Deep transformer-based personalized dosimetry from SPECT/CT images: a hybrid approach for [177Lu]Lu-DOTATATE radiopharmaceutical therapy.

PURPOSE: Accurate dosimetry is critical for ensuring the safety and efficacy of radiopharmaceutical therapies. In current clinical dosimetry practice, MIRD formalisms are widely employed. However, with the rapid advancement of deep learning (DL) algorithms, there has been an increasing interest in leveraging the calculation speed and automation capabilities for different tasks. We aimed to develop a hybrid transformer-based deep learning (DL) model that incorporates a multiple voxel S-value (MSV) approach for voxel-level dosimetry in [177Lu]Lu-DOTATATE therapy. The goal was to enhance the performance of the model to achieve accuracy levels closely aligned with Monte Carlo (MC) simulations, considered as the standard of reference. We extended our analysis to include MIRD formalisms (SSV and MSV), thereby conducting a comprehensive dosimetry study. METHODS: We used a dataset consisting of 22 patients undergoing up to 4 cycles of [177Lu]Lu-DOTATATE therapy. MC simulations were used to generate reference absorbed dose maps. In addition, MIRD formalism approaches, namely, single S-value (SSV) and MSV techniques, were performed. A UNEt TRansformer (UNETR) DL architecture was trained using five-fold cross-validation to generate MC-based dose maps. Co-registered CT images were fed into the network as input, whereas the difference between MC and MSV (MC-MSV) was set as output. DL results are then integrated to MSV to revive the MC dose maps. Finally, the dose maps generated by MSV, SSV, and DL were quantitatively compared to the MC reference at both voxel level and organ level (organs at risk and lesions). RESULTS: The DL approach showed slightly better performance (voxel relative absolute error (RAE) = 5.28 ± 1.32) compared to MSV (voxel RAE = 5.54 ± 1.4) and outperformed SSV (voxel RAE = 7.8 ± 3.02). Gamma analysis pass rates were 99.0 ± 1.2%, 98.8 ± 1.3%, and 98.7 ± 1.52% for DL, MSV, and SSV approaches, respectively. The computational time for MC was the highest (~2 days for a single-bed SPECT study) compared to MSV, SSV, and DL, whereas the DL-based approach outperformed the other approaches in terms of time efficiency (3 s for a single-bed SPECT). Organ-wise analysis showed absolute percent errors of 1.44 ± 3.05%, 1.18 ± 2.65%, and 1.15 ± 2.5% for SSV, MSV, and DL approaches, respectively, in lesion-absorbed doses. CONCLUSION: A hybrid transformer-based deep learning model was developed for fast and accurate dose map generation, outperforming the MIRD approaches, specifically in heterogenous regions. The model achieved accuracy close to MC gold standard and has potential for clinical implementation for use on large-scale datasets.

Optimisation of protection in the medical exposure of recurrent adult patients due to computed tomography procedures: development of recurrent exposures reference levels.

OBJECTIVES: To assess the incidence (1 year) and the cumulative incidence (3 years) of the condition of patients accruing cumulative effective doses (CED) of ≥ 100 mSv and their variability among different hospitals. To establish and validate a reference level for the CED in patients with recurrent exposures (RERL) and provide a RERL value. METHODS: Data of CT exposure was collected in 9 similar hospitals. The database included 294,222 patient*years who underwent 442,278 CT exams in 3 years. The incidence proportion of patients with CED ≥ 100 mSv in a given year (I100;1) and the 3-year cumulative incidence of patients with CED ≥ 100 mSv over 3 consecutive years (I100;3) were calculated and compared among different institutions. RESULTS: I100;1 ranged from a minimum of 0.1% to a maximum of 5.1%. The percentage of recurrent patients was quite uniform among centres ranging from 23 to 38%. The I100;3 ranged from a minimum of 1.1 to 11.4%. There was a strong positive correlation between the third quartile values of yearly CED and yearly incidence (r = 0.90; R2 = 0.81; p < 0.0001). RERL value in our study was found at 34.0 mSv. CONCLUSION: The management of patients with recurrent exposures is highly variable among hospitals leading to a 50-fold variation in I100;1 and to a tenfold variation in I100;3. RERL could be established and used by taking as a RERL quantity the CED and as a RERL value the 75th percentile of the third quartiles of the distribution of the yearly CED obtained by surveying different hospitals. CLINICAL RELEVANCE STATEMENT: This is the first ever multicentre study that quantifies recurrent exposures in terms of incidence and cumulative incidence of patients with CED ≥ 100 mSv. RERL establishment and use could benefit the optimisation of radioprotection of patients with recurrent exposures. KEY POINTS: This is the first multicentre study estimating yearly incidence and 3-year cumulative incidence of patients with cumulative effective doses ≥ 100 mSv. In this study, a 50-fold inter centre variation between the maximum (5.1%) and the minimum value (0.1%) of yearly incidence of patients with cumulative effective doses ≥ 100 mSv was reported. The range of the 3-year cumulative incidence extended from 1.1 to 11.4% (a tenfold variation) The third quartile of the yearly cumulative effective doses in a centre showed a strong positive correlation with the yearly incidence of patients with cumulative effective doses ≥ 100 mSv, with a potential of being used to set reference levels for recurrent exposures.

Phase I, first-in-human study of XTR004, a novel 18F-labeled tracer for myocardial perfusion PET: Biodistribution, radiation dosimetry, pharmacokinetics, and safety after a single injection at rest.

OBJECTIVES: This study assessed the imaging characteristics, pharmacokinetics and safety of XTR004, a novel 18F-labeled Positron Emission Tomography (PET) myocardial perfusion imaging tracer, after a single injection at rest in humans. METHODS: Eleven healthy subjects (eight men and three women) received intravenous XTR004 (239-290 megabecquerel [MBq]). Safety profiles were monitored on the dosing day and three follow-up visits. Multiple whole-body PET scans were conducted over 4.7 h to evaluate biodistribution and radiation dosimetry. Blood and urine samples collected for 7.25 h were metabolically corrected to characterize pharmacokinetics. RESULTS: In the first 0-12 min PET images of ten subjects, liver (26.81 ± 4.01), kidney (11.43 ± 2.49), lung (6.75 ± 1.76), myocardium (4.72 ± 0.67) and spleen (3.1 ± 0.84) exhibited the highest percentage of the injected dose (%ID). Myocardial uptake of XTR004 in the myocardium initially reached 4.72 %ID and 7.06 g/mL, and negligibly changed within an hour (Δ: 7.20%, 5.95%). The metabolically corrected plasma peaked at 2.5 min (0.0013896 %ID/g) and halved at 45.2 min. Whole-body effective dose was 0.0165 millisievert (mSv)/MBq. Cumulative urine excretion was 8.18%. Treatment-related adverse events occurred in seven out of eleven subjects (63.6%), but no severe adverse event was reported. CONCLUSIONS: XTR004 demonstrated a favorable safety profile, rapid, high, and stable myocardial uptake and excellent potential for PET myocardial perfusion imaging (MPI). Further exploration of XTR004 PET MPI for detecting myocardial ischemia is warranted.

Development and validation of the low-cost pregnant female physical phantom for fetal dosimetry in MV photon radiotherapy.

BACKGROUND: Monte Carlo (MC) simulations or measurements in anthropomorphic phantoms are recommended for estimating fetal dose in pregnant patients in radiotherapy. Among the many existing phantoms, there is no commercially available physical phantom representing the entire pregnant woman. PURPOSE: In this study, the development of a low-cost, physical pregnant female phantom was demonstrated using commercially available materials. This phantom is based on the previously published computational phantom. METHODS: Three tissue substitution materials (soft tissue, lung and bone tissue substitution) were developed. To verify Tena's substitution tissue materials, their radiation properties were assessed and compared to ICRP and ICRU materials using MC simulations in MV radiotherapy beams. Validation of the physical phantom was performed by comparing fetal doses obtained by measurements in the phantom with fetal doses obtained by MC simulations in computational phantom, during an MV photon breast radiotherapy treatment. RESULTS: Materials used for building Tena phantom are matched to ICRU materials using physical density, radiation absorption properties and effective atomic number. MC simulations showed that percentage depth doses of Tena and ICRU material comply within 5% for soft and lung tissue, up to 25 cm depth. In the bone tissue, the discrepancy is higher, but again within 5% up to the depth of 5 cm. When the phantom was used for fetal dose measurements in MV photon breast radiotherapy, measured fetal doses complied with fetal doses calculated using MC simulation within 15%. CONCLUSIONS: Physical anthropomorphic phantom of pregnant patient can be manufactured using commercial materials and with low expenses. The files needed for 3D printing are now freely available. This enables further studies and comparison of numerical and physical experiments in diagnostic radiology or radiotherapy.

Radioactive seed localization is a safe and effective tool for breast cancer surgery: an evaluation of over 25,000 cases.

Radioactive seed localization (RSL) provides a precise and efficient method for removing non-palpable breast lesions. It has proven to be a valuable addition to breast surgery, improving perioperative logistics and patient satisfaction. This retrospective review examines the lessons learned from a high-volume cancer center's RSL program after 10 years of practice and over 25 000 cases. We provide an updated model for assessing the patient's radiation dose from RSL seed implantation and demonstrate the safety of RSL to staff members. Additionally, we emphasize the importance of various aspects of presurgical evaluation, surgical techniques, post-surgical management, and regulatory compliance for a successful RSL program. Notably, the program has reduced radiation exposure for patients and medical staff.

Radiation exposure in augmented fluoroscopic bronchoscopy procedures: a comprehensive analysis for patients and physicians.

Cancer is a major health challenge and causes millions of deaths worldwide each year, and the incidence of lung cancer has increased. Augmented fluoroscopic bronchoscopy (AFB) procedures, which combine bronchoscopy and fluoroscopy, are crucial for diagnosing and treating lung cancer. However, fluoroscopy exposes patients and physicians to radiation, and therefore, the procedure requires careful monitoring. The National Council on Radiation Protection and Measurement and the International Commission on Radiological Protection have emphasised the importance of monitoring patient doses and ensuring occupational radiation safety. The present study evaluated radiation doses during AFB procedures, focusing on patient skin doses, the effective dose, and the personal dose equivalent to the eye lens for physicians. Skin doses were measured using thermoluminescent dosimeters. Peak skin doses were observed on the sides of the patients' arms, particularly on the side closest to the x-ray tube. Differences in the procedures and experience of physicians between the two hospitals involved in this study were investigated. AFB procedures were conducted more efficiently at Hospital A than at Hospital B, resulting in lower effective doses. Cone-beam computed tomography (CT) contributes significantly to patient effective doses because it has higher radiographic parameters. Despite their higher radiographic parameters, AFB procedures resulted in smaller skin doses than did image-guided interventional and CT fluoroscopy procedures. The effective doses differed between the two hospitals of this study due to workflow differences, with cone-beam CT playing a dominant role. No significant differences in left and right eyeHp(3) values were observed between the hospitals. For both hospitals, theHp(3) values were below the recommended limits, indicating that radiation monitoring may not be required for AFB procedures. This study provides insights into radiation exposure during AFB procedures, concerning radiation dosimetry, and safety for patients and physicians.

Longitudinal multi-omic changes in the transcriptome and proteome of peripheral blood cells after a 4 Gy total body radiation dose to Rhesus macaques.

BACKGROUND: Non-human primates, such as Rhesus macaques, are a powerful model for studies of the cellular and physiological effects of radiation, development of radiation biodosimetry, and for understanding the impact of radiation on human health. Here, we study the effects of 4 Gy total body irradiation (TBI) at the molecular level out to 28 days and at the cytogenetic level out to 56 days after exposure. We combine the global transcriptomic and proteomic responses in peripheral whole blood to assess the impact of acute TBI exposure at extended times post irradiation. RESULTS: The overall mRNA response in the first week reflects a strong inflammatory reaction, infection response with neutrophil and platelet activation. At 1 week, cell cycle arrest and re-entry processes were enriched among mRNA changes, oncogene-induced senescence and MAPK signaling among the proteome changes. Influenza life cycle and infection pathways initiated earlier in mRNA and are reflected among the proteomic changes during the first week. Transcription factor proteins SRC, TGFß and NFATC2 were immediately induced at 1 day after irradiation with increased transcriptional activity as predicted by mRNA changes persisting up to 1 week. Cell counts revealed a mild / moderate hematopoietic acute radiation syndrome (H-ARS) reaction to irradiation with expected lymphopenia, neutropenia and thrombocytopenia that resolved within 30 days. Measurements of micronuclei per binucleated cell levels in cytokinesis-blocked T-lymphocytes remained high in the range 0.27-0.33 up to 28 days and declined to 0.1 by day 56. CONCLUSIONS: Overall, we show that the TBI 4 Gy dose in NHPs induces many cellular changes that persist up to 1 month after exposure, consistent with damage, death, and repopulation of blood cells.

Human biodistribution and radiation dosimetry of the demyelination tracer [18F]3F4AP.

PURPOSE: [18F]3F4AP is a novel PET radiotracer that targets voltage-gated potassium (K+) channels and has shown promise for imaging demyelinated lesions in animal models of neurological diseases. This study aimed to evaluate the biodistribution, safety, and radiation dosimetry of [18F]3F4AP in healthy human volunteers. METHODS: Four healthy volunteers (2 females) underwent a 4-h dynamic PET scan from the cranial vertex to mid-thigh using multiple bed positions after administration of 368 ± 17.9 MBq (9.94 ± 0.48 mCi) of [18F]3F4AP. Volumes of interest for relevant organs were manually drawn guided by the CT, and PET images and time-activity curves (TACs) were extracted. Radiation dosimetry was estimated from the integrated TACs using OLINDA software. Safety assessments included measuring vital signs immediately before and after the scan, monitoring for adverse events, and obtaining a comprehensive metabolic panel and electrocardiogram within 30 days before and after the scan. RESULTS: [18F]3F4AP distributed throughout the body with the highest levels of activity in the kidneys, urinary bladder, stomach, liver, spleen, and brain and with low accumulation in muscle and fat. The tracer cleared quickly from circulation and from most organs. The clearance of the tracer was noticeably faster than previously reported in nonhuman primates (NHPs). The average effective dose (ED) across all subjects was 12.1 ± 2.2 µSv/MBq, which is lower than the estimated ED from the NHP studies (21.6 ± 0.6 µSv/MBq) as well as the ED of other fluorine-18 radiotracers such as [18F]FDG (~ 20 µSv/MBq). No differences in ED between males and females were observed. No substantial changes in safety assessments or adverse events were recorded. CONCLUSION: The biodistribution and radiation dosimetry of [18F]3F4AP in humans are reported for the first time. The average total ED across four subjects was lower than most 18F-labeled PET tracers. The tracer and study procedures were well tolerated, and no adverse events occurred.

Preclinical Evaluation of a Companion Diagnostic Radiopharmaceutical, [18F]PSMA-1007, in a Subcutaneous Prostate Cancer Xenograft Mouse Model.

Several radiolabeled prostate-specific membrane antigen (PSMA)-targeted agents have been developed for detecting prostate cancer, using positron emission tomography imaging and targeted radionuclide therapy. Among them, [18F]PSMA-1007 has several advantages, including a comparatively long half-life, delayed renal excretion, and compatible structure with α-/ß-particle emitter-labeled therapeutics. This study aimed to characterize the preclinical pharmacokinetics and internal radiation dosimetry of [18F]PSMA-1007, as well as its repeatability and specificity for target binding using prostate tumor-bearing mice. In PSMA-positive tumor-bearing mice, the kidney showed the greatest accumulation of [18F]PSMA-1007. The distribution in the tumor attained its peak concentration of 2.8%ID/g at 112 min after intravenous injection. The absorbed doses in the tumor and salivary glands were 0.079 ± 0.010 Gy/MBq and 0.036 ± 0.006 Gy/MBq, respectively. The variance of the net influx (Ki) of [18F]PSMA-1007 to the tumor was minimal between scans performed in the same animals (within-subject coefficient of variation = 7.57%). [18F]PSMA-1007 uptake in the tumor was specifically decreased by 32% in Ki after treatment with a PSMA inhibitor 2-(phosphonomethyl)-pentanedioic acid (2-PMPA). In the present study, we investigated the in vivo preclinical characteristics of [18F]PSMA-1007. Our data from [18F]PSMA-1007 PET/computed tomography (CT) studies in a subcutaneous prostate cancer xenograft mouse model supports clinical therapeutic strategies that use paired therapeutic radiopharmaceuticals (such as [177Lu]Lu-PSMA-617), especially strategies with a quantitative radiation dose estimate for target lesions while minimizing radiation-induced toxicity to off-target tissues.

Theranostic Surrogacy of [123I]NaI for Differentiated Thyroid Cancer Radionuclide Therapy.

Precise dosimetry has gained interest for interpreting the response assessments of novel therapeutic radiopharmaceuticals, as well as for improving conventional radiotherapies such as the "one dose fits all" approach. Although radioiodine as same-element isotope theranostic pairs has been used for differentiated thyroid cancer (DTC), there are insufficient studies on the determination of its dosing regimen for personalized medicine and on extrapolating strategies for companion diagnostic radiopharmaceuticals. In this study, DTC xenograft mouse models were generated after validating iodine uptakes via sodium iodine symporter proteins (NIS) through in vitro assays, and theranostic surrogacy of companion radiopharmaceuticals was investigated in terms of single photon emission computed tomography (SPECT) imaging and voxel-level dosimetry. Following a Monte Carlo simulation, the hypothetical energy deposition/dose distribution images were produced as [123I]NaI SPECT scans with the use of 131I ion source simulation, and dose rate curves were used to estimate absorbed dose. For the tumor, a peak concentration of 96.49 ± 11.66% ID/g occurred 2.91 ± 0.42 h after [123I]NaI injection, and absorbed dose for 131I therapy was estimated as 0.0344 ± 0.0088 Gy/MBq. The absorbed dose in target/off-target tissues was estimated by considering subject-specific heterogeneous tissue compositions and activity distributions. Furthermore, a novel approach was proposed for simplifying voxel-level dosimetry and suggested for determining the minimal/optimal scan time points of surrogates for pretherapeutic dosimetry. When two scan time points were set to Tmax and 26 h and the group mean half-lives were applied to the dose rate curves, the most accurate absorbed dose estimates were determined [-22.96, 2.21%]. This study provided an experimental basis to evaluate dose distribution and is expected hopefully to improve the challenging dosimetry process for clinical use.

Optimized radiological alert thresholds based on device-dosimetric information to predict peak skin dose between 2 and 4 Gy during vascular fluoroscopically guided intervention.

OBJECTIVES: To provide radiologists and physicists with methodological tools to improve patient management after vascular fluoroscopically guided intervention (FGI) by providing optimized thresholds (OT) values that could be used as a surrogate to the thresholds classically proposed by the National Council on Radiation Protection (NCRP) or could be useful to adapt their own substantial radiation dose levels (SRDL) values. METHODS: PSD of 2000-4000 mGy after FGI were calculated for 258 patients with dedicated software. Overall, the kerma and KAP 3D-ROC curves were used to assess the sensitivity (SEN) and specificity (SPE) of NCRP thresholds and OT for each PSD. Kiviat diagram and density curves were plotted for the best SEN/SPE pair of 3D-ROC curves and compared to the NCRP thresholds. RESULTS: OT for both kerma and KAP generating the best SEN/SPE couple for PSD of 2000-4000 mGy were obtained. The SEN/SPE couple of each OT was always better than that obtained using NCRP ones. The best OT among all those calculated providing the highest SEN/SPE values for kerma (3020.5 mGy) and KAP (741.02 Gy.cm2) were obtained when PSD was equal to 3300 mGy. CONCLUSIONS: We have calculated OT in terms of kerma and KAP based on 3D-ROC curves analysis and peak skin dose calculations that can be obtained to better predict high skin dose. The use of OT that predicted PSD greater than 3000 mGy is likely to improve patient follow-up. The methodology developed in this work could be adapted to other institutions in order to better define their own SRDL. KEY POINTS: • Optimized dose thresholds in terms of kerma and KAP based on 3D-ROC curves analysis and peak skin dose calculations between 2000 and 4000 mGy can be obtained to better predict high skin dose. • Patients receiving a peak skin dose between 2000 and 4000 mGy have their follow-up enhanced by using the optimized thresholds instead of the NCRP thresholds. • The best-optimized thresholds, corresponding to 3020.5 mGy and 741.02 Gy.cm2 for kerma and KAP respectively can be used instead of NRCP ones to trigger patient follow-up after fluoroscopically guided vascular interventions.

Fetal atomic bomb survivor dosimetry using the J45 series of pregnant female phantoms with realistic survivor exposure scenarios: comparisons to dose estimates in the DS02 system.

A significant source of information on radiation-induced biological effects following in-utero irradiation stems from studies of atomic bomb survivors who were pregnant at the time of exposure in Hiroshima, and to a lesser extent, from survivors in Nagasaki. Dose estimates to the developing fetus for these survivors have been assigned in prior dosimetry systems of the Radiation Effects Research Foundation as the dose to the uterine wall within the non-pregnant adult stylized phantom, originally designed for the dosimetry system DS86 and then carried forward in DS02. In a prior study, a new J45 (Japanese 1945) series of high-resolution phantoms of the adult pregnant female at 8 weeks, 15 weeks, 25 weeks, and 38-weeks post-conception was presented. Fetal and maternal organ doses were estimated by computationally exposing the pregnant female phantom series to DS02 free-in-air cumulative photon and neutron fluences at three distances from the hypocenter at both Hiroshima and Nagasaki under idealized frontal (AP) and isotropic (ISO) particle incidence. In this present study, this work was extended using realistic angular fluences (480 directions) from the DS02 system for seven radiation source terms, nine different radiation dose components, and five shielding conditions. In addition, to explore the effects of fetal position within the womb, four new phantoms were created and the same irradiation scenarios were performed. General findings are that the current DS02 fetal dose surrogate overestimates values of fetal organ dose seen in the J45 phantoms towards the cranial end of the fetus, especially in the later stages of pregnancy. For example, for in-open exposures at 1000 m in Hiroshima, the ratio of J45 fetal brain dose to DS02 uterine wall dose is 0.90, 0.82, and 0.70 at 15 weeks, 25 weeks, and 38-weeks, respectively, for total gamma exposures, and are 0.64, 0.44, and 0.37 at these same gestational ages for total neutron exposures. For organs in the abdominal and pelvic regions of the fetus, dose gradients across gestational age flatten and later reverse, so that DS02 fetal dosimetry begins to underestimate values of fetal organ dose as seen in the J45 phantoms. For example, for the same exposure scenario, the ratios of J45 fetal kidney dose to DS02 uterine wall dose are about 1.09 from 15 to 38 weeks for total gamma dose, and are 1.30, 1.56, and 1.75 at 15 weeks, 25 weeks, and 38 weeks, respectively, for the total neutron dose. Results using the new fetal positioning phantoms show this trend reversing for a head-up, breach fetal position. This work supports previous findings that the J45 pregnant female phantom series offers significant opportunities for gestational age-dependent assessment of fetal organ dose without the need to invoke the uterine wall as a fetal organ surrogate.

Reduction of radiation dose using real-time visual feedback dosimetry during angiographic interventions.

This prospective study sought to evaluate potential savings of radiation dose to medical staff using real-time dosimetry coupled with visual radiation dose feedback during angiographic interventions. For this purpose, we analyzed a total of 214 angiographic examinations that consisted of chemoembolizations and several other types of therapeutic interventions. The Unfors RaySafe i2 dosimeter was worn by the interventionalist at chest height over the lead protection. A total of 110 interventions were performed with real-time radiation dosimetry allowing the interventionalist to react upon higher x-ray exposure and 104 examinations served as the comparative group without real-time radiation monitoring. By using the real-time display during interventions, the overall mean operator radiation dose decreased from 3.67 (IQR, 0.95-23.01) to 2.36 µSv (IQR, 0.52-12.66) (-36%; p = 0.032) at simultaneously reduced operator exposure time by 4.5 min (p = 0.071). Dividing interventions into chemoembolizations and other types of therapeutic interventions, radiation dose decreased from 1.31 (IQR, 0.46-3.62) to 0.95 µSv (IQR, 0.53-3.11) and from 24.39 (IQR, 12.14-63.0) to 10.37 µSv (IQR, 0.85-36.84), respectively, using live-screen dosimetry (p ≤ 0.005). Radiation dose reductions were also observed for the participating assistants, indicating that they could also benefit from real-time visual feedback dosimetry during interventions (-30%; p = 0.039). Integration of real-time dosimetry into clinical processes might be useful in reducing occupational radiation exposure time during angiographic interventions. The real-time visual feedback raised the awareness of interventionalists and their assistants to the potential danger of prolonged radiation exposure leading to the adoption of radiation-sparing practices. Therefore, it might create a safer environment for the medical staff by keeping the applied radiation exposure as low as possible.

Use of Thermoluminescence Dosimetry for QA in High-Dose-Rate Skin Surface Brachytherapy with Custom-Flap Applicator.

Surface brachytherapy (BT) lacks standard quality assurance (QA) protocols. Commercially available treatment planning systems (TPSs) are based on a dose calculation formalism that assumes the patient is made of water, resulting in potential deviations between planned and delivered doses. Here, a method for treatment plan verification for skin surface BT is reported. Chips of thermoluminescent dosimeters (TLDs) were used for dose point measurements. High-dose-rate treatments were simulated and delivered through a custom-flap applicator provided with four fixed catheters to guide the Iridium-192 (Ir-192) source by way of a remote afterloading system. A flat water-equivalent phantom was used to simulate patient skin. Elekta TPS Oncentra Brachy was used for planning. TLDs were calibrated to Ir-192 through an indirect method of linear interpolation between calibration factors (CFs) measured for 250 kV X-rays, Cesium-137, and Cobalt-60. Subsequently, plans were designed and delivered to test the reproducibility of the irradiation set-up and to make comparisons between planned and delivered dose. The obtained CF for Ir-192 was (4.96 ± 0.25) µC/Gy. Deviations between measured and TPS calculated doses for multi-catheter treatment configuration ranged from -8.4% to 13.3% with an average of 0.6%. TLDs could be included in clinical practice for QA in skin BT with a customized flap applicator.

Cardiologist's exposure to radiation in cath lab measured with InstadoseTMdosimeter.

INTRODUCTION: complex fluoroscopy-guided interventional procedures in cardiology are known to result in higher radiation doses for patients and staff. PURPOSE: to estimate the equivalent dose received in different regions of the cardiologist's body in catheterism (CATH) and percutaneous coronary intervention (PCI) procedures, as well as to evaluate the effectiveness of monitoring the doses in the catheritization laboratory (cath lab) using a direct ion storage dosimeter. MATERIALS AND METHODS: the InstadoseTMand the thermoluminescent dosimeters (TLD-100) were fixed simultaneously in the following regions of the cardiologist's body: near the eyes (left and right), the trunk region (over the lead apron) and the left ankle. Occupational doses were recorded during 86 procedures (60% CATH). RESULTS: catheterization procedures showed third quartile dose values near to the left eye region equal to 0.10 mSv (TLD-100) and 0.12 (InstadoseTM) and for intervention 0.15 mSv (TLD-100 and InstadoseTM). The doses measured in the trunk region, over the lead apron, were about 13% higher for catheterization procedures and 20% higher for intervention procedures compared to left eye region measurements. The Wilcoxon-Mann-Whitney test was applied for unpaired data for all body regions, comparing the data obtained between the TLD-100 and InstadoseTMdosimeters. For CATH and PCI, the responses of the TLD-100 and InstadoseTMdosimeters are considered equal for all analysed regions (p> 0.05) with the exception of the right eye region. CONCLUSION: the InstadoseTMpassive dosimeter can be useful as a complementary assessment in the monitoring of a cardiologist's personal occupational doses in the cath lab.

Absorbed dose coefficients for adult thyroid cancer patients undergoing radioiodine therapy.

Use of radioactive iodine (RAI) for thyroid cancer patients is accompanied by elevated risks of radiation-induced adverse effects due to significant radiation exposure of normal tissues or organs other than the thyroid. The health risk estimation for thyroid cancer patients should thus be preceded by estimating normal tissue doses. Although organ dose estimation for a large cohort often relies on absorbed dose coefficients (i.e. absorbed dose per unit activity administered, mGy MBq-1) based on population models, no data are available for thyroid cancer patients. In the current study, we calculated absorbed dose coefficients specific for adult thyroid cancer patients undergoing RAI treatment after recombinant human TSH (rhTSH) administration or thyroid hormone withdrawal (THW). We first adjusted the transfer rates in the biokinetic model previously developed for THW patients for use in rhTSH patients. We then implemented the biokinetic models for thyroid cancer patients coupled withSvalues from the International Commission on Radiological Protection (ICRP) reference voxel phantoms to calculate absorbed dose coefficients. The biokinetic model for rhTSH patients predicted the extrathyroidal iodine decreasing noticeably faster than in the model for THW patients (calculated half-times of 12 and 15 h for rhTSH administration and THW, respectively). All dose coefficients for rhTSH patients were lower than those for THW patients with the ratio (rhTSH administration/THW) ranging from 0.60 to 0.95 (mean = 0.67). The ratio of the absorbed dose coefficients in the current study to the ICRP dose coefficients, which were derived from models for normal subjects, varied widely from 0.21 to 7.19, stressing the importance of using the dose coefficients for thyroid cancer patients. The results of this study will provide medical physicists and dosimetrists with scientific evidence to protect patients from excess exposure or to assess radiation-induced health risks caused by RAI treatment.

A New Method of Matrix-Based Triage for Nuclear Disasters.

During nuclear disaster, infrastructure is severely damaged and injuries are often combined with trauma/burns and whole-body radiation. This makes triage difficult, especially when resources are severely deficient. To solve this problem, in this article, the authors have suggested a new less technology-dependent radiation dosimetry and quick triage using a specially designed triage matrix during nuclear disasters.

A novel methodology to train and deploy a machine learning model for personalized dose assessment in head CT.

OBJECTIVES: To propose a machine learning-based methodology for the creation of radiation dose maps and the prediction of patient-specific organ/tissue doses associated with head CT examinations. METHODS: CT data were collected retrospectively for 343 patients who underwent standard head CT examinations. Patient-specific Monte Carlo (MC) simulations were performed to determine the radiation dose distribution to patients' organs/tissues. The collected CT images and the MC-produced dose maps were processed and used for the training of the deep neural network (DNN) model. For the training and validation processes, data from 231 and 112 head CT examinations, respectively, were used. Furthermore, a software tool was developed to produce dose maps from head CT images using the trained DNN model and to automatically calculate the dose to the brain and cranial bones. RESULTS: The mean (range) percentage differences between the doses predicted from the DNN model and those provided by MC simulations for the brain, eye lenses, and cranial bones were 4.5% (0-17.7%), 5.7% (0.2-19.0%), and 5.2% (0.1-18.9%), respectively. The graphical user interface of the software offers a user-friendly way for radiation dose/risk assessment. The implementation of the DNN allowed for a 97% reduction in the computational time needed for the dose estimations. CONCLUSIONS: A novel methodology that allows users to develop a DNN model for patient-specific CT dose prediction was developed and implemented. The approach demonstrated herein allows accurate and fast radiation dose estimation for the brain, eye lenses, and cranial bones of patients who undergo head CT examinations and can be used in everyday clinical practice. KEY POINTS: • The methodology presented herein allows fast and accurate radiation dose estimation for the brain, eye lenses, and cranial bones of patients who undergo head CT examinations and can be implemented in everyday clinical practice. • The scripts developed in the current study will allow users to train models for the acquisition protocols of their CT scanners, generate dose maps, estimate the doses to the brain and cranial bones, and estimate the lifetime attributable risk of radiation-induced brain cancer.

Radiation exposure and establishment of diagnostic reference levels of whole-body low-dose CT for the assessment of multiple myeloma with second- and third-generation dual-source CT.

BACKGROUND: In the assessment of diseases causing skeletal lesions such as multiple myeloma (MM), whole-body low-dose computed tomography (WBLDCT) is a sensitive diagnostic imaging modality, which has the potential to replace the conventional radiographic survey. PURPOSE: To optimize radiation protection and examine radiation exposure, and effective and organ doses of WBLDCT using different modern dual-source CT (DSCT) devices, and to establish local diagnostic reference levels (DRL). MATERIAL AND METHODS: In this retrospective study, 281 WBLDCT scans of 232 patients performed between January 2017 and April 2020 either on a second- (A) or third-generation (B) DSCT device could be included. Radiation exposure indices and organ and effective doses were calculated using a commercially available automated dose-tracking software based on Monte-Carlo simulation techniques. RESULTS: The radiation exposure indices and effective doses were distributed as follows (median, interquartile range): (A) second-generation DSCT: volume-weighted CT dose index (CTDIvol) 1.78 mGy (1.47-2.17 mGy); dose length product (DLP) 282.8 mGy·cm (224.6-319.4 mGy·cm), effective dose (ED) 1.87 mSv (1.61-2.17 mSv) and (B) third-generation DSCT: CTDIvol 0.56 mGy (0.47-0.67 mGy), DLP 92.0 mGy·cm (73.7-107.6 mGy·cm), ED 0.61 mSv (0.52-0.69 mSv). Radiation exposure indices and effective and organ doses were significantly lower with third-generation DSCT (P < 0.001). Local DRLs could be set for CTDIvol at 0.75 mGy and DLP at 120 mGy·cm. CONCLUSION: Third-generation DSCT requires significantly lower radiation dose for WBLDCT than second-generation DSCT and has an effective dose below reported doses for radiographic skeletal surveys. To ensure radiation protection, DRLs regarding WBLDCT are required, where our locally determined values may help as benchmarks.

Out-of-field effects: lessons learned from partial body exposure.

Partial body exposure and inhomogeneous dose delivery are features of the majority of medical and occupational exposure situations. However, mounting evidence indicates that the effects of partial body exposure are not limited to the irradiated area but also have systemic effects that are propagated outside the irradiated field. It was the aim of the "Partial body exposure" session within the MELODI workshop 2020 to discuss recent developments and insights into this field by covering clinical, epidemiological, dosimetric as well as mechanistic aspects. Especially the impact of out-of-field effects on dysfunctions of immune cells, cardiovascular diseases and effects on the brain were debated. The presentations at the workshop acknowledged the relevance of out-of-field effects as components of the cellular and organismal radiation response. Furthermore, their importance for the understanding of radiation-induced pathologies, for the discovery of early disease biomarkers and for the identification of high-risk organs after inhomogeneous exposure was emphasized. With the rapid advancement of clinical treatment modalities, including new dose rates and distributions a better understanding of individual health risk is urgently needed. To achieve this, a deeper mechanistic understanding of out-of-field effects in close connection to improved modelling was suggested as priorities for future research. This will support the amelioration of risk models and the personalization of risk assessments for cancer and non-cancer effects after partial body irradiation.