological treatments remain, as identified in our previous publications [2–4], a small family of MRTs, often based around clinical trials for novel radiopharmaceuticals (Fig. 8). The largest, and possibly only 'routine', area is the use of 32P-phosphate to treat Polycythaemia Vera or Essential Thrombocythemia. Data for 32P-phosphate were sparse within our group, likely represent an under-estimate up to 2017, after which centres were specifically asked about 32P-phosphate and from the few given subsequently we can see that 95% given were for Polycythaemia Vera. Treatments for both conditions have declined sharply over recent years and stopped altogether from 2020 onwards.Fig. 8: MRT treatments given for haematological malignancies and other malignancies not included elsewhere.Included in Fig. 8 are the remaining treatments labelled as 'Other' in Fig. 1, those being small trial based treatments for Mesothelioma with BAY 2287411 (NCT03507452), HER2 receptor positive cancers with BAY 2701439 (NCT04147819) and locally advanced pancreatic cancer with 32P Oncosil (Oncosil Medical, New South Wales, Australia) (NCT03003078). Selective internal radionuclide therapy Selective internal radionuclide therapy (SIRT) use in the UK has been relatively unsteady over the surveyed period as seen in Fig. 9 and Tables 9 and 10. Initially being used to treat patients with metastases of colorectal cancer, it was available for a time through the CDF, from which it was cut in 2012, followed by a period of Commissioning through Evaluation (CtE) where it was available in limited numbers in a select number of centres from 2013 to 2017 [31]. Results of trials of both 90Y SIR-Spheres (SIRTeX, Sydney, New South Wales, Australia) [32], and later 90Y-Theraspheres (Nordion, Ottawa, Ontario, Canada) [33] and the CtE commissioning report [31] did not show a survival benefit with these treatments for the patient cohort. SIRT, not including 166Ho-QuiremSpheres (Terumo, Tokyo, Japan), has now had NICE approval for a more limited set of patients with hepatocellular carcinoma [34]. Treatment numbers dropped substantially after 2016, remaining relatively steady from 2018 onwards including during the COVID-19 pandemic. Table 9 - Treatment statistics for centres administering SIRT treatments using SIRTeX SIR-Spheres Year Total treatments administered Centres administering Treatments per centre Mean/median SD/range 2007 23 2 12/12 9/5–18 2011 85 9 9/6 9/1–27 2012 178 14 13/9 11/1–36 2013 158 14 11/9 10/1–31 2014 231 14 17/15 13/3–45 2015 222 15 15/13 12/2–45 2016 275 14 20/17 10/7–38 2017 179 14 13/11 10/1–32 2018 112 13 9/5 8/1–23 2019 93 11 8/6 7/1–19 2020 77 9 9/6 8/1–22 2021 89 9 10/10 6/2–19 SIRT, selective internal radionuclide therapy. Table 10 - Treatment statistics for centres administering SIRT treatments using BTG TheraSphere Year Total treatments administered Centres administering Treatments per centre Mean/median SD/range 2007 1 1 1/1 0/1–1 2011 9 2 5/5 2/3–6 2012 10 2 5/5 0/5–5 2013 22 8 3/3 2/1–5 2014 56 12 5/4 4/1–16 2015 121 15 8/7 8/1–28 2016 97 13 7/4 8/1–29 2017 41 10 4/3 4/1–15 2018 64 6 11/9 10/1–28 2019 60 9 7/4 6/1–21 2020 52 6 9/7 8/1–22 2021 0 0 0/0 0/0–0 SIRT, selective internal radionuclide therapy. Fig. 9: Total number of treatments given and centres administering selective internal radionuclide therapy using SIRTeX SIR-spheres, BTG TheraSpheres and Terumo QuiremSpheres.MRT for benign conditions Benign conditions have only been formally included in our survey from 2018 onwards and do not form part of the data included in Fig. 1, but are shown in Fig. 10 and Table 11. Thyrotoxicosis is relatively common in the UK [35] and within our survey group lead to over 2300 Na131I treatments in 2018 and 2019, making up the vast majority of MRT uses for benign conditions. The COVID-19 pandemic appears to have had a much larger impact on this treatment than any other covered in this survey. Whilst delays in treatment during the height of the pandemic were supported by the relevant UK professional bodies [36] as with the use of radioiodine for thyroid cancer, treatment rates fell by 51% in 2020 and only partially recovered in 2021. This as compared to a drop of only 15% in RAI for malignancies in 2020 followed by a near-complete recovery in 2021 to pre-pandemic levels. Whilst the larger reduction in treatment numbers in 2020 for this benign condition is perhaps understandable as compared to treatments for malignancies, the poor recovery in 2021 points perhaps to an ongoing effect of COVID-19 on the benign thyroid treatment pathway. Table 11 - Treatment statistics for centres treating benign conditions Treatment Year Total treatments administered Centres administering Treatments per centre Mean/Median SD/Range RAI benign thyroid 2018 2326 36 65/51 53/7–269 2019 2368 36 66/54 52/12–295 2020 1169 34 34/28 26/4–98 2021 1582 34 47/33 38/2–191 90Y synoviortheses 2018 37 7 5/2 5/1–12 2019 41 7 6/3 7/1–19 2020 23 7 3/1 5/1–15 2021 27 8 3/3 2/1–7 186Re synoviortheses 2018 16 3 5/1 8/1–14 2019 11 2 6/6 6/1–10 2020 10 2 5/5 4/2–8 2021 17 3 6/5 5/1–11 RAI, radioiodine. Fig. 10: Number of treatments given and centres administering radiopharmaceuticals for benign conditions.Radiosynoviortheses are performed in small numbers in a similarly small number of centres and, whilst data are limited, appear to have also reduced in numbers due to the COVID-19 pandemic. Conclusion In a cohort of 39 UK centres, MRT was used to treat 87% more cancer patients in 2021 than in 2007, with 231% more treatments. Usage of new therapies appears heavily influenced by funding, clinical evidence and regulatory approval. In this survey, the effects of these were seen most clearly for 177Lu-PRRT, 223Ra-Chloride and SIRT. 177Lu-PRRT and SIRT grew in popularity over several years despite constraints in funding as key trials were ongoing. On publication of these trials and subsequent regulatory decisions their usage diverged with 177Lu-PRRT growing by 160% from 2018 to 2019 and remaining high thereafter, whilst SIRT declined to nearly a third of its 2016 peak by 2021. 223Ra-Chloride usage prior to regulatory approval was minimal, likely limited to trial patients only, with a meteoric increase thereafter over a period of little over three years, followed by a similarly sudden fall as with SIRT from 2017 to 2019 to around 60% of its peak popularity, remaining steady thereafter. The impact of the COVID-19 pandemic is visible as a reduction in workload in 2020 for some, although not all, treatment types, with most areas partly or fully recovering in 2021. The greatest effect was seen in the use of radioiodine for treatment of thyrotoxicosis where treatment numbers reduced by around half and fell far short of a full recovery in 2021. This survey provides numerical evidence of changes which many will have experienced locally or anecdotally, that of considerable and sometimes sudden growth in therapy workload. We hope that this data help support calls for investment in resources and staffing, especially given the recently identified NHS staffing shortages [37], in MRT as well as accompanying diagnostics. This will be crucial to keep pace with this growth and demand, in particular for treatments with a large referral base, as we have seen with 223Ra-Chloride and may see to a greater degree with 177Lu-PSMA. The scale of growth alongside finite resources presents a need for optimisation of how these treatments are given, and a golden opportunity to exploit the untapped potential of patient-specific dosimetry.

Positron emission tomography (PET) is a widely used imaging modality for the diagnosis and treatment of oncologic diseases. In this study, we evaluated the performance of digital PET/CT systems using subcentimeter microsphere inserts in a NEMA IEC Body Phantom. The digital system was compared with a non-digital PET scanner using the same image reconstruction method. Results revealed that the digital system maintained higher detectability for smaller spheres with an average of 1 Likert score higher for lesions under 7.9mm, indicating its ability to detect smaller lesions more effectively than the non-digital system. Furthermore, we observed that the drop-off in contrast recovery occurs at smaller microspheres in the digital PET system compared with that for a non-digital PET scanner. This suggests that digital PET may require the use of smaller spheres in image quality testing to ensure accurate comparison of performance between digital systems. This implies that digital systems can more accurately and effectively distinguish subtle differences in image intensity and spatial distributions of intensity, leading to improved lesion visibility and detection, which is likely due to the superior imaging characteristics offered by underlying detection technology.

Nuclear medicine imaging modalities like computed tomography (CT), single photon emission CT (SPECT) and positron emission tomography (PET) are employed in the field of theranostics to estimate and plan the dose delivered to tumors and the surrounding tissues and to monitor the effect of the therapy. However, therapeutic radionuclides often provide poor images, which translate to inaccurate treatment planning and inadequate monitoring images. Multimodality information can be exploited in the reconstruction to enhance image quality. Triple modality PET/SPECT/CT scanners are particularly useful in this context due to the easier registration process between images. In this study, we propose to include PET, SPECT and CT information in the reconstruction of PET data. The method is applied to Yttrium-90 ( ^90 Y) data. Data from a NEMA phantom filled with ^90 Y were used for validation. PET, SPECT and CT data from 10 patients treated with Selective Internal Radiation Therapy (SIRT) were used. Different combinations of prior images using the Hybrid kernelized expectation maximization were investigated in terms of VOI activity and noise suppression. Our results show that triple modality PET reconstruction provides significantly higher uptake when compared to the method used as standard in the hospital and OSEM. In particular, using CT-guided SPECT images, as guiding information in the PET reconstruction significantly increases uptake quantification on tumoral lesions. This work proposes the first triple modality reconstruction method and demonstrates up to 69 ^90 Y patient data. Promising results are expected for other radionuclide combination used in theranostic applications using PET and SPECT.

Abstract Introduction Commissioning, calibration, and quality control procedures for nuclear medicine imaging systems are typically performed using hollow containers filled with radionuclide solutions. This leads to multiple sources of uncertainty, many of which can be overcome by using traceable, sealed, long-lived surrogate sources containing a radionuclide of comparable energies and emission probabilities. This study presents the results of a quantitative SPECT/CT imaging comparison exercise performed within the MRTDosimetry consortium to assess the feasibility of using 133Ba as a surrogate for 131I imaging. Materials and methods Two sets of four traceable 133Ba sources were produced at two National Metrology Institutes and encapsulated in 3D-printed cylinders (volume range 1.68–107.4 mL). Corresponding hollow cylinders to be filled with liquid 131I and a mounting baseplate for repeatable positioning within a Jaszczak phantom were also produced. A quantitative SPECT/CT imaging comparison exercise was conducted between seven members of the consortium (eight SPECT/CT systems from two major vendors) based on a standardised protocol. Each site had to perform three measurements with the two sets of 133Ba sources and liquid 131I. Results As anticipated, the 131I pseudo-image calibration factors (cps/MBq) were higher than those for 133Ba for all reconstructions and systems. A site-specific cross-calibration reduced the performance differences between both radionuclides with respect to a cross-calibration based on the ratio of emission probabilities from a median of 12–1.5%. The site-specific cross-calibration method also showed agreement between 133Ba and 131I for all cylinder volumes, which highlights the potential use of 133Ba sources to calculate recovery coefficients for partial volume correction. Conclusion This comparison exercise demonstrated that traceable solid 133Ba sources can be used as surrogate for liquid 131I imaging. The use of solid surrogate sources could solve the radiation protection problem inherent in the preparation of phantoms with 131I liquid activity solutions as well as reduce the measurement uncertainties in the activity. This is particularly relevant for stability measurements, which have to be carried out at regular intervals.

Monte Carlo (MC) simulations are used in nuclear medicine imaging as they provide unparalleled insight into processes that are not directly experimentally measurable, such as scatter and attenuation in an acquisition. Whilst MC is often used to provide a ‘ground-truth’, this is only the case if the simulation is fully validated against experimental data. This work presents a quantitative validation for a MC simulation of a single-photon emission computed tomography (SPECT) system. An MC simulation model of the Mediso AnyScan SCP SPECT system installed at the UK National Physical Laboratory was developed in the GATE (Geant4 Application for Tomographic Emission) toolkit. Components of the detector head and two collimator configurations were modelled according to technical specifications and physical measurements. Experimental detection efficiency measurements were collected for a range of energies, permitting an energy-dependent intrinsic camera efficiency correction function to be determined and applied to the simulation on an event-by-event basis. Experimental data were collected in a range of geometries with ^99m Tc for comparison to simulation. The procedure was then repeated with ^177 Lu to determine how the validation extended to another isotope and set of collimators. The simulation’s spatial resolution, sensitivity, energy spectra and the projection images were compared with experimental measurements. The simulation and experimental uncertainties were determined and propagated to all calculations, permitting the quantitative agreement between simulated and experimental SPECT acquisitions to be determined. Statistical agreement was seen in sinograms and projection images of both ^99m Tc and ^177 Lu data. Average simulated and experimental sensitivity ratios of ( 0.991 ± 0.011 ) were seen for emission and scatter windows of ^99m Tc, and ( 0.897 ± 0.014 ) and ( 0.839 ± 0.014 ) for the 113 and 208 keV emissions of ^177 Lu, respectively. MC simulations will always be an approximation of a physical system and the level of agreement should be assessed. A validation method is presented to quantify the level of agreement between a simulation model and a physical SPECT system.

Positron Emission Tomography and Computed Tomography (PET-CT) is a vital imaging technique for accurate cancer diagnosis, staging, and treatment planning, offering complementary morphological and anatomical information. A 5-layer 3D convolutional deep learning texture model was employed to identify glycolytic regions in PET-CT data, achieving an average sensitivity and specificity of 96.1% and 99.4%, respectively, for binary classification targeting primary tumor patches. Using a dataset of PET-CT data from 486 esophageal patients, we analyzed network activations across each layer for characteristic activation patterns of four glycolytic uptake classes: primary tumor, bladder, liver, and myocardium. PCA analysis of the activations was performed to isolate uncorrelated features learned during training and reveal unique feature clusters in PCA space, demonstrating that glycolytic regions with high SUV values exhibit distinct textures learnable by deep learning architectures. This information was used to prune low activation probability nodes in the network, resulting in a more efficient deployable network with slightly improved classification performance. A comprehensive quantitative evaluation of redundant filters in the network, examining filter combinations that result in positive (tumor-present) and negative (tumor-absent) predictions across multiple patients will be presented, alongside preliminary results on the use of AI for automatic staging.

BACKGROUND:Selective internal radiation therapy with Yttrium-90 microspheres is an effective therapy for liver cancer and liver metastases. Yttrium-90 is mainly a high-energy beta particle emitter. These beta particles emit Bremsstrahlung radiation during their interaction with tissue making post-therapy imaging of the radioactivity distribution feasible. Nevertheless, image quality and quantification is difficult due to the continuous energy spectrum which makes resolution modelling, attenuation and scatter estimation challenging and therefore the dosimetry quantification is inaccurate. As a consequence a reconstruction algorithm able to improve resolution could be beneficial.METHODS:In this study, the hybrid kernelised expectation maximisation (HKEM) is used to improve resolution and contrast and reduce noise, in addition a modified HKEM called frozen HKEM (FHKEM) is investigated to further reduce noise. The iterative part of the FHKEM kernel was frozen at the 72nd sub-iteration. When using ordered subsets algorithms the data is divided in smaller subsets and the smallest algorithm iterative step is called sub-iteration. A NEMA phantom with spherical inserts was used for the optimisation and validation of the algorithm, and data from 5 patients treated with Selective internal radiation therapy were used as proof of clinical relevance of the method.RESULTS:The results suggest a maximum improvement of 56% for region of interest mean recovery coefficient at fixed coefficient of variation and better identification of the hot volumes in the NEMA phantom. Similar improvements were achieved with patient data, showing 47% mean value improvement over the gold standard used in hospitals.CONCLUSIONS:Such quantitative improvements could facilitate improved dosimetry calculations with SPECT when treating patients with Selective internal radiation therapy, as well as provide a more visible position of the cancerous lesions in the liver.

Objectives As part of the 75-Selenium homocholic acid taurine (SeHCAT) study, counts are acquired as a baseline to allow the calculation of the retention at 7 days. In this work, we evaluated whether it was possible to replace the baseline image with a predictive model based on the patient's height and weight. Method Height and weight data from 723 patients scanned at three hospitals using seven gamma cameras were compiled. A number of different models were trialled, with fitting parameters determined by regression. A predictive model based on height and logarithm of weight was found to have the best correlation with the measured counts in the 3-h study. Results There was a strong correlation (R-2 = 0.91) between the measured counts and the predicted counts using a model based on height and logarithm of weight. Treating the standard SeHCAT test result as the gold standard, the test result when predicted baseline counts were used had a sensitivity and specificity of 97.5 and 98.0%, respectively, at a threshold of 15%. In total 694/723 (96.0%) of patients had no change to their severity grading when using the predicted baseline counts. Conclusion This work presents a model that was able to predict the counts in the 3 h SeHCAT study for patients on seven gamma cameras. This can enable a single scan study, giving significant savings to patient and staff time and imaging resources.

The recent implementation of the first clinical triple modality scanner in STIR enables investigation of the possibility of triple modality image reconstruction. Such a tool represents an important step toward the improvement of dosimetry for theranostics, where the exploitation of multi-modality imaging can have an impact on treatment planning and follow-up. To give a demonstration of triple modality image reconstruction we used data from a NEMA phantom that was filled with Yttrium-90 ( 90 Y), which emits Bremsstrahlung photons detectable with SPECT as well as gamma rays that can go through pair production, therefore creating positrons that make PET acquisition possible. The data were acquired with the Mediso AnyScan SPECT/PET/CT. Different ways of including multiple side information using the kernelised expectation maximisation (KEM) and the Hybrid KEM (HKEM) were used and investigated in terms of ROI activity and noise suppression. This work presents an example of application with 90 Y but it can be extended to any other radionuclide combination used in Theranostic applications.

Background: Selective internal radiation therapy with Yttrium-90 microspheres is an effective therapy for liver cancer and liver metastases. Yttrium-90 is mainly a high-energy beta particle emitter. These beta particles emit Bremsstrahlung radiation during their interaction with tissue making post-therapy imaging of the radioactivity distribution feasible. Nevertheless, image quality and quantification is difficult due to the continuous energy spectrum which makes resolution modelling, and attenuation and scatter estimation challenging. Methods: In this study, a modified hybrid kernelised expectation maximisation is used to improve resolution and contrast and reduce noise. The iterative part of the kernel was frozen at the 72nd sub-iteration to avoid over-fitting of noise and background. A NEMA phantom with spherical inserts was used for the optimisation and validation of the algorithm, and data from 5 patients treated with Selective internal radiation therapy were used as proof of clinical relevance of the method. Results: The results suggest a maximum improvement of 56% for region of interest mean recovery coefficient at fixed coefficient of variation and better identification of the hot volumes in the NEMA phantom. Similar improvements were achieved with patient data, showing 47% mean value improvement over the gold standard used in hospitals. Conclusions: Such quantitative improvements could facilitate improved dosimetry calculations with SPECT when treating patients with Selective internal radiation therapy, as well as provide a more visible position of the cancerous lesions in the liver.

The SEL-I-METRY trial (EudraCT No 2015-002269-47) is the first multicentre trial to investigate the role of I-123 and I-131 SPECT/CT-based tumour dosimetry to predict response to radioiodine therapy. Standardised dosimetry methodology is essential to provide a robust evidence-base for absorbed dose-response thresholds for molecular radiotherapy (MRT). In this paper a practical standardised protocol is used to establish the first network of centres with consistent methods of radioiodine activity quantification. Nine SPECT/CT systems at eight centres were set-up for quantitative radioiodine imaging. The dead-time of the systems was characterised for up to 2.8 GBq I-131. Volume dependent calibration factors were measured on centrally reconstructed images of I-123 and I-131 in six (0.8-196 ml) cylinders. Validation of image quantification using these calibration factors was performed on three systems, by imaging a 3D-printed phantom mimicking a patient's activity distribution. The percentage differences between the activities measured in the SPECT/CT image and those measured by the radionuclide calibrator were calculated. Additionally uncertainties on the SPECT/CT-based activities were calculated to indicate the limit on the quantitative accuracy of this method. For systems set-up to image high I-131 count rates, the count rate versus activity did not peak below 2.8 GBq and fit a non-paralysable model. The dead-times and volume-dependent calibration factors were comparable between systems of the same model and crystal thickness. Therefore a global calibration curve could be fitted to each. The errors on the validation phantom activities' were comparable to the measurement uncertainties derived from uncertainty analysis, at 10% and 16% on average for I-123 and I-131 respectively in a 5 cm sphere. In conclusion, the dead-time and calibration factors varied between centres, with different models of system. However, global calibration factors may be applied to the same system model with the same crystal thickness, to simplify set-up of future multi-centre MRT studies.

PET-CT scans using 18 F-FDG with a co-registered CT scan are increasingly used to detect cancer. This paper compares deep learning-based lesion detection tools trained on PET, CT and combined modality data. 486 pre-contoured scans were used from a retrospective cohort study into esophageal cancer. Scans were partitioned into training, validation and test sets with an 80:10:10 ratio. 1000 image segments were generated from each scan, with tumor present segments located on the contoured lesion and tumor absent segments distributed randomly within the patient but excluding the tumor. PET and CT image segments were used to train a separate dedicated 5-layer convolutional neural networks (CNN). Testing on segments from unseen scans resulted in an accuracy of greater than 95% for the PET data, and greater than 90% for CT data.