Whole-body Dose Research Articles

Efficacy and Safety of 124I-MIBG Dosimetry-Guided High-Activity 131I-MIBG Therapy of Advanced Pheochromocytoma or Neuroblastoma.

We aim to evaluate the efficacy and safety of 124I-metaiodobenzylguanidine (MIBG) dosimetry-guided high-activity 131I-MIBG therapy of advanced pheochromocytoma or neuroblastoma. Methods: Fourteen patients with advanced pheochromocytoma or neuroblastoma, age 9-69 y, underwent 124I-MIBG PET scans and whole-body retention measurements to assess the whole-body dose as a surrogate of bone marrow toxicity and tumor (absorbed) dose per unit of administered activity. Dosimetry results together with individual patient characteristics were combined to guide a single therapeutic activity to achieve a high tumor dose without exceeding toxicity threshold. Toxicity was assessed for hematologic, hepatic, and renal function. Response was evaluated by RECIST, International Society of Pediatric Oncology Europe Neuroblastoma-like score, change in PET uptake, and quantitative PET parameters (SUVmax, SUVpeak, metabolic tumor volume, total lesion glycolysis), as well as visual decrease in number or in visual intensity of lesions on baseline to follow-up 124I-MIBG PET/CT. Results: The average therapeutic activity was 14 GBq. Eleven of 14 patients (79%) received each more than 10 GBq. One male patient was treated with a single activity of 50 GBq. Three patients were treated with lower activities between 3.5 and 7.0 GBq. Median overall survival was 85 mo (95% CI), and median progression-free survival was 25 mo (95% CI). Four (29%) and 5 (36%) patients demonstrated response (complete response or partial response) by RECIST and functional imaging, respectively. One patient exceeded whole-body dose of 2 Gy and demonstrated grade 3 hematologic toxicity, which resolved spontaneously within 12 mo after the therapy without the need for further treatment. Three patients (21%) demonstrated transient grade 1 renal toxicity. Conclusion: 124I-MIBG dosimetry-guided high-activity 131I-MIBG therapy in patients with advanced pheochromocytoma or neuroblastoma resulted in durable responses with a low rate of manageable adverse events. Efficacy of 124I-MIBG-guided activity escalation should further be assessed in a prospective setting.

New perforated radiation shield for anesthesiologists: Monte Carlo simulation of effects.

Catheterization for structural heart disease (SHD) requires fluoroscopic guidance, which exposes health care professionals to radiation exposure risk. Nevertheless, existing freestanding radiation shields for anesthesiologists are typically simple, uncomfortable rectangles. Therefore, we devised a new perforated radiation shield that allows anesthesiologists and echocardiographers to access a patient through its apertures during SHD catheterization. No report of the relevant literature has described the degree to which the anesthesiologist's radiation dose can be reduced by installing radiation shields. For estimating whole-body doses to anesthesiologists and air dose distributions in the operating room, we used a Monte Carlo system for a rapid dose-estimation system used with interventional radiology. The simulations were performed under four conditions: no radiation shield, large apertures, small apertures and without apertures. With small apertures, the doses to the lens, waist and neck surfaces were found to be comparable to those of a protective plate without an aperture, indicating that our new radiation shield copes with radiation protection and work efficiency. To simulate the air-absorbed dose distribution, results indicated that a fan-shaped area of the dose rate decrease was generated in the area behind the shield, as seen from the tube sphere. For the aperture, radiation was found to wrap around the backside of the shield, even at a height that did not match the aperture height. The data presented herein are expected to be of interest to all anesthesiologists who might be involved in SHD catheterization. The data are also expected to enhance their understanding of radiation exposure protection.

Modelling of daily radiofrequency electromagnetic field dose for a prospective adolescent cohort

IntroductionRadiofrequency electromagnetic fields originate from a variety of wireless communication sources operating near and far from the body, making it challenging to quantify daily absorbed dose. In the framework of the prospective cohort SCAMP (Study of Cognition, Adolescents and Mobile Phones), we aimed to characterize RF-EMF dose over a 2-year period. MethodsThe SCAMP cohort included 6605 children from greater London, UK at baseline (age 12.1 years; 2014–2016) and 5194 at follow-up (age 14.2; 2016–2018). We estimated the daily dose of RF-EMF to eight tissues including the whole body and whole brain, using dosimetric algorithms for the specific absorption rate transfer into the body. We considered RF-EMF dose from 12 common usage scenarios such as mobile phone calls or data transmission. We evaluated the association between sociodemographic factors (gender, ethnicity, phone ownership and socio-economic status), and the dose change between baseline and follow-up. ResultsWhole body dose was estimated at an average of 170 mJ/kg/day at baseline and 178 mJ/kg/day at follow-up. Among the eight tissues considered, the right temporal lobe received the highest daily dose (baseline 1150 mJ/kg/day, follow-up 1520 mJ/kg/day). Estimated daily dose [mJ/kg/day] increased between baseline and follow-up for head and brain related tissues, but remained stable for the whole body and heart. Doses estimated at baseline and follow-up showed low correlation among the 3384 children who completed both assessments. Asian ethnicity (compared to white) and owning a bar phone or no phone (as opposed to a smartphone) were associated with lower estimated whole-body and whole-brain RF-EMF dose, while black ethnicity, a moderate/low socio-economic status (compared to high), and increasing age (at baseline) were associated with higher estimated RF-EMF dose. ConclusionThis study describes the first longitudinal exposure assessment for children in a critical period of development. Dose estimations will be used in further epidemiological analyses for the SCAMP study.

ASSESSMENT OF OCCUPATIONAL EXPOSURE TO EXTERNAL RADIATION AMONG WORKERS OF THREE COMMUNITY HOSPITALS IN SENEGAL.

Occupational radiation doses of 602 medical workers from the departments of Radiology, Thoracic and cardiovascular surgery, Operating room, Nuclear medicine, Radiotherapy and cardiology were evaluated during 2017 to 2021 in three hospitals in Senegal. Each hospital was subdivided into various occupational groups. Whole-body doses Hp(10), local skin doses Hp(0.07) and annual collective dose Hp(10) were measured by OSL (optically stimulated luminescence) dosimetry. The occupational groups with the highest radiation exposures, ~0.185mSv in 1y, were in the field of nuclear medicine, radiology, cardiology, Thoracic and cardiovascular surgery and Operating room. All results of the measured annual effective dose were below the ICRP (International Commission on Radiological Protection) dose limits of 20 mSv/y, averaged over any 5-y period.

Semi-mechanistic analysis of emergency planning zones for 20 MWe lead-cooled fast reactor by hypothetical accidents during Korea's arctic exploration

Small modular reactors or micro modular reactors have been considered as an alternative power source for merchant ships because of minimal carbon emission and a long lifecycle without refueling. Ahead of the operation, however, their emergency planning zones (EPZs) should be optimally set and approved to ensure both radiological safety and cost efficiency in case of nuclear accidents. Thus, the required size of EPZs was analyzed based on semi-mechanistic assumptions for hypothetical accidents with MicroURANUS, a micro modular fast reactor type of 20-MW lead-bismuth-cooled, used to power an icebreaker during Korea's Arctic missions. For meteorological data, actual icebreaker data acquired in 2020s Artic exploration were utilized. The results showed that EPZ sizes, rationalized in terms of stability class, wind directions, and inherent radioprotection design, ranged within the assumed icebreaker boundary. When comparing various regulations among countries and the International Atomic Energy Agency, dose criteria of Korea (10 mSv/2 d) were found to be strictest. Since major contribution to the whole-body dose was from noble gases (over 96%), a high-quality air filtration system in addition to external shielding would significantly reduce hazards. The emergency situation could be successfully controlled without evacuation and sheltering, avoiding overestimated socioeconomic costs.

ESTIMATION OF PATIENT ORGAN AND WHOLE-BODY DOSES IN [18F-FDG] PET/CT SCAN.

The object of this study was to estimate organ doses and whole-body effective doses from positron emission tomography/computed tomography (PET/CT) scan using [fluorine-18]-fluoro-2-deoxy-d-glucose (18F-FDG) in adult patients and to assess the CT component contribution to organ and whole-body doses. The [18F-FDG] PET/CT scan was conducted on 204 adult patients (90 females and 114 males). For all patients, females and males, the whole-body effective doses were 20.54, 23.89 and 17.89mSv, respectively. For all patients, females and males, the CT component contribution to the whole-body effective dose was 66, 71 and 62%, respectively. Since CT is the primary contributor to the effective dose in the [18F-FDG] PET/CT scan protocol, the significance of improving CT protocols to minimize patient dose is underscored. All attempts must be made, using available mechanisms and techniques, to reduce the patient's dose of PET/CT scan, especially in obese patients.

X-ray Target Shielding and Leakage Radiation Inside the Treatment Capsule of the Zap-X.

The ZAP-X represents the first-of-its-kind "self-shielded" therapeutic radiation device, which by novelty, challenges regulators to accommodate it within the existing regulatory framework for radiation protection. To facilitate informed regulatory interpretation, X-ray radiation leakage from the ZAP-X was measured inside the shielded treatment capsule at the level of the patient and X-ray target plane. Measurements were performed on a clinically commissioned system calibrated for reference conditions to deliver 1cGy/MU. Radiation was measured with a FLUKE 451 survey meter and a RadCal ionization chamber as both exposure and dose and presented as a percentage of the system reference dose. Measurements were taken at thirteen locations, eight in the patient plane and five in the X-ray target plane. The results showed a maximum X-ray leakage of 0.000986% in the patient plane and 0.000907% in the target plane. These results are 30 - 100 times lower than existing recommendations as referenced by IEC guidelines standard 60601-2-1 (2020) for radiotherapy linear accelerators (LINACs). Although most conventional LINACs apply a safety factor of 2-5 to the design of collimator shielding and patient dose sparing, the ZAP-X delivers less than 10% of the patient whole body dose compared to this standard, originating from the X-ray target. Even though the ZAP-X intensity modulated radiation therapy (IMRT) factor is significantly higher than conventional Linacs, the absolute dose originating from leakage radiation remains lower by 25. The amount of unintended dose received by the patient's body distant from the isocenter is of interest from the perspective of both clinical and radiation safety. As this whole-body dose is decreased, the resulting treatment-related cancer incidence and mortality rates are decreased accordingly.

ImmunoPET: IMaging of cancer imMUNOtherapy targets with positron Emission Tomography: a phase 0/1 study characterising PD-L1 with 89Zr-durvalumab (MEDI4736) PET/CT in stage III NSCLC patients receiving chemoradiation study protocol

BackgroundImmunoPET is a multicentre, single arm, phase 0–1 study that aims to establish if 89Zr-durvalumab PET/CT can be used to interrogate the expression of PD-L1 in larger, multicentre clinical trials.MethodsThe...

Preclinical development of ZED8, an 89Zr immuno-PET reagent for monitoring tumor CD8 status in patients undergoing cancer immunotherapy.

ZED8 is a novel monovalent antibody labeled with zirconium-89 for the molecular imaging of CD8. This work describes nonclinical studies performed in part to provide rationale for and to inform expectations in the early clinical development of ZED8, such as in the studies outlined in clinical trial registry NCT04029181 [1]. Surface plasmon resonance, X-ray crystallography, and flow cytometry were used to characterize the ZED8-CD8 binding interaction, its specificity, and its impact on T cell function. Immuno-PET with ZED8 was assessed in huCD8+ tumor-bearing mice and in non-human primates. Plasma antibody levels were measured by ELISA to determine pharmacokinetic parameters, and OLINDA 1.0 was used to estimate radiation dosimetry from image-derived biodistribution data. ZED8 selectively binds to human CD8α at a binding site approximately 9Å from that of MHCI making mutual interference unlikely. The equilibrium dissociation constant (KD) is 5nM. ZED8 binds to cynomolgus CD8 with reduced affinity (66nM) but it has no measurable affinity for rat or mouse CD8. In a series of lymphoma xenografts, ZED8 imaging was able to identify different CD8 levels concordant with flow cytometry. In cynomolgus monkeyswith tool compound89Zr-aCD8v17, lymph nodes were conspicuous by imaging 24h post-injection, and the pharmacokinetics suggested a flat-fixed first-in-human dose of 4mg per subject. The whole-body effective dose for an adult human was estimated to be 0.48mSv/MBq, comparable to existing 89Zr immuno-PET reagents. 89Zr immuno-PET with ZED8 appears to be a promising biomarker of tissue CD8 levels suitable for clinical evaluation in cancer patients eligible for immunotherapy.

A simple analytical model for a fast 3D assessment of peripheral photon dose during coplanar isocentric photon radiotherapy.

Considering that cancer survival rates have been growing and that nearly two-thirds of those survivors were exposed to clinical radiation during its treatment, the study of long-term radiation effects, especially secondary cancer induction, has become increasingly important. To correctly assess this risk, knowing the dose to out-of-field organs is essential. As it has been reported, commercial treatment planning systems do not accurately calculate the dose far away from the border of the field; analytical dose estimation models may help this purpose. In this work, the development and validation of a new three-dimensional (3D) analytical model to assess the photon peripheral dose during radiotherapy is presented. It needs only two treatment-specific input parameter values, plus information about the linac-specific leakage, when available. It is easy to use and generates 3D whole-body dose distributions and, particularly, the dose to out-of-field organs (as dose–volume histograms) outside the 5% isodose for any isocentric treatment using coplanar beams [including intensity modulated radiotherapy and volumetric modulated arc therapy (VMAT)]. The model was configured with the corresponding Monte Carlo simulation of the peripheral absorbed dose for a 6 MV abdomen treatment on the International Comission on Radiological Protection (ICRP) 110 computational phantom. It was then validated with experimental measurements using thermoluminescent dosimeters in the male ATOM anthropomorphic phantom irradiated with a VMAT treatment for prostate cancer. Additionally, its performance was challenged by applying it to a lung radiotherapy treatment very different from the one used for training. The model agreed well with measurements and simulated dose values. A graphical user interface was developed as a first step to making this work more approachable to a daily clinical application.

Manual Versus Artificial Intelligence-Based Segmentations as a Pre-processing Step in Whole-body PET Dosimetry Calculations

PurposeAs novel tracers are continuously under development, it is important to obtain reliable radiation dose estimates to optimize the amount of activity that can be administered while keeping radiation burden within acceptable limits.Organ segmentation is required for quantification of specific uptake in organs of interest and whole-body dosimetry but is a time-consuming task which induces high interobserver variability. Therefore, we explored using manual segmentations versus an artificial intelligence (AI)-based automated segmentation tool as a pre-processing step for calculating whole-body effective doses to determine the influence of variability in volumetric whole-organ segmentations on dosimetry.ProceduresPET/CT data of six patients undergoing imaging with 89Zr-labelled pembrolizumab were included. Manual organ segmentations were performed, using in-house developed software, and biodistribution information was obtained. Based on the activity biodistribution information, residence times were calculated. The residence times served as input for OLINDA/EXM version 1.0 (Vanderbilt University, 2003) to calculate the whole-body effective dose (mSv/MBq).Subsequently, organ segmentations were performed using RECOMIA, a cloud-based AI platform for nuclear medicine and radiology research. The workflow for calculating residence times and whole-body effective doses, as described above, was repeated.ResultsData were acquired on days 2, 4, and 7 post-injection, resulting in 18 scans. Overall analysis time per scan was approximately 4 h for manual segmentations compared to ≤ 30 min using AI-based segmentations. Median Jaccard similarity coefficients between manual and AI-based segmentations varied from 0.05 (range 0.00–0.14) for the pancreas to 0.78 (range 0.74–0.82) for the lungs. Whole-body effective doses differed minimally for the six patients with a median difference in received mSv/MBq of 0.52% (range 0.15–1.95%).ConclusionThis pilot study suggests that whole-body dosimetry calculations can benefit from fast, automated AI-based whole organ segmentations.

Protective effect of pycnogenol against gamma radiation-induced lung injury in rat: DNA damage, lipid peroxidation, antioxidant levels, and histopathological changes.

The study aims to evaluate the histopathological changes, enzymatic alterations, and DNA damage in rat lungs induced by whole-body gamma irradiation as well as evaluation of the protective effect of pycnogenol. A hundred adult male rats were equally divided into ten groups including control, four antioxidants, γ-irradiation, four antioxidant + γ-irradiations. This study began the day before radiation treatment and continued for 3 days. The pycnogenol was dissolved 5% dimethyl sulfoxide and then administered orally through a gastric tube at a dose of 37.5 mg/kg, 75 mg/kg, 150 mg/kg, and 300 mg/kg in 24, 48, and 72 h before irradiation. Irradiation was applied with a whole-body irradiation dose of 900 cGy in one fraction. DNA damage, histopathological changes, catalase (CAT), and superoxide dismutase (SOD) activities and malondialdehyde (MDA) levels in lung tissue of rats were evaluated 3 days after irradiation. CAT and SOD activities were found to be significantly lower in the irradiation group than control (P < 0.001). CAT and SOD activities were higher in the antioxidant + γ-irradiation group than both irradiation and control groups. MDA levels were significantly higher in the irradiation group compared to control (P < 0.001), whereas MDA levels decreased in the antioxidant + γ-irradiation group compared to the irradiation group. The antioxidant groups were significantly increased comet parameters depend on pycnogenol doses compared to control. The antioxidant + γ-irradiation was decreased comet parameter compared to γ-irradiation. As a result of the histopathologically, the antioxidant groups were different than the control group that in the areas of alveolar sacs and connective tissue areas were seen hemorrhage areas similar to the irradiation group. We demonstrate that 300 mg/kg of pycnogenol might provide significant protection against deleterious effects from whole-body ionizing radiation on the lung tissue. P300+ γ-ray group was significantly reduced radiation-induced lung injury and was possible to observe significantly preservation.

Updated findings from the International Nuclear Workers Study (INWORKS)

BACKGROUND Despite being a recognized carcinogen, public exposure to ionizing radiation has increased in recent decades. An update to the International Nuclear Workers Study (INWORKS) is being undertaken to strengthen direct assessments of the risks from low dose, low dose rate exposure to penetrating forms of ionizing radiation. Follow-up has been extended by 10 or more years in each partner country. METHODS We are conducting a pooled analysis of cohort mortality studies of nuclear industry workers in the United Kingdom, France, and the United States of America. Individual annual estimates of whole-body dose due to external exposure to penetrating radiation are derived from personal occupational exposure monitoring data. Vital status has been ascertained through 2012, 2014, and 2016 for workers in the United Kingdom, France, and the United States of America, respectively. RESULTS The updated pooled study includes 309,932 workers and 10.7 million person-years of observation. Over the period of follow-up, there have been 103,553 deaths observed, of which 31,009 are deaths due to cancer. CONCLUSIONS This presentation will describe the motivation for an update of the INWORKS study, the major aims of the project, and the progress that we have made to-date. We will report on a major update of this highly-influential study; the person-time in INWORKS increases by a factor of 1.3 and the number of cancer deaths increases by a factor of 1.6. The updated INWORKS analyses will provide some of the most informative direct estimates of low dose radiation risks reported to-date.

Applications of a patient-specific whole-body CT-mesh hybrid computational phantom in second cancer risk prediction

Objective. CT-mesh hybrid phantoms (or ‘hybrid(s)’) made from integrated patient CT data and mesh-type reference computational phantoms (MRCPs) can be beneficial for patient-specific whole-body dose evaluation, but this benefit has yet to be evaluated for second cancer risk prediction. The purpose of this study is to compare the hybrid’s ability to predict risk throughout the body with a patient-scaled MRCP against ground truth whole-body CTs (WBCTs). Approach. Head and neck active scanning proton treatment plans were created for and simulated on seven hybrids and the corresponding scaled MRCPs and WBCTs. Equivalent dose throughout the body was calculated and input into five second cancer risk models for both excess absolute and excess relative risk (EAR and ERR). The hybrid phantom was evaluated by comparing equivalent dose and risk predictions against the WBCT. Main results. The hybrid most frequently provides whole-body second cancer risk predictions which are closer to the ground truth when compared to a scaled MRCP alone. The performance of the hybrid relative to the scaled MRCP was consistent across ERR, EAR, and all risk models. For all in-field organs, where the hybrid shares the WBCT anatomy, the hybrid was better than or equal to the scaled MRCP for both equivalent dose and risk prediction. For out-of-field organs across all patients, the hybrid’s equivalent dose prediction was superior than the scaled MRCP in 48% of all comparisons, equivalent for 34%, and inferior for 18%. For risk assessment in the same organs, the hybrid’s prediction was superior than the scaled MRCP in 51.8% of all comparisons, equivalent in 28.6%, and inferior in 19.6%. Significance. Whole-body risk predictions from the CT-mesh hybrid have shown to be more accurate than those from a reference phantom alone. These hybrids could aid in risk-optimized treatment planning and individual risk assessment to minimize second cancer incidence.

Radiation exposure to extremities in medical applications and its implications for the radiation protection of workers in the Philippines

In medical applications, non-homogeneous radiation exposure conditions may be encountered and whole-body monitoring alone may not be an adequate assessment of doses received by workers. This paper investigated the exposure to extremities in medical applications in the Philippines in terms of personal dose equivalent Hp(0.07). Profiles of monitored workers, dose levels, implications on optimization of occupational exposures, and factors affecting the extremity monitoring implementation were studied. The results show that <3% of workers are monitored for extremities, and there is no monitoring of eye lens dose. There is no extremity monitoring in diagnostic radiology, particularly interventional radiology. Dose levels to extremities were higher and more varied than whole-body doses. In nuclear medicine, the median annual extremity dose is 1.2 mSv, the interquartile range (IQR) is 7.6 mSv (Q1 = 0.5 mSv, Q3 = 8.1 mSv), and the maximum dose is 35 mSv. These median and IQR dose values are four and eight times higher, respectively, compared to the whole-body dose. In radiopharmaceutical distribution, the extremity median annual dose is five times higher than the whole-body dose, and the IQR value is 12 times higher where IQR is 12.1 mSv (Q1 = 0.1 mSv, Q3 = 12.2 mSv). Most notable is in cyclotron operations where <40% of workers were monitored on their extremities; however, the median dose is 100 times higher than the whole-body dose, with a maximum dose of 148 mSv. The results imply that there may be an underassessment of occupational exposure of workers in medical applications. As monitoring results are used for the establishment of a radiation protection program, lack of consideration of extremity doses can lead to inadequate measures in the optimization of worker protection. This study thus shows the need to enhance the implementation of extremity and eye lens dose monitoring in the Philippines to further strengthen the radiation protection of workers in medical applications.

Personal dosimetry for positron emitters, and occupational exposures from clinical use of gallium-68

The current status and issues regarding positron dosimetry in nuclear medicine are summarized. The suitability of the United Kingdom Health Security Agency extremity and eye beta-gamma personal thermoluminescence dosemeters are then considered. Monte Carlo modelling is performed to determine their responses and derive sets of calibration factors, along with H p(0.07) and H p(3) conversion coefficients, for carbon-11, nitrogen-13, oxygen-15, fluorine-18 and gallium-68 sources, which are commonly used in positron emission tomography (PET) computed tomography; data for these isotopes is assumed extrapolatable to other positron sources. It is found that the dosemeters are adequate for assessing exposures to PET radionuclides, even if their routine calibrations to caesium-137 were maintained. An idealized set of measurements representing gallium-68 exposure scenarios is then described, including reproducible mock-ups of individuals manipulating vials and syringes. Finally, a short case-study is presented that explores occupational doses during routine clinical use of gallium-68. The extremity dosemeter results demonstrated significant variations dependent upon the exposure conditions, with some seen to be comparatively large; whole-body and eye dose rates per activity were found to be lower. The importance of routine dose monitoring of workers is emphasized, with the need for a longer-termed follow-up study demonstrated.

Effects of internal exposure to neutron-activated 56MnO2 powder on locomotor activity in rats.

At the detonation of the atomic bombing in Hiroshima and Nagasaki, a significant amount of radionuclides was produced by the neutron induced activation. The residual radiation from the explosion is crucial to the health risk of the people who entered these cities after the bombing and might have inhaled these radioactive materials. Because 56Mn is one of the major radionuclides produced in soil and have not been studied until now, we had conducted a series of experiments using rats to investigate the biological impacts of exposure of 56MnO2 particles. In these experiments, the rats’ spontaneous locomotor activity was also assessed to examine the possible effects of 56Mn on their behavior. However, the locomotor activity data obtained from an individual experiment failed to identify radiation effects due to the large variation among animals and the small sample size. In the present study, all available data from our previous studies on 56MnO2 exposure (0.02–0.15 Gy of whole-body doses) as well as 60Co-γ exposure (at 2–5 Gy of whole-body doses) were pooled. Our statistical method, which takes into account individual differences and daily fluctuations, successfully identified a decrease in locomotor activity caused by 56MnO2 exposure, where the changes were gradual and reached the maximum reduction around 2 weeks after exposure. In contrast, exposure to 60Co-γ rays produced the highest decline of activity within one day. These results suggest that internal exposure to 56Mn at whole-body doses of even less than 0.15 Gy may have a long-lasting impact on locomotor activity.

A model to determine at-home restrictions for cats after treatment of hyperthyroidism with radioiodine.

Felinehyperthyroidism is the most common endocrine disease of older cats and radioiodine is considered to be the gold standard treatment. Isolation periods following treatment vary depending on both individual treatment facilities and the relevant legislation of the country; therefore, there is no recognised standardised protocol defining the length of isolation. This work describes how our institution validated that its owner restrictions met dose constraints by using a model of iodine retention to calculate the required duration and nature of owner restrictions. The retained radioactivity of cats at the point of discharge was used to simulate the radiation dose to owners in the 90 days following release. The model created was used to calculate the minimum duration of isolation for a range of administered activities and owner restrictions. Using the model, it was found that when injected with the maximum dose used, 222 MBq radioiodine, it was possible to release cats after 14 days of isolation and keep owner doses below 0.30 mSv (whole-body effective dose constraint for a single radiation source) with some restrictions. It was possible to release after 23 days with no restrictions. The present study provides clinicians with a consistent and verified method in which they can calculate the isolation periods for radioiodine-treated cats.

Evaluation of pediatric malignancies using total-body PET/CT with half-dose [18F]-FDG.

To explore the impact of a true half dose of [18F]-FDG on image quality in pediatric oncological patients undergoing total-body PET/CT and investigate short acquisition times with half-dose injected activity. One hundred pediatric oncological patients who underwent total-body PET/CT using the uEXPLORER scanner after receiving a true half dose of [18F]-FDG (1.85MBq/kg) were retrospectively enrolled. The PET images were first reconstructed using complete 600-s data and then split into 300-s, 180-s, 60-s, 40-s, and 20-s duration groups (G600 to G20). The subjective analysis was performed using 5-point Likert scales. Objective quantitative metrics included the maximum standard uptake value (SUVmax), SUVmean, standard deviation (SD), signal-to-noise ratio (SNR), and SNRnorm of the background. The variabilities in lesion SUVmean, SUVmax, and tumor-to-background ratio (TBR) were also calculated. The overall image quality scores in the G600, G300, G180, and G60 groups were 4.9 ± 0.2, 4.9 ± 0.3, 4.4 ± 0.5, and 3.5 ± 0.5 points, respectively. All the lesions identified in the half-dose images were localized in the G60 images, while 56% of the lesions could be clearly identified in the G20 images. With reduced acquisition time, the SUVmax and SD of the backgrounds were gradually increased, while the TBR values showed no statistically significant differences among the groups (all p > 0.1). Using the half-dose images as a reference, the variability in the lesion SUVmax gradually increased from the G180 to G20 images, while the lesion SUVmean remained stable across all age groups. SNRnorm was highly negatively correlated with age. Total-body PET/CT with a half dose of [18F]-FDG (1.85MBq/kg, estimated whole-body effective dose: 1.76-2.57mSv) achieved good performance in pediatric patients, with sufficient image quality and good lesion conspicuity. Sufficient image quality and lesion conspicuity could be maintained at a fast scanning time of 60s with half-dose activity.

Development of the DICOM-based Monte Carlo dose reconstruction system for a retrospective study on the secondary cancer risk in carbon ion radiotherapy

Objective. A retrospective study on secondary cancer risk on carbon ion radiotherapy (CIRT) is ongoing at the Heavy Ion Medical Accelerator in Chiba (HIMAC). The reconstruction of the whole-body patient dose distribution is the key issue in the study because dose distribution only around the planning target volume was evaluated in the treatment planning system. Approach. We therefore developed a new dose reconstruction system based on the Particle and Heavy Ion Transport code System (PHITS) coupled with the treatment plan DICOM data set by extending the functionalities of RadioTherapy package based on PHITS (RT-PHITS). In the system, the geometry of patient-specific beam devices such as the range shifter, range compensator, and collimators as well as the individual patient’s body are automatically reconstructed. Various functions useful for retrospective analysis on the CIRT are implemented in the system, such as those for separately deducing dose contributions from different secondary particles and their origins. Main results. The accuracy of the developed system was validated by comparing the dose distribution to the experimental data measured in a water tank and using a treatment plan on an anthropomorphic phantom. Significance. The extended RT-PHITS will be used in epidemiological studies based on clinical data from HIMAC.