PURPOSE:Diagnostic Reference Levels (DRLs) are benchmarks for optimizing radiation doses in medical imaging. This study establishes new national DRLs (NDRLs) for PET/CT examinations in Switzerland based on a multicentre survey. METHODS:Administered activities for PET examinations and dose indicators for localization / attenuation correction (AC) CT scans were collected in Swiss nuclear medicine (NM) institutes between April and September 2025. RESULTS:Data from 45 PET devices in 35 NM institutes were analysed (100% response). New NDRLs were defined as administered activitiesfor nine PET examinations: general oncology with [18F]FDG (3.1 MBq/kg; 220 MBq), prostate cancer imaging with [18F]F-PSMA (3.1 MBq/kg; 260 MBq), neuroendocrine tumour imaging with [68Ga]Ga-DOTA (2.1 MBq/kg; 160 MBq), brain tumour imaging with [18F]FET (3.0 MBq/kg; 200 MBq), inflammation/infection with [18F]FDG (3.3 MBq/kg; 230 MBq), neurological examinations with [18F]FDG (2.9 MBq/kg; 200 MBq) and [18F]flutemetamol (2.8 MBq/kg; 185 MBq), parathyroid imaging with [18F]fluorocholine (2.8 MBq/kg; 200 MBq), and myocardial perfusion with [82Rb]rubidium chloride (8.6 MBq/kg; 630 MBq/injection). Updated volume computed tomography dose index (CTDIvol) and dose-length product (DLP) for four AC CT were defined for vertex to mid-thighs (3.8 mGy/410 mGy·cm), vertex to feet (3.8 mGy/680 mGy·cm), brain (6.1 mGy/150 mGy·cm) and cardiac scans (1.3 mGy/40 mGy·cm). CTDIvol for AC CT varied considerably among NM institutes (1.0 - 7.5 mGy for vertex to mid-thighs), indicating potential for protocol optimization and standardization. The established NDRLs tended to be lower than international reference levels, and the corresponding dosimetric indices were generally low. CONCLUSION:The survey provides an overview of administered activities and CT doses in adult PET/CT examinations in Switzerland and establishes new NDRLs to guide protocol optimization.
AIM:This study evaluates the performance of the Siemens Biograph Trinion EP2 whole-body PET/CT system according to the NEMA NU2-2018 standard. METHODS:Following the NEMA NU2-2018 standard, spatial resolution was measured using a 22Na point source in air, sensitivity was calculated from consecutive measurements of a 18F containing line source surrounded by aluminum tubes, count rate performance, accuracy of corrections assessment and TOF resolution was based on measurements of an 18F line-source inside scatter phantom. PET-CT co-registration accuracy was assessed by radioactive and radiation dense point sources, image quality was evaluated using a NEMA IQ phantom. Measurements were done using implemented NEMA NU2-2018 acquisition protocols on a Siemens Biograph Trinion EP2 PET/CT system. RESULTS:The Trinion EP2 showed a spatial resolution between 4.0 and 4.4 mm FWHM at the center of the FOV. Sensitivity was measured with 13.8 kBq/MBq and the peak noise equivalent count rage of 143 kcps measured at 14.8 kBq/mL with a corresponding scatter fraction of 37.5%. The maximum average error was 1.6% between 1 kBq/mL and 14.8 kBq/mL and a TOF resolution of 241 ps was measured at a clinical activity concentration. Contrast recoveries between 47.2% and 81.6% were measured in the image quality phantom when using standard reconstructions. CONCLUSION:The Biograph Trinion EP2 PET/CT system shows a good overall performance providing a decent image quality comparable to state-of-the-art PET/CT systems with standard axial FOV between 20 and 30 cm.
PURPOSE:To present a transparent, physics-based, and generalisable calculation framework to predict the optimal rotational adjustment of toric supplementary intraocular lenses (SIOLs), comprising toric phakic intraocular lenses implanted in the phakic eye and toric AddOn (secondary sulcus-fixated) lenses implanted in the pseudophakic eye, quantifying the expected refractive benefit across four corneal models. METHODS:A paraxial vergence-based calculation framework was implemented to predict the optimal toric axis of a misaligned SIOL. Required inputs were the measured manifest refraction at spectacle plane, corneal power (using either thin- or thick-cornea models), labelled equivalent and toric power of the SIOL, measured SIOL axis, and axial SIOL position. The effective lens position was estimated by combining the measured back-vertex position with an offset between the back-vertex plane and the image-sided principal plane, derived from legacy phakic lens design data or custom template SIOL models. Forward and backward spherocylindrical vergence transformations were embedded in a nonlinear sequential quadratic programming optimisation to identify the SIOL axis that minimised residual refractive cylinder. The method was demonstrated in four representative clinical scenarios, including phakic, pseudophakic , keratoplasty, and prior laser vision correction eyes. RESULTS:In all examples, the model predicted a specific rotational adjustment of the SIOL (16-18°) that substantially reduced refractive cylinder. Absolute reductions ranged from 1.7 to 2.4 D, corresponding to relative cylinder reductions of 67-94%. The framework successfully accommodated different corneal models and lens types, and provided predicted postoperative refraction and quantitative performance metrics. CONCLUSIONS:This framework enables individualised planning of toric SIOL realignment across diverse corneal models and lens geometries. Explicitly defining optical assumptions and vergence transformations allows reproducible prediction of both optimal rotation and expected refractive benefit using routine clinical inputs. Prospective clinical validation is warranted.
X-ray multimeters (XMMs) are widely used for quality control measurements in mammography, providing air kerma, half-value layer (HVL), and tube voltage from a single exposure. The energy dependence of their response was comprehensively investigated for various anode/filter combinations and software selections. However, the influence of a change in the X-ray spectrum due to additional material in the beam has not yet been systematically investigated. The aim of this study is to quantify the sensitivity of XMM calibration coefficients to changes in X-ray spectra introduced by additional polymethyl methacrylate (PMMA) of different thicknesses. Four commercially available XMMs were calibrated at the IAEA dosimetry laboratory for air kerma, HVL, and tube voltage using two anode/filter combinations (Mo/Mo and W/Al) at tube voltages ranging from 25kV to 35kV. Calibration coefficients were determined without additional filtration and with PMMA thicknesses of 2.0mm, 2.8mm, and 4.8mm placed close to the X-ray tube to modify the primary spectrum while minimizing scattered radiation reaching the detectors. In relation to the calibration coefficient determined without PMMA deviations of up to 11% were observed for air kerma rate. HVL and tube voltage calibration coefficients exhibited substantially larger deviations, reaching up to 37% and 42%, respectively. We conclude that changes in the X-ray spectra as from additional PMMA filtration, can substantially alter XMM calibration coefficients, particularly for HVL and tube voltage measurements. XMM responses are highly sensitive to spectral modifications beyond standard anode/filter combinations and tube voltage settings.
PURPOSE:The novel HyperSight cone-beam CT (CBCT) system (Varian Medical Systems, Siemens Healthineers, Palo Alto, USA) provides image quality comparable to native CT and offers advantages for contouring in online-adaptive radiotherapy. However, daily imaging increases organ dose. This study evaluates and compares organ doses across HyperSight protocols on an O-ring Linac and calculates the effective dose and secondary cancer risk associated with daily imaging. METHODS:Thermoluminescent dosimeter (TLD) measurements were performed on an anthropomorphic phantom for all pre-configured CBCT protocols in HyperSight, with TLDs placed according to each entity (head, head and neck, thorax, chest, and pelvis). The resulting imaging doses were compared across the various protocols and TLD positions, followed by the calculation of effective doses and the associated secondary cancer risk. RESULTS:HyperSight CBCT demonstrated lower organ doses compared with previous systems. Mean bladder and rectum dose was 10mGy versus 27mGy for OBI Version 1.4.13, while mean head dose was 2mGy compared with 1.2mGy for Halcyon 3.0. A left-right dose asymmetry was observed due to partial gantry rotation, resulting in higher exposure in beam-facing organs. Imaging dose varied considerably between protocols. Low Dose protocols reduced exposure by up to 55%, whereas slow and large protocols increased dose by 40-60%. CONCLUSION:HyperSight provides high-quality imaging with lower dose levels than previous CBCT generations. The observed beam geometry-related asymmetry should be considered in clinical use, and individualized protocol selection is essential to minimize unnecessary exposure in image guided and adaptive radiotherapy under ALARA principles.
Particle-based radiotherapy, including proton therapy, heavy-ion therapy, and boron neutron capture therapy (BNCT), enables conformal dose delivery but introduces model-dependent biological-dose uncertainty. This uncertainty reflects variations in relative biological effectiveness (RBE), linear energy transfer (LET), oxygenation, microdosimetric spectra, and boron distribution, so identical nominal prescriptions may not yield equivalent biological effects. This review summarizes representative clinical, secondary-review, and investigational model families, including fixed and variable-RBE proton models, the local effect model (LEM) and microdosimetric kinetic model (MKM) families for heavy ions, and compound biological effectiveness (CBE), photon-isoeffective-dose, microdosimetric, and nanodosimetric BNCT frameworks. We compare their assumptions, input descriptors, validation status, clinical readiness, and implementation barriers. We further distinguish prescription-embedded clinical systems from secondary-review models and investigational mechanistic frameworks to clarify the current level of clinical evidence supporting each model family. Published experimental and model-comparison studies indicate that proton RBE may increase in high-LET distal-edge regions, that LEM- and MKM-based carbon-ion systems can yield clinically relevant, site- and endpoint-dependent differences in RBE-weighted dose interpretation, and that BNCT biological dose is strongly affected by component-dose and boron-distribution assumptions. We propose an evidence-informed four-layer harmonization perspective, rather than a formal consensus guideline, consisting of minimum reporting, reference mapping, model-sensitivity quality assurance (QA), and registry-based clinical learning.
BACKGROUND:This study examined how intracochlear voltage distributions obtained from impedance field telemetry (IFT) in cochlear implant (CI) users with straight lateral wall electrodes related to electrically evoked cervical and ocular vestibular myogenic responses (e-cVEMPs and e-oVEMPs). METHODS:e-cVEMPs and e-oVEMPs were recorded in adult MED-EL Synchrony CI users by stimulating at intracochlear electrodes E3, E6, E10 and E11. IFT provided voltage matrices characterizing intracochlear electric field distribution. Voltage data were adjusted using a current-dependent scaling factor to account for stimulation-level differences, and both qualitative and quantitative analyses were performed to compare participants with and without e-VEMP responses and to assess spatial dependencies between voltage profiles and vestibular activation. RESULTS:The study included 18 implanted ears of 17 participants. Qualitative evaluation of the difference matrices across all stimulation electrodes revealed local variations within individual stimulation sites, but no consistent group-specific pattern that persisted across electrodes for either e-cVEMPs or e-oVEMPs. Quantitative analysis of voltage line graphs showed higher voltages and e-oVEMP thresholds across all sites in participants with e-oVEMPs, reaching significance only at E3. For e-cVEMPs, analysis showed no significant group differences. Detection rates demonstrated a spatial trend, with e-cVEMPs occurring predominantly during basal stimulation and e-oVEMPs during apical stimulation. CONCLUSION:These data suggest that there could be different current pathways for saccular and utricular co-stimulation. Intracochlear electric field distributions could not be directly correlated with e-VEMP occurrence. Spatial dependencies and voltage decay patterns suggest separate mechanisms, possibly related to differences in local field orientation and tissue conductivity, which have to be further examined with respect to anatomical data.
PURPOSE:To examine whether mono-exponential individual fitting (Mono-IFIT) is an adequate reference model for validating single-time-point (STP) renal dosimetry in [177Lu]Lu-PSMA-617 therapy, and to compare the resulting STP accuracy rankings with those obtained using population-based model selection with non-linear mixed-effects modelling (PBMS NLMEM). METHODS:Kidney biokinetic data were analysed using a training dataset of 500 virtual patients generated from a six-parameter sum-of-exponentials function previously identified within the PBMS NLMEM framework, and an external testing dataset comprising 10 clinical patients with low-volume metastatic hormone-sensitive prostate cancer. Reference absorbed doses were calculated with Mono-IFIT and PBMS NLMEM. Four STP methods (STPNLMEM, STPMLR, STPH, and STPM) were evaluated at (47.7±2.2) h post-injection. Accuracy was assessed using relative deviation (RD), mean absolute percentage error (MAPE), and root mean square error (RMSE). RESULTS:The selected PBMS NLMEM model provided a better description of the renal time-activity data than Mono-IFIT according to predefined goodness-of-fit criteria and Akaike-weight-based model selection. STP performance rankings depended strongly on the chosen reference model. Against Mono-IFIT, STPM and STPH showed the smallest deviations (mean RD -2.3% and 3.3%; MAPE 3.5% and 4.5%; RMSE 4.6% and 5.3%, respectively), whereas STPNLMEM showed the largest deviation (mean RD 16.0%; MAPE 16.0%; RMSE 17.9%). Against PBMS NLMEM, STPNLMEM showed the closest agreement (mean RD -2.5%; MAPE 6.6%; RMSE 9.3%), whereas STPMLR, STPH and STPM underestimated absorbed dose (mean RD -14.1%, -13.1% and -17.8%; MAPE 15.2%, 13.1% and 17.8%; RMSE 17.3%, 14.8% and 19.1%, respectively). CONCLUSION:The apparent accuracy of STP methods is highly dependent on the reference model. For [177Lu]Lu-PSMA-617 renal dosimetry, Mono-IFIT should not be considered the preferred reference for method validation. In this dataset, PBMS NLMEM provided the better reference framework, and STPNLMEM showed the closest agreement with it. To ensure broader applicability, this approach should also be evaluated for salivary glands and tumours, which may require tailored fitting strategies, thereby supporting the development of a generalisable STP method for personalised treatment. Prospective validation in larger cohorts remains necessary.
Long-range resistance (Rt) reflects the resistive component of current flow through intracochlear fluids, surrounding tissues, and bone before it returns to the extracochlear return electrode (RE). Unlike near-field resistances, which mainly capture the local tissue-electrode interface, Rt captures the global tissue pathway and therefore represents how efficiently stimulation current spreads throughout the cochlea and surrounding anatomical structures. In this study, we have determined the long-range resistance (Rt) between a stimulation electrode (SE) and the extracochlear RE from precision impedance spectroscopic measurements in three human cadaveric heads involving six sequentially cochlear implanted ears with the MED-EL FLEX28 and the Cochlear Ltd. CI622 electrode arrays. Equivalent electrical circuit (EEC) modelling, combined with finite element method (FEM)-based correction, was employed to separate the biological impedance components from non-biological artefacts arising from the measurement setup. Principal Component Analysis (PCA) was applied to detect and remove atypical impedance responses due to malfunctioning electrodes. Missing electrode values were interpolated using cubic splines to maintain continuity. Across both array types, Rt consistently increased from basal to apical electrode positions, consistent with the progressively smaller scala tympani cross-section in the apical turn. The overall trend of Rt observed in the present study also aligns with trends reported in in vivo telemetry studies, supporting the translational relevance of the measurements.
INTRODUCTION:Guidelines on how to perform patient-specific quality assurance (PSQA) in stereotactic radiotherapy (SRT) are currently not available. In this context, guidelines for modulated techniques like IMRT or IMAT do include descriptions of PSQA. However, commonly used quality assurance (QA) devices, methods, and evaluation metrics are not sufficiently suitable for small-field conditions. Consequently, these guidelines cannot generally be applied to stereotactic radiotherapy. The aim of this work is to assess the limitations of current clinical practice and provide guidance on choosing QA methods given the extensive QA requirements. Additionally, we will present a method for evaluating comprehensive PSQA programs, identifying blind spots, and supporting the selection of suitable devices and methods to overcome them. METHODS/RESULTS:We reviewed available literature, especially guidelines, and identified main issues in today's PSQA practice for SRT by performing surveys among users and vendors. Current QA equipment, software, and methods were assessed and analyzed. Independently, we defined the scope of an appropriate PSQA for SRT. Subsequently, we related this to available devices and methods in a vendor-neutral manner, resulting in a toolkit for evaluation of site-specific PSQA programs in SRT. The approach and result were reviewed by a group of experts. DISCUSSION/CONCLUSION:No single QA solution or method can account for all PSQA needs for SRT. In addition, properly choosing PSQA evaluation metrics is key for a meaningful verification process. The heterogeneity of SRT implementations throughout different sites encompasses different needs and hinders the creation of a static guideline. In the absence of such, we derived a best option decision-making toolkit for optimizing a PSQA program to be used in the environment of stereotactic radiotherapy.
Positron Emission Tomography (PET) is a non-invasive, highly sensitive functional imaging modality, firmly established in clinical practice for the diagnosis and assessment of therapeutic efficacy in oncological and neurological disorders. Recent advances in digital image processing, sensor technology, and imaging algorithms have enabled this technique to achieve sub-millimetric spatial resolution and a high degree of compactness, thereby making its application to the investigation of biological systems smaller than humans both feasible and scientifically meaningful. In this review, we detail the substantial impact of PET on emerging applications in biomedicine, food security, and agriculture. We focus specifically on non-conventional implementations of PET, including small-animal imaging in species beyond traditional murine models, and imaging of crops. The discussed translational pathways of PET - from bench to bedside and from-lab-to-field - impose stringent technological requirements on system design and performance, thereby driving further innovation in PET detector technologies and associated electronics.
BACKGROUND:This study focuses on evaluating how SubtlePET™, an artificial intelligence (AI)-based image enhancement algorithm, produced PET/CT images compare against EARL Standard-2 harmonized images, and to assess its impact on quantitative accuracy and workflow in a clinical setting. METHODS:A NEMA IEC PET Body Phantom with 10:1 (EARL protocol) and 4:1 (NEMA NU2-2018 protocol) sphere-to-background ratios were scanned using a General Electric Discovery™ IQ Gen-2 PET/CT system. Data were acquired in list mode for 10 minutes per bed position and retrospectively reconstructed to simulate reduced scan duration. Images were reconstructed with and without SubtlePETTM (phantom image trained) using EARL Standard-2 accredited reconstruction. Recovery coefficients (SUVmean,max,peak) were calculated and compared to EARL standard-2 along with their repeatability. Additionally, 23 patient datasets acquired for 3-minutes per bed-position were reconstructed to simulate reduced acquisition time both by SubtlePETTM (human image trained) and EARL Standard-2 reconstruction parameters. Lesions were segmented semi-automatically to assess SUV and volume metrics. Statistical comparisons were performed using a two-sample t-test assuming equal variances. RESULTS:SubtlePETTM reconstructions achieved 91% compliance with EARL standard-2. SUVpeak remained the most robust metric across scan duration. Patient data showed no significant differences in SUVpeak or volume for SubtlePETTM at half the acquisition time. Minor deviations were noted in SUVmax and SUVmean for smaller lesions at 1-min/bed. CONCLUSION:SubtlePET™ preserves quantitative performance comparable to EARL Standard 2-compliant reconstructions, particularly when SUVpeak is used, although deviations associated with reduced acquisition time persist. These findings support the potential for reduced scan duration, which may facilitate lower radiation exposure or increased patient throughput without compromising diagnostic quality. Further validation across different scanners and clinical settings is warranted.
Analysis of dynamic phosphorus magnetic resonance spectroscopy (31P MRS) data is often hindered by variability in data quality. A quality control (QC) pipeline developed by Naëgel (2023) introduced six key parameters to ensure reliable 31P MRS results in large clinical datasets. This study tested the transferability of this QC scoring (QCS_REF) to two different research sites equipped with 3T and 7T MR systems and different ergometers. Twelve groups with the focus on frail and elderly subjects and patients with neurodegenerative diseases were included. The application of QCS_REF limits led to the improvement of the statistical power in some patient groups, but to the exclusion of substantial data for all our groups and experimental settings at both 3T and 7T. Only 28% of all recovery and exercise period data at 3T and 21% at 7T passed QCS_REF inclusion criteria. Therefore, two new sets of quality control criteria, QCS1 and QCS2, were proposed, reflecting achieved SNR of individual MR signalsand the patient phenotype included. We showed that the transferability of the QCS_REF did not depend on the magnetic field, the coil, or localization scheme. The new QCS did not significantly influence the mean recovery and exercise time constants of each group compared to QCS_REF. We verified that six proposed key parameters were adequate for an objective assessment of the quality of dynamic 31P MRS measurement at 3T as well as 7T. However, the patient group characteristics and experimental set-up significantly affect the ability to meet dynamic 31P MRS quality control thresholds, supporting the use of flexible QC criteria for robust data acquisition across diverse clinical populations.
PURPOSE:To study the impact of transferring a treatment plan between two machines on the delivered dose, new complexity metrics based on Leaf Opening and Closing Times (LOT and LCT) were developed. MATERIALS AND METHODS:Basic tomotherapy treatment plans were created to identify the ranges of LOT that are accurately delivered and those that deviate from the planned values. Newly developed complexity metrics were derived from these ranges. These metrics from 103 clinical plans and 6 phantom plans were analyzed to identify treatment sites affected by short LCTs during plan transfer. A software tool was developed to estimate the additional dose associated with short LCTs, and these estimations were verified by measurements. RESULTS:Opening time deviations were observed for short LOTs (below 50 ms) and short (but non-zero) LCTs (up to 40 ms). When a plan is created, no LOTs are generated in these regions. However, when a plan is transferred between two machines (e.g., in case of a breakdown), a fraction of LOTs equal to LOTmax (i.e., with no leaf closing) are converted into short LCTs. The additional dose due to these short LCTs could reach up to 3%. Affected treatment sites included pelvis, anal canal, and bone metastases. Measured dose discrepancies were consistent with estimations, with mean errors of 0.3% for phantom plans and 0.6% for clinical plans. Using an alternative transfer method, mean dose discrepancies decreased from 3% to less than 1% for all plans. CONCLUSIONS:To date, transferring Tomotherapy plans increases LOT distribution complexity by creating short LCTs. The additional dose due to short LCTs is significant for plans with high gantry rotation speed and "hockey stick" shaped LOTs distributions. An alternative transfer method can reduce delivery errors by eliminating short LCTs.
In diagnostic radiology, it is essential to ensure that image quality is sufficiently good to support accurate diagnosis and patient safety. This is in accordance with the ALARA principle of keeping radiation exposure as low as reasonably achievable - taking into account economic and societal factors. Further, the detection of subtle low-contrast differences is critical for early disease detection, particularly in cases such as liver metastases. Iterative reconstruction algorithms have improved medical imaging by reducing noise, but their non-linear nature challenges traditional assessment metrics. Model observers like the Channelized Hotelling Observer provide task-specific evaluations suitable for non-linear systems. This study employs a previously proposed method for determining the dose-averaged detectability in computed tomography (CT) systems, focusing on minimizing systematic errors from measurement processes and phantom specimen variations. We conducted two repeatability analyses: intra-specimen, using the same CT scanner and phantom, and inter-specimen, using different specimens of the same phantom type. The study utilized a GE Brightspeed 16 scanner. The analyses revealed significant variations among different specimens, necessitating corrections for consistent comparison. The main correction underscores the importance of experimental verification of actual contrast values for accurate determination of the figure of merit (FOM) with multiple phantom specimens.
Volumetric-modulated arc therapy (VMAT) treatment planning for lung tumors requires balancing adequate planning target volume (PTV) coverage with optimal organ-at-risk (OAR) sparing. However, plan quality varies due to differences in planner expertise, preferences, and especially patient anatomy. This study introduces a Comprehensive Plan Score (CPS) for lung VMAT plans, integrating geometry-based OAR quality indices derived from overlap volume histograms (OVH) and overlap-z-histograms (OZH).CPS was developed by combining normalized target and OAR scores, including geometry-based metrics derived from OVH and OZH. Relative weights were learned from blinded pairwise plan comparisons performed by four senior radiation oncologists (ROs). A total of 35 manual versus automated lung VMAT plan pairs were evaluated, with 20 cases used for training and 15 for independent testing.Across all comparisons, ROs expressed a clear preference in 81% of cases, while 19% were judged equivalent. Inter-observer agreement was fair (Fleiss’ κ = 0.36), with pairwise Cohen’s κ ranging from 0.13 to 0.71. In the independent test cohort, CPS using the preference-trained weighting set matched the ROs consensus in 11/15 cases. Applying an equivalence threshold (ΔCPS = 0.01) increased agreement to 13/15 cases (86%).In conclusion, the CPS provides a more objective and geometry-based measure of lung VMAT plan quality. By quantifying achievable OAR sparing based on prior data, it supports consistent and standardized plan evaluation, potentially improving the reproducibility and overall quality of radiotherapy planning.
Purpose: Aim of the study was to investigate DNA damage induction and repair in peripheral blood mononuclear cells (PBMCs) after internal ex vivo irradiation with short-lived radionuclides with varying emission properties.Methods: Blood samples from healthy volunteers were irradiated with different activity concentrations for 1 h, resulting in absorbed doses to the blood from nominally 3 to 100 mGy. DNA double-strand breaks (DSBs) in PBMCs were assessed by quantifying radiation-induced γ-H2AX+53BP1-positive foci (RIF). In part A of the study, four different radionuclides (177Lu, 90Y, 99mTc and 68Ga) were used to test for radionuclide dependence. In part B, blood samples were exposed to 177Lu and cells were fixed at three different time points (directly, 4 h and 24 h after irradiation) to investigate DSB repair and its dependence on the absorbed dose.Results: The number of RIF increases linearly with the absorbed dose to the blood, independent of the radionuclide used for irradiation. The decline in RIF after irradiation can be described by an exponential function, with a trend towards higher repair rates at higher absorbed doses to the blood, i.e. (0.20±0.12) h⁻1 for 25 mGy, (0.22±0.04) h⁻1 for 50 mGy, and (0.37±0.06) h⁻1 for 100 mGy.Conclusion: Our results show a clear relationship between absorbed dose and DSB foci induced by internal irradiation in blood cells, independent of the emission properties of the particular radionuclide used. A better understanding of DNA damage repair dynamics after internal irradiation can improve future nuclear medicine therapies.
Radioligand therapy targeting the prostate-specific membrane antigen (PSMA) or somatostatin receptors (sstr) has become an established treatment option for metastatic castration-resistant prostate cancer and advanced or inoperable neuroendocrine tumours, respectively. Although several studies have already demonstrated the clinical usefulness of dosimetry-guided personalized treatment schedules, and although there is growing evidence for absorbed-dose-effect-relationships, the clinical implementation of personalized dosimetry is slow due to various factors, such as logistical constraints, a lack of standardisation or missing reimbursement. This review highlights current and future developments in quantitative imaging and personalized dosimetry for radioligand therapy. Current challenges, such as improving the accuracy and efficiency of quantitative imaging, imaging of alpha emitters, single-time-point dosimetry and PET-based absorbed dose prediction, microdosimetry and radiobiology, will be considered. Further, this review will address current ideas on how to implement dosimetry-guided treatment planning for radioligand therapy.
Cochlear implants (CIs) are effective auditory neuroprostheses, but performance varies across patients. One factor contributing to this variability is the spread of electrical current within the cochlea, which reduces spectral resolution and limits speech understanding. Far-field resistance, which can be measured directly, reflects current flow through perilymph and surrounding tissue and may be influenced by patient-specific anatomy.We developed an image-based model to automatically predict far-field resistance profiles using patient-specific cochlear geometries derived from preoperative computed tomography (CT) scans. In a retrospective analysis of 36 CI cases, surface meshes of the scala tympani and scala vestibuli were automatically segmented. Electrode positions were extracted from postoperative CT scans for validation purposes. Far-field resistance was estimated by computing cumulative resistances along longitudinal pathways within the scalae. The model systematically overestimated resistances by up to a factor of 5.2 depending on electrode insertion depth. After systematic deviation correction, high agreement with measured values was achieved in 33 of 36 subjects (root mean square error less than 0.15 kΩ, Spearman ρ=0.83), while outliers suggested atypical current spread due to electrode positioning, tissue contact, or alternative conductive pathways. The image-based model captured subject-specific resistance trends and apical electrode variability better than a group-average reference, though basal predictions were affected by near-field contributions and segmentation uncertainties.These results demonstrate that individualized CT-based modeling can approximate far-field resistance profiles and could enable further research on the interpretation of intracochlear current flow. Our approach could use routinely acquired preoperative imaging to complement the measured resistance, enabling the interpretation of inter-subject variability and the identification of atypical profiles potentially related to electrode positioning or tissue changes. The approach could be integrated into clinical workflows and extended with advanced modeling techniques to support surgical planning, postoperative monitoring, and device programming, linking anatomical imaging with functional impedance assessment.
