PURPOSE:Monte Carlo modelling of SPECT imaging in Molecular Radiotherapy can improve activity quantification. Until now, SPECT modelling with GATE only considered circular orbit (CO) acquisitions. This cannot reproduce auto-contour acquisitions, where the detector head moves close to the patient to improve image resolution. The aim of this work is to develop and validate an auto-contouring step-and-shoot acquisition mode for GATE SPECT modelling. METHODS:177Lu and 131I SPECT experimental acquisitions performed on a Siemens Symbia T2 and GE Discovery 670 gamma camera, respectively, were modelled. SPECT projections were obtained for a cylindrical Jaszczak phantom and a lung and spine phantom. Detector head parameters (radial positions and acquisition angles) were extracted from the experimental projections to model the non-circular orbit (NCO) detector motion. The gamma camera model was validated against the experimental projections obtained with the cylindrical Jaszczak (177Lu) and lung and spine phantom (131I). Then, 177Lu and 131I CO and NCO SPECT projections were simulated to validate the impact of explicit NCO modelling on simulated projections. RESULTS:Experimental and simulated SPECT images were compared using the gamma index, and were in good agreement with gamma index passing rate (GIPR) and gammaavg of 96.27%, 0.242 (177Lu) and 92.89%, 0.36 (131I). Then, simulated 177Lu and 131I CO and NCO SPECT projections were compared. The GIPR, gammaavg between the two gamma camera motions was 99.85%, 0.108 for 177Lu and 75.58%, 0.6 for 131I. CONCLUSION:This work thereby justifies the need for auto-contouring modelling for isotopes with high septal penetration.

Purpose: Monte Carlo modelling of SPECT imaging in Molecular Radiotherapy can improve activity quantifica-tion. Until now, SPECT modelling with GATE only considered circular orbit (CO) acquisitions. This cannot reproduce auto-contour acquisitions, where the detector head moves close to the patient to improve image resolution. The aim of this work is to develop and validate an auto-contouring step-and-shoot acquisition mode for GATE SPECT modelling.& nbsp;Methods: Lu-177 and I-131 SPECT experimental acquisitions performed on a Siemens Symbia T2 and GE Discovery 670 gamma camera, respectively, were modelled. SPECT projections were obtained for a cylindrical Jaszczak phantom and a lung and spine phantom. Detector head parameters (radial positions and acquisition angles) were extracted from the experimental projections to model the non-circular orbit (NCO) detector motion. The gamma camera model was validated against the experimental projections obtained with the cylindrical Jaszczak (Lu-177) and lung and spine phantom (I-131). Then, Lu-177 and I-131 CO and NCO SPECT projections were simulated to validate the impact of explicit NCO modelling on simulated projections.& nbsp;Results: Experimental and simulated SPECT images were compared using the gamma index, and were in good agreement with gamma index passing rate (GIPR) and gammaavg of 96.27%, 0.242 (177Lu) and 92.89%, 0.36 (131I). Then, simulated Lu-177 and I-131 CO and NCO SPECT projections were compared. The GIPR, gammaavg between the two gamma camera motions was 99.85%, 0.108 for Lu-177 and 75.58%, 0.6 for I-131.& nbsp;Conclusion: This work thereby justifies the need for auto-contouring modelling for isotopes with high septal penetration.

PurposeThe aim of this study was to quantitatively compare five commercial dosimetric software platforms based on the analysis of clinical datasets of patients who benefited from peptide receptor radionuclide therapy (PRRT) with 177Lu‐DOTATATE (LUTATHERA®).MethodsThe dosimetric analysis was performed on two patients during two cycles of PRRT with 177Lu. Single photon emission computed tomography/computed tomography images were acquired at 4, 24, 72, and 192 h post injection. Reconstructed images were generated using Dosimetry Toolkit® (DTK) from Xeleris™ and HybridRecon‐Oncology version_1.3_Dicom (HROD) from HERMES. Reconstructed images using DTK were analyzed using the same software to calculate time‐integrated activity coefficients (TIAC), and mean absorbed doses were estimated using OLINDA/EXM V1.0 with mass correction. Reconstructed images from HROD were uploaded into PLANET® OncoDose from DOSIsoft, STRATOS from Phillips, Hybrid Dosimetry Module™ from HERMES, and SurePlan™ MRT from MIM. Organ masses, TIACs, and mean absorbed doses were calculated from each application using their recommendations.ResultsThe majority of organ mass estimates varied by <9.5% between all platforms. The highest variability for TIAC results between platforms was seen for the kidneys (28.2%) for the two patients and the two treatment cycles. Relative standard deviations in mean absorbed doses were slightly higher compared with those observed for TIAC, but remained of the same order of magnitude between all platforms.ConclusionsWhen applying a similar processing approach, results obtained were of the same order of magnitude regardless of the platforms used. However, the comparison of the performances of currently available platforms is still difficult as they do not all address the same parts of the dosimetric analysis workflow. In addition, the way in which data are handled in each part of the chain from data acquisition to absorbed doses may be different, which complicates the comparison exercise. Therefore, the dissemination of commercial solutions for absorbed dose calculation calls for the development of tools and standards allowing for the comparison of the performances between dosimetric software platforms.

PurposeSmall‐scale dosimetry studies generally consider an artificial environment where the tumors are spherical and the radionuclides are homogeneously biodistributed. However, tumor shapes are irregular and radiopharmaceutical biodistributions are heterogeneous, impacting the energy deposition in targeted radionuclide therapy. To bring realism, we developed a dosimetric methodology based on a three‐dimensional in vitro model of follicular lymphoma incubated with rituximab, an anti‐CD20 monoclonal antibody used in the treatment of non‐Hodgkin lymphomas, which might be combined with a radionuclide. The effects of the realistic geometry and biodistribution on the absorbed dose were highlighted by comparison with literature data. Additionally, to illustrate the possibilities of this methodology, the effect of different radionuclides on the absorbed dose distribution delivered to the in vitro tumor were compared.MethodsThe starting point was a model named multicellular aggregates of lymphoma cells (MALC). Three MALCs of different dimensions and their rituximab biodistribution were considered. Geometry, antibody location and concentration were extracted from selective plane illumination microscopy. Assuming antibody radiolabeling with Auger electron (125I and 111In) and β− particle emitters (177Lu, 131I and 90Y), we simulated energy deposition in MALCs using two Monte Carlo codes: Geant4‐DNA with “CPA100” physics models for Auger electron emitters and Geant4 with “Livermore” physics models for β− particle emitters.ResultsMALCs had ellipsoid‐like shapes with major radii, r, of ~0.25, ~0.5 and ~1.3 mm. Rituximab was concentrated in the periphery of the MALCs. The absorbed doses delivered by 177Lu, 131I and 90Y in MALCs were compared with literature data for spheres with two types of homogeneous biodistributions (on the surface or throughout the volume). Compared to the MALCs, the mean absorbed doses delivered in spheres with surface biodistributions were between 18% and 38% lower, while with volume biodistribution they were between 15% and 29% higher. Regarding the radionuclides comparison, the relationship between MALC dimensions, rituximab biodistribution and energy released per decay impacted the absorbed doses. Despite releasing less energy, 125I delivered a greater absorbed dose per decay than 111In in the r ~ 0.25 mm MALC (6.78·10−2 vs 6.26·10−2 µGy·Bq−1·s−1). Similarly, the absorbed doses per decay in the r ~ 0.5 mm MALC for 177Lu (2.41·10−2 µGy·Bq−1·s−1) and 131I (2.46·10−2 µGy·Bq−1·s−1) are higher than for 90Y (1.98·10−2 µGy·Bq−1·s−1). Furthermore, radionuclides releasing more energy per decay delivered absorbed dose more uniformly through the MALCs. Finally, when considering the radiopharmaceutical effective half‐life, due to the biological half‐life of rituximab being best matched by the physical half‐life of 177Lu and 131I compared to 90Y, the first two radionuclides delivered higher absorbed doses.ConclusionIn the simulated configurations, β− emitters delivered higher and more uniform absorbed dose than Auger electron emitters. When considering radiopharmaceutical half‐lives, 177Lu and 131I delivered absorbed doses higher than 90Y. In view of real irradiation of MALCs, such a work may be useful to select suited radionuclides and to help explain the biological effects.

BACKGROUND The SR101 N-(3-[18F]Fluoropropyl) sulfonamide ([18F]SRF101) is a Sulforhodamine 101 derivative that was previously synthesised by our group. The fluorescent dye SR101 has been reported as a marker of astroglia in the neocortex of rodents in vivo. OBJECTIVE The aim of this study was to perform a toxicological evaluation of [18F]SRF101 and to estimate human radiation dosimetry based on preclinical studies. METHODS Radiation dosimetry studies were conducted based on biokinetic data obtained from a mouse model. A single-dose toxicity study was carried out. The toxicological limit chosen was <100 μg, and allometric scaling with a safety factor of 100 for unlabelled SRF101 was selected. RESULTS The absorbed and effective dose estimated using OLINDA/EXM V2.0 for male and female dosimetric models presented the same tendency. The highest total absorbed dose values were for different sections of the intestines. The mean effective dose was 4.03 x10-3 mSv/MBq and 5.08 x10-3 mSv/MBq for the male and female dosimetric models, respectively, using tissue-weighting factors from ICRP-89. The toxicity study detected no changes in the organ or whole-body weight, food consumption, haematologic or clinical chemistry parameters. Moreover, lesions or abnormalities were not found during the histopathological examination. CONCLUSION The toxicological evaluation of SRF101 verified the biosafety of the radiotracer for human administration. The dosimetry calculations revealed that the radiation-associated risk of [18F]SRF101 would be of the same order as other 18F radiopharmaceuticals used in clinical applications. These study findings confirm that the novel radiotracer would be safe for use in human PET imaging.

Introduction: [C]Choline ([C]COL) has been widely used for prostate cancer diagnosis; however, this radiopharmaceutical is not recommended for patients with a low absolute PSA value (< 1 ng/mL) due to its limited sensitivity and specificity. The enzyme glycine N-methyltransferase is overexpressed during prostate cancer progression. It catalyses the methylation of glycine using S-adenosyl methionine (SAM or AdoMet) as a substrate. The authors have previously reported the automated radiosynthesis of [C]SAM as a potential agent in the diagnosis of aggressive prostate cancer. In this study, a biological and dosimetric evaluation of [C]SAM was performed. Results: The evaluation of [C]SAM in a control group of healthy mouse model showed a relatively high tracer uptake in the kidneys and a rapid blood clearance. Most activity was eliminated in the urine. In a PC3 prostate cancer xenograft tumour model, [C]SAM tumour uptake was significantly higher in relation to [C]COL.The human dosimetry of [C]SAM was estimated by extrapolating the preclinical results. The mean effective dose was 8.17 x 10 mSv/MBq and 2.49 x 10 mSv/MBq without and with bladder voiding, respectively. The results for kidneys in humans were comparable to those previously described for [C]COL. Conclusions: The PET/CT studies showed a statistically higher in vivo tumour uptake of [C]SAM compared to [C]COL for the cancer xenograft model. The absorbed dose estimations of major organs and the effective dose were determined. The results suggested that [C]SAM may be a potential PET tracer for prostate cancer diagnosis.

Introduction: The aim of this work was to study the biodistribution, metabolism and radiation dosimetry of rats injected with [F-18]FNM using PET/CT images. This novel radiotracer targeting NMDA receptor has potential for investigation for neurological and psychiatric diseases. Methods: Free fraction and stability in fresh human plasma were determined in vitro. PET/CT was performed on anesthetized rats. Organs were identified and 3D volumes of interest (VOls) were manually drawn on the CT in the center of each organ. Time activity curves (TACs) were created with these VOls, enabling the calculation of residence times. To confirm these values, ex vivo measurements of organs were performed. Plasma and urine were also collected to study in vivo metabolism. Data was extrapolated to humans, effective doses were estimated using ICRP-60 and ICRP-89 dosimetric models and absorbed doses were estimated using OLINDA/EXM V1.0 and OLINDA/EXM V2.0 (which use weighting factors from ICRP-103 to do the calculations). Results: The [(18)]FNM was stable in human plasma and the diffusible free fraction was 53%. As with memantine, this tracer is poorly metabolized in vivo. Ex vivo distributions validated PET/CT data as well as demonstrating a decrease of radiotracer uptake in the brain due to anesthesia. Total effective dose was around 6.11 mu Sv/MBg and 4.65 mu Sv/MBq for female and male human dosimetric models, respectively. Conclusions: This study shows that the presented compound exhibits stability in plasma and plasma protein binding very similar to memantine. Its dosimetry shows that it is suitable for use in humans due to a low total effective dose compared to other PET radiotracers. (C) 2018 Elsevier Inc. All rights reserved.

This study’s aim was to develop our dosimetric methodology using a commercial workstation for the routine evaluation of the organs at risk during peptide receptor radionuclide therapy (PRRT) with 177Lu.

The quality assurance program in a Nuclear Medicine Department aims to minimize errors and artifacts that cover all aspects of clinical practice. The quality control can be seen such as one particular procedure used to meet measurements that can be followed along the time. The intrinsic flood-field uniformity is one of the quality control procedures to evaluate the response of a gamma camera to a spatially uniform flux of an incident gamma radiation over the field of view. The purpose of this study is to test our gamma cameras, recording the integral and differential uniformity figures of the intrinsic uniformity during the 2007 in order to establish how well the instruments were working. At the beginning we perform an evaluation of our acquisition protocol which implies the variation of the acquired counts, the energy window width and its placement. After that we analyze the recording data creating plots which are showing the performance of the systems. Using an energy window placed at 140 keV at 20%, with matrix size of 512 x 512, acquiring 15 million counts and the source activity close to 700 °C; we think that we get a good enough images and both uniformities are within the manufacture's requirements, however, increasing the number of acquired counts, images are much better and an improvement in the evaluated parameters can be seen. The performance evaluation, of the three gamma cameras, was taking into account for approximately 240 days, showing an integral uniformity range of 1.04 ± 3.5 % and the range for differential uniformity vary from 0.88 up to 2.7 %. We conclude that the gamma cameras were working quite well, we do not need to vary our acquisition protocol because it is good enough to perform this test; also factors affecting the quality of the images are radioactive waste material not very well shielded and temperature room variations, especially at the beginning of our workday.

aInstitute of Nuclear Medicine, UCL, UK bQueen Elizabeth Hospital, Adelaide, Australia Abstracts of the 34th Annual Meeting of the British Nuclear Medicine Society Manchester International Conference Centre, UK, 27–29 March 2006