PURPOSE:Assess consistency of end-to-end dosimetry audits used by six Global Quality Assurance of Radiation Therapy Clinical Trials Harmonization Group (GHG) member organizations to harmonise audits and reduce audit overlap in multinational trials while maintaining quality. METHODS:Prior work developed and validated 16 head and neck reference plans, based on established international dosimetry audits for intensity modulated radiotherapy treatments. Realistic modifications, developed from reported variations in clinical practice, were introduced into nine copies of each plan, generating 144 modified plans. These plans were grouped as acceptable (should pass) and unacceptable (should fail) using plan assessment metrics and action limits on CTVmean, CTVD95, and OARD0.03cc. In the current work, each GHG audit system measured the error-free reference plans on its own phantom using its standard workflow. The measured error-free plans were then compared to the dose calculations of the modified plans. Outcomes were expressed as pass/fail, which were then compared to the "should pass/should fail" benchmark to determine the sensitivity and specificity of each system. An optimal action limit was determined for each audit system to achieve a common sensitivity across all audit systems. RESULTS:All audit systems reliably identified failing plans (sensitivity 0.92-1.0; specificity 0.40-0.91) with 5% ΔCTVmean assessment action thresholds. Adjusting the action limit revealed that each audit system was tuned to detect different error thresholds (3.3% - 5.7%). Changing audit system action limits specificity, while preserving system sensitivity. CONCLUSION:The comparably high sensitivity across all audit systems could allow harmonising of dosimetry audits for clinical trials on an international scale based on sensitivity alone. Future work harmonising specificity would help streamline credentialing for international clinical trials.

Radiotherapy methods have improved with time through technological developments, although with increasing complexity. However, radiotherapy quality can vary significantly across clinics. Quality assurance (QA) systems have developed with treatment methods to maintain and improve safety, accuracy and consistency for routine clinical practice and for clinical trials.Patient-specific quality assurance (PSQA) is an essential component of QA for safe and effective radiotherapy, ensuring that the correct dose is delivered to the correct location for each individual patient. PSQA for external beam MV photon treatment is reviewed, specifically considering dosimetric verification of treatment plan delivery and examining its evolution as modern radiotherapy methods have developed.The principal radiotherapy failure modes are summarized, from a risk-based perspective.Current standard PSQA approaches rely primarily on pretreatment detector-based measurements and have limitations in identifying some failure modes, e.g. ignoring inter- and intra-fraction patient variability, or in handling evolving methods such as online adaptive radiotherapy. Other PSQA approaches and workflows have emerged to address the limitations and challenges, including secondary dose calculations, log file based PSQA, and combining complementary methods.Next-generation PSQA is evolving to improve resource-effectiveness via data-driven and risk-based methodologies. Increasingly, PSQA will combine fast dose recalculation and daily log file/image-based 3D dose reconstruction with online/real-time EPID-based in vivo verification measurements. Respectively, these can enable clinically meaningful structure-based evaluation and continuous treatment monitoring with delivery modification where necessary. Automation and AI-driven analytics will support efficiency and scalability. PSQA must keep on adapting as radiotherapy techniques develop, to continue to ensure their quality and consistency.

BACKGROUND:There is large variability in patient specific quality assurance (PSQA) devices, techniques and protocols used clinically in radiotherapy. The SEAFARER methodology enables centres to evaluate their PSQA system's ability to detect intentionally introduced errors and compare their findings with community results. AIM:This study assessed the performance of PSQA systems in detecting simulated delivery errors for a head and neck radiotherapy case. METHODS:A commercial dose-mimicking algorithm was employed to create plans of similar quality and robustness for common linac models based on an established plan. Using Python scripting, eleven copies of these plans were created and modified to simulate different delivery errors which were classified based on their dosimetric impact as 'should-pass' or 'should-fail'. Participating centres were asked to use their clinical PSQA methodologies to determine which of the modified plans passed their PSQA processes when compared to the unmodified plan's dose prediction. RESULTS:Eighty-nine submissions were received from 44 centres. Using their clinical PSQA systems, 48% (21/44) of centres passed at least one 'should-fail' plan. Overall sensitivity and specificity across all devices were 79% and 82%, respectively. Multiple centres reported a review or change of their PSQA protocol. Five common PSQA devices (used for 5+ submissions) were included in a comparison. Sensitivities ranged 0-100%, with every common device having at least one perfect score of 100% sensitivity and 100% specificity. CONCLUSION:Sensitivity and specificity of PSQA systems varied greatly between centres. User choices rather than inherent characteristics determine the performance of common PSQA devices.

Background and purpose:Spinal Stereotactic Body Radiotherapy (SBRT) is among the most complex treatments currently delivered. A multi-centre dosimetry audit evaluated the accuracy of spinal SBRT treatment delivery and the impact of different dose reporting modes (DRM). Methods and materials:The audit used anthropomorphic phantoms containing alanine in the Planning Target Volume (PTV) and Gafchromic™ EBT3 film in the axial plane, with a combination of onsite and remote audits due to Covid travel restrictions. Centres used their local planning protocol and technique to create a clinically acceptable treatment plan, following national guidance. Results:Fifty-nine plans from 44 treatment planning systems at 41 centres were analysed. The mean PTV dose difference was 1.2% [-6.5-8.5%] with alanine and 1.0% [-7.0-8.5%] within the 100% isodose for film. Alanine measurements were, on average, higher than the calculated dose for all plans, but lower for the Dw,m specifically. For alanine and film, the choice of DRM was statistically significant.The mean distance to agreement and average Centre of Dose difference for films was 0.82 mm [0.35-1.7 mm] and 0.78 mm [0.1-1.7 mm] respectively. The choice of DRM was not significant for either metric. Conclusions:This audit demonstrated that the majority of centres are delivering spinal SBRT consistently, with acceptable dosimetric and geometric accuracy. However, it also highlighted the challenges of verifying doses reported in Dm,m and Dw,m, as there was a statistically significant difference with the measured dose when stratified by DRM.

Standardised digital records can improve access and quality of health services and enable meta-analysis of data which may reveal unknown patterns, which improve our understanding of the data. In this study, we report on meta-analysis of data curated from advanced radiotherapy dosimetry audits conducted at hospitals across the UK using test objects developed at the National Physical Laboratory. This meta-analysis highlights hospitals which are performing within expectation, or outside of expected intervals and would benefit from measurement support. Anonymised hospitals with low precision or accuracy treatment plans are identified, enabling support and improvements where appropriate. The results presented may be used to provide insight to hospitals and inform areas of focus for improved predictions of radiation dose that are tailored to a given hospital. Moreover, this analysis can enable auditors and regulators to provide additional services or recommendations, and potentially identify previously unknown patterns or dependencies in the data.

Background and purpose:The role of dosimetry audits is well established in the development and verification of radiotherapy safety. Differences in planning and beam modelling make inter-centre comparisons challenging, which can be addressed through distribution of centrally created plans. This study developed a centralised planning approach applicable to multiple audit methodologies, using an example of remote patient specific quality assurance assessment, increasing the interpretability of results and facilitating automation and scalability. Material and methods:Starting with an established plan which met all clinical goals, a commercial dose mimicking algorithm was used to replicate this plan to be suitable for multiple treatment machines. Beam and machine limitation data were collected from participating centres to develop universally acceptable beam models. The influence of variation in beam modelling parameters among centres was assessed by creating additional models using the 2.5th, 25th, 75th and 97.5th percentiles of previously reported data. Multi-leaf collimator angle and leaf position, gantry angle and output deviations were then introduced into copies of these plans. Results:Introduced delivery errors caused consistent change in dose metrics across machine models (excluding outliers) with a median (range) standard deviation of 1.0 % (from 0.1 % to 1.7 %) demonstrating similar robustness. Beam model variation did not change whether simulated delivery errors were clinically impactful or not for 95 % of tested plans. Conclusion:This study lays the foundation for future standardised methodology for dosimetry audits by providing a centralised planning approach that allows a more consistent assessment of centres.

In the current digital age, data from measurements are collected routinely for a wide range of applications. Curating these data in structured tables can greatly enhance data access, searchability and reuse through data queries. In addition, the use of digital forms to input data can lower the incidence of human error. As use of digital technologies increases, storing digital information in standardised and searchable formats is crucial for complex areas such as healthcare, and in particular in those areas related to clinical decision making, such as in radiotherapy. Standardised digital records can improve access and quality of health services and enable meta-analysis of data which may reveal previously unknown patterns, clusters or correlations improving our understanding of the data, measurements, and their application domains. We use retrospective data curated from a range of advanced Stereotactic Body Radiotherapy (SBRT) dosimetry audits targeted at the lungs, conducted at hospitals across the UK to obtain insights into audit performance. We compare the dose predicted by each hospital’s treatment planning system (TPS) and the measured dose in dosimeters placed in a test object. Data is categorised by the TPS used, allowing a comparison of audited TPS to examine comparability between systems and hospitals. We observe that different TPS are comparable, showing similar variability across all systems. Being able to compare like-for-like systems is critical to understanding the source of any deviations and ultimately improve measurements and patient care. Comparing all audits allows hospitals and auditors to highlight instances where audits have highly repeatable measurements, i.e., low variance; have highly variable measurements; have small differences between measured and predicted values; or are outside the 95 % confidence interval for dose difference. These results may be used to provide insight to hospitals by giving a quantitative comparison between them and other sites using similar equipment. This information may inform areas of focus for improved predictions of dose, or measurements, that are tailored to a given hospital, such as focusing on accuracy or precision, or both. Moreover, this can enable auditors and regulators to provide additional services or recommendations, inform or motivate new standards, set suitable tolerances for future audits, and potentially identify previously unknown patterns or dependencies in the data. Statistical analysis of intra-audit measurements reveals outliers and underlying distributions in the data, which may be useful when analysing audit performance. For example, audit measurements outside the 95 % confidence interval may be easily flagged by an auditor and a follow-up audit scheduled. Where hospitals’ measurements can be improved, auditors can assist with training in good measurement technique, as well as help develop new and improved protocols. We also identify a large proportion of missing data related to the TPS and the requirement for standardised data collection in order to perform comparisons. Future work will continue to analyse the audit data as the database grows, allowing further meta-analysis of standardised data. In addition, we will investigate and compare other audit types, such as spine SBRT, to identify new trends and patterns within these audits.

PURPOSE:To develop a practical framework for creating a diverse set of validated reference plans (varying in complexity) and implement a workflow to introduce beam modeling, calibration, and delivery errors into the reference cohort to test and compare various dosimetry audit methodologies. METHODS:Sixteen IMRT and VMAT reference plans were created, using RayStation software, for four phantom geometries based on established credentialing cases from participating Global Harmonization Group (GHG) members. These reference plans were first validated in a multi-ion-chamber phantom. Nine dosimetric errors (perturbations) were introduced into the plans by modifying beam model and/or delivery parameters (MLC-offset, MLC-transmission, leaf-tip-width, PDD, beam calibration, and MLC-position) based on documented community distributions of errors; this produced 144 plans. The dose impact on the clinical target volume (CTV) and organs at risk (OARs) was determined, and a range of classifications was developed to determine if the perturbed plan should pass or should fail an audit. RESULTS:Introducing errors into the reference plans impacted each plan differently. Dose perturbations ranged from <1% to >10% in the mean dose to the CTV and <10% to >30% in the near maximum dose to OAR (D0.03). The 144 plans included clear "acceptable" and "unacceptable" scenarios, with significant changes in dose (relative to baseline reference values), as well as near pass/fail threshold results. Plan complexity was found to have a strong impact on dose deviation, and the mean MLC Gap metric was found to best capture this relationship. CONCLUSION:This study presented a framework to develop a set of reference plans and perturbations that can be used to assess and compare various audit and PSQA methodologies. The GHG has developed this framework as part of our ongoing work to test the comparability of their audit systems; this framework supports our work of aligning international dosimetry audits across the globe.

INTRODUCTION:Microdosimetry provides a statistical, measurable description of energy deposition at the sub-cellular level, directly linked to biological effectiveness. In recent years its application to proton therapy has shown promising improvements in the accuracy of radiobiological modelling. This paper introduces a novel approach for integrating microdosimetric quantities into the treatment planning process. MATERIAL AND METHODS:This study aims to demonstrate the feasibility of a method for incorporating microdosimetric quantities into TPS, through the creation of look-up tables (LUT) that account for the stochastic nature of energy deposition occurring during a proton treatment irradiation. RESULTS:This work provides a preliminary set of LUT that relate the kinetic energy of incoming protons to the first-order stochastic means obtained from the corresponding microdosimetric spectra to proton kinetic energy. Such LUT are pre-produced via Monte Carlo simulations with sub-micrometre precision and can be immediately implemented into commercial TPSs. The resulting quantities are validated against complete Monte Carlo simulations, showing an agreement within 1 keV/µm for y¯F, y∗, and y¯D from the entrance region through the 20 % distal fall-off, and within 3 keV/µm at greater depths. Applying the MKM model to y∗, this process enables a microdosimetric RBE prediction with an agreement exceeding 98.5 %. CONCLUSION:This work represents a promising initial step toward the successful implementation of microdosimetry in routine clinical practice. Establishing a standardized approach will enhance consistency and comparability across institutions.

The adoption of silicon photomultiplier (SiPM) detectors over conventional photomultiplier tubes (PMTs) in Positron Emission Tomography (PET) has enhanced overall system performance. In this phantom study, small-lesion detectability was assessed for SiPM-based and PMT-based PET systems for various inhomogeneity sizes, acquisition times and activity contrasts between the inhomogeneity and background. Six spheres of internal diameters ranging between 4.0 mm and 13.0 mm were integrated into a NEMA/IEC PET Body Phantom and filled with fluorodeoxyglucose, with a sphere activity concentration of 29.2 MBq/L and five sphere-to-background activity concentration ratios between 4 and 20. Scans were performed with an SiPM-based system and a PMT-based PET system for each sphere-to-background activity concentration ratio for acquisition times between 1 and 10 min, and image reconstruction was performed with QClear for both systems. Reconstructed images were evaluated for lesion detectability by a lesion detectability index, contrast-to-noise ratio and lesion detectability Likert scales with validation by comparison with the Rose criterion. A model to estimate the acquisition time for each sphere to be detectable was derived and acquisition time was compared. The SiPM-based system demonstrated superior lesion detectability, identifying smaller and less active spheres with shorter acquisition times. For a sphere-to-background activity concentration ratio of 10 and a sphere internal diameter of 6.2 mm, the SiPM-based system achieved a contrast-to-noise ratio of 15.8 and a lesion detectability Likert score of 3, compared to 12.0 and 2, respectively, for the PMT-based system. The acquisition time of the SiPM-based system could be reduced by between 1.6

AIMS:Following the successful completion of a registry-based evaluation study of patients with extracranial oligometastatic disease or hepatocellular carcinoma treated with stereotactic ablative body radiotherapy (SABR), National Health Service (NHS) England and NHS Improvement funded an implementation and expansion programme in 2020 to increase SABR provision to 51 radiotherapy centres. This report details the integration of structured mentoring and radiotherapy quality assurance (RT QA) as core components for a safe and effective national SABR implementation programme. MATERIALS AND METHODS:Six members of the UK SABR Consortium developed a framework for effective mentoring that experienced SABR centres could follow to mentor those with limited or no experience. In parallel, the National Radiotherapy Trials Quality Assurance Group delivered an accreditation programme for completion by those centres comprising a facility questionnaire, contouring and planning benchmarks, end-to-end dosimetry audit and individual case review. RESULTS:Sixteen experienced centres mentored thirty-three new SABR sites, covering a range of techniques and equipment. A large multidisciplinary team of 25 individuals, consisting of clinical oncologists, medical physicists and therapeutic radiographers developed and delivered the RT QA programme. As of April 2025, all centres are accredited for lung, bone and nodes; the programme for the remaining anatomical sites is ongoing. Nearly 24,000 patients have been treated since the NHSE 2020 programme commenced. CONCLUSION:This is the first nationally funded programme demonstrating how structured mentorship and RT QA have been beneficial in the safe, effective and timely implementation of SABR services in England. The programme, developed through a multi-professional inter-group collaboration of SABR experts, ensured that radiotherapy centres were trained and supported to deliver consistent, high-quality SABR.

As a component of myeloablative conditioning before allogeneic hematopoietic stem cell transplantation (HSCT), Total Body Irradiation (TBI) is employed in radiotherapy centers all over the world. In recent and coming years, many centers are changing their TBI setup to a conformal isocentric technique, providing superior homogeneity and control of the target prescription dose, and more freedom for individualized organ-at-risk sparing or dose escalation. Also, more specifically bone-marrow- and/or lymphatics-targeted therapies such as Total Marrow (+ Lymphoid) Irradiation (TMI / TMLI), and Total Lymphoid Irradiation (TLI) are established and prospectively evaluated in several centers. With each center developing their own methods, a new practice heterogeneity is arising, as was the case for decades with conventional TBI. To provide a ground base - and therefore more options for more homogeneous and comparable practice - for centers who are implementing conformal isocentric techniques, a group of early adopters of isocentric conformal TBI and TM(L)I came together to convey issues they encountered during clinical implementation, and form consensus recommendations for delineation and planning targets, based on available literature evaluation and shared experience. These recommendations follow previously published recommendations regarding technical setup of conformal isocentric TBI / TM(L)I techniques.

Radiobiology relies on animal studies to demonstrate efficacy and safety of treatments. For proton-based studies in clinical settings, bespoke solutions, enabling animal irradiations without compromising health and safety regulations, need to be developed to facilitate the research. This study aims to demonstrate the usability of the IRRAMICE, a novel system with bespoke collimators to effectively treat small targets, within proton clinical facilities. Following a clinical workflow of planning CT, treatment plan design and delivery, a dosimetric evaluation of the IRRAMICE was conducted. Traceable absorbed dose was determined by measurements with (i) ion chamber, (ii) alanine pellets within a mouse phantom and a bespoke holder in the IRRAMICE, and (iii) Gafchromic film in the holder for a relative evaluation of the collimation system. Dose determined with alanine pellets in the mouse phantom were within 2% of the planned dose. The 2%/2 mm local gamma analysis of the dose distribution of the collimated beam spot determined by the film and the treatment planning system showed an average 98.3% passing rate. Through measurements in mouse phantoms, IRRAMICE demonstrated to be a suitable device for enabling the setup and delivery of treatment plans in a reliable and reproducible manner, to facilitate in vivo preclinical experiments.

Background: In 2021, a Technical Meeting was hosted by the International Atomic Energy Agency (IAEA) where it was recommended that a standardized method for assessing the accuracy of film dose calculations should be established. Purpose: To design an audit that evaluates the accuracy of film dosimetry processes. To propose a framework for identifying out-of-tolerance results and to perform an international pilot study to test the audit design. Methods: Six members of an international Dosimetry Audit Network (DAN) developed an audit for radiochromic film dosimetry. A single host center provided the materials to each participating DAN member to conduct the audits. Materials included: (1) a set of two irradiated audit films (10 Sq: 10 cm x 10 cm, 15 Sq: 15 cm x 15 cm), (2) a reference calibration film set, and (3) a blank sheet of film. The participants were blinded to the dose and tasked with producing dose maps using their standard film dosimetry process. Average Region-Of-Interest (ROI: 2 cm x 2 cm) dose was measured from the dose maps and compared to the known dose. In the audit, all participants used their local scanning and software protocols. Film calibration was performed in two distinct ways: (1) using a calibration film set which was provided by the host center and (2) using a calibration film set which was locally irradiated. Several variations of the audit were also performed to examine how scanning and software processing can affect film dosimetry results. In the first variation of the audit (VariantA), a set of film scans was processed using five different software solutions. In the second variation of the audit (VariantB), all films were scanned on the same scanner and processed using two in-house software solutions. Results: Taking one film scan from each participant, the standard deviations (1 sigma) (SD) in the dose returned from the host calibration and returned from the local calibration were +/- 7.2% and +/- 6.5% respectively, with variations from -12.4% to 12.9% of the known dose. The larger dose variations in the data set were attributed to the corrections applied for variations in scanner brightness during processing and incorrectly assigned calibration doses. When the raw image data set was processed by an expert user of each software solution (VariantA) the SDs were +/- 2.7% and +/- 3.7% for in-house and vendor-based software, respectively. When the films were scanned on a single scanner and processed with the two in-house software solutions (VariantB) the results had a SD of +/- 2.3%. Conclusions: An audit has been designed and tested for radiotherapy film dosimetry at an international level. A framework for diagnosing issues within a film dosimetry process has been proposed that could be used to audit centers that use film as a dosimeter. Incorporating quality assurance throughout the film process is important in obtaining accurate and consistent film dosimetry. A better understanding of vendor-based software systems is necessary for users to process accurate and consistent film dosimetry.

Background and purpose:Multi-leaf collimators (MLCs) with tilted leaf sides have a complex transmission behaviour that is not easily matched by radiotherapy treatment planning systems (TPSs). We sought to develop an MLC model that can accurately match test fields and clinically relevant plans at different centres.Materials and methods:Two new MLC models were developed and evaluated within a research version of a commercial TPS. Prototype I used adjusted-constant transmissions and Prototype II used variable transmissions at the tongue-and-groove and leaf-tip regions. Three different centres evaluated these prototypes for a tilted MLC and compared them with their initial MLC model using test fields and patient-specific quality-assurance measurements of clinically relevant plans. For the latter, gamma passing rates (GPR) at 2 %/2mm were recorded.Results:For the prototypes the same set of MLC parameters could be used at all centres, with only a slight adjustment of the offset parameter. For centres A and C, average GPR were >95 % and within 0.5 % GPR difference between the standard, and prototype models. In center B, prototypes I and II improved the agreement in clinically relevant plans, with an increase in GPR of 2.3 % ± 0.8 % and 3.0 ± 0.8 %, respectively.Conclusions:The prototype MLC models were either similar or superior to the initial MLC model, and simpler to configure because fewer trade-offs were required. Prototype I performed comparably to the more sophisticated Prototype II and its configuration can be easily standardized, which can be useful to reduce variability and improve safety in clinical practice.