Calculate Organ Doses Research Articles

Prior-image-based low-dose CT reconstruction for adaptive radiation therapy.

The study aims to reduce the imaging radiation dose in Adaptive Radiotherapy (ART) while maintaining high-quality CT images, critical for effective treatment planning and monitoring. We developed the Prior-aware Learned Primal-Dual Network (pLPD-UNet), which uses prior CT images to enhance reconstructions from low-dose scans. The network was separately trained on thorax and abdomen datasets to accommodate the unique imaging requirements of each anatomical region. The pLPD-UNet demonstrated improved reconstruction accuracy and robustness in handling sparse data compared to traditional methods. It effectively maintained image quality essential for precise organ delineation and dose calculation, while achieving a significant reduction in radiation exposure. This method offers a significant advancement in the practice of ART by integrating prior imaging data, potentially setting a new standard for balancing radiation safety with the need for high-resolution imaging in cancer treatment planning.

2128: Individual organ dose calculations from CT imaging of Hodgkin lymphoma patients treated with protons

2128: Individual organ dose calculations from CT imaging of Hodgkin lymphoma patients treated with protons

PND-Net: Physics-Inspired Non-Local Dual-Domain Network for Metal Artifact Reduction.

Metal artifacts caused by the presence of metallic implants tremendously degrade the quality of reconstructed computed tomography (CT) images and therefore affect the clinical diagnosis or reduce the accuracy of organ delineation and dose calculation in radiotherapy. Although various deep learning methods have been proposed for metal artifact reduction (MAR), most of them aim to restore the corrupted sinogram within the metal trace, which removes beam hardening artifacts but ignores other components of metal artifacts. In this paper, based on the physical property of metal artifacts which is verified via Monte Carlo (MC) simulation, we propose a novel physics-inspired non-local dual-domain network (PND-Net) for MAR in CT imaging. Specifically, we design a novel non-local sinogram decomposition network (NSD-Net) to acquire the weighted artifact component and develop an image restoration network (IR-Net) to reduce the residual and secondary artifacts in the image domain. To facilitate the generalization and robustness of our method on clinical CT images, we employ a trainable fusion network (F-Net) in the artifact synthesis path to achieve unpaired learning. Furthermore, we design an internal consistency loss to ensure the data fidelity of anatomical structures in the image domain and introduce the linear interpolation sinogram as prior knowledge to guide sinogram decomposition. NSD-Net, IR-Net, and F-Net are jointly trained so that they can benefit from one another. Extensive experiments on simulation and clinical data demonstrate that our method outperforms state-of-the-art MAR methods.

Accuracy of patient-specific CT organ doses from Monte Carlo simulations: influence of CT-based voxel models

Monte Carlo simulations using patient CT images as input are the gold standard to perform patient-specific dosimetry. However, in standard clinical practice patient’s CT images are limited to the reconstructed CT scan range. In this study, organ dose calculations were performed with ImpactMC for chest and cardiac CT using whole-body and anatomy-specific voxel models to estimate the accuracy of CT organ doses based on the latter model. When the 3D patient model is limited to the CT scan range, CT organ doses from Monte Carlo simulations are the most accurate for organs entirely in the field of view. For these organs only the radiation dose related to scatter from the rest of the body is not incorporated. For organs lying partially outside the field of view organ doses are overestimated by not accounting for the non-irradiated tissue mass. This overestimation depends strongly on the amount of the organ volume located outside the field of view. To get a more accurate estimation of the radiation dose to these organs, the ICRP reference organ masses and densities could form a solution. Except for the breast, good agreement in dose was found for most organs. Voxel models generated from clinical CT examinations do not include the overscan in the z-direction. The availability of whole-body voxel models allowed to study this influence as well. As expected, overscan induces slightly higher organ doses.

Radiation exposure of patients from computed tomography for COVID-19 diagnosis

BackgroundDuring the global Coronavirus Disease 2019 (COVID-19) pandemic, numerous computed tomography (CT) scans were conducted to assess pulmonary abnormalities associated with COVID-19. A number of studies have contributed to our current understanding of radiation doses in the context of chest CT scans for COVID-19 diagnosis, but there remains a discernible gap in the literature regarding organ-level dose assessments. Materials and methodsWe estimated organ and effective dose for the COVID-19-related chest CT patients in the following three steps. First, we collected CTDIvol and DLP from the literature published during and after COVID-19 pandemic period. Second, we developed the probability density functions (PDFs) for the CTDIvol and the starting location of CT scans by age groups from which 1000 sets of patient and technique parameters were created. With CT organ dose calculation software, National Cancer Institute dosimetry system for CT (NCICT), we calculated 1000 sets of plausible organ and effective doses and evaluated summary statistics for the patient population. ResultsThe standard dose protocol administered approximately five times higher CTDIvol (5.4 mGy) to patients undergoing COVID-19-related chest CT scans compared to the low dose protocol (1.1 mGy). The median lung dose (11.8 mGy) for the 1-year-old patients was about 1.5 times greater than that (7.8 mGy) of the adult patients. We found that 75% of whole COVID-19-related CT patients would have received effective doses less than 6.4 mSv and 1.5 mSv when scanned by standard dose and low dose protocols, respectively. ConclusionWe evaluated the distribution of organ and effective dose for the COVID-19-related chest CT patients worldwide by collecting comprehensive data of CTDIvol for the COVID-19-related chest CT scans from the literature and combining them with NCICT organ dose calculator. While past studies have predominantly reported basic CT dose descriptors, our work takes it a step further by reporting organ-level doses and effective doses. Subsequent research endeavors could involve enhancing the precision of radiation dose assessment through the collection of a subset of electronic CT records.

Pediatric phantom library constructed from ICRP mesh-type reference computational phantoms (MRCPs)

International Commission on Radiological Protection (ICRP) recently developed the adult and pediatric mesh-type reference computational phantoms (MRCPs) in high-quality/fidelity mesh format, featuring high deformability into various body sizes and poses. Utilizing this feature, the adult MRCPs-based body-size-dependent phantom library was developed for individualized dosimetry. To complete the full phantom library set, the present study produced the pediatric-MRCPs-based body-size-dependent pediatric phantom library. The library comprises a total of 637 phantoms (356 males and 281 females) with varying standing heights and body weights, covering a wide range of body sizes (i.e., including from 1st to 99th percentile height and weight values) for infants, children, and adolescents, offering a realistic representation of body shapes by reflecting ten secondary anthropometric parameters. The phantoms were automatically constructed utilizing automatic deformation program. The dosimetric impact of the library was investigated by calculating organ doses for external exposures to broad parallel photon beams in anterior-posterior direction. Compared with the values of the pediatric MRCPs, significant differences were observed at energies <0.05 MeV, showing larger values for underweight phantom and smaller values for obese phantom. The results highlight the importance of using the pediatric phantom library for accurate dose estimates of individual children with various body sizes.

Reconstruction of organ doses for patients undergoing computed tomography examinations in Canada 1992-2019.

We derived the first comprehensive organ dose library for Canadian pediatric and adult patients who underwent computed tomography (CT) scans between 1992 and 2019 to support epidemiological analysis of radiation risk. We calculated organ absorbed doses for Canadian CT patients in two steps. First, we modeled Computed Tomography Dose Index (CTDI) values by patient age, scan body part, and scan year for the scan period between 1992 and 2019 using national survey data conducted in Canada and partially the United Kingdom survey data as surrogates. Second, we converted CTDI values to organ absorbed doses using a library of organ dose conversion coefficients built in an organ dose calculation program, the National Cancer Institute dosimetry system for CT. In result, we created a library of doses delivered to 33 organs and tissues by different patient ages and genders, scan body parts and scan years. In the scan period before 2000, the organs receiving the greatest dose in the head, chest and abdomen-pelvis scans were the active marrow (3.7-15.2mGy), lungs (54.7-62.8mGy) and colon (54.9-68.5mGy), respectively. We observed organ doses reduced by 24% (pediatric head and torso scans, and adult head scans) and 55% (adult torso scans) after 2000. The organ dose library will be used to analyse the risk of radiation exposure from CT scans in the Canadian CT patient cohort.

A Review of Organ Dose Calculation Methods and Tools for Patients Undergoing Diagnostic Nuclear Medicine Procedures

Exponential growth has been observed in nuclear medicine procedures worldwide in the past decades. The considerable increase is attributed to the advance of positron emission tomography and single photon emission computed tomography, as well as the introduction of new radiopharmaceuticals. Although nuclear medicine procedures provide undisputable diagnostic and therapeutic benefits to patients, the substantial increase in radiation exposure to nuclear medicine patients raises concerns about potential adverse health effects and calls for the urgent need to monitor exposure levels. In the current article, model-based internal dosimetry methods were reviewed, focusing on Medical Internal Radiation Dose (MIRD) formalism, biokinetic data, human anatomy models (stylized, voxel, and hybrid computational human phantoms), and energy spectrum data of radionuclides. Key results from many articles on nuclear medicine dosimetry and comparisons of dosimetry quantities based on different types of human anatomy models were summarized. Key characteristics of seven model-based dose calculation tools were tabulated and discussed, including dose quantities, computational human phantoms used for dose calculations, decay data for radionuclides, biokinetic data, and user interface. Lastly, future research needs in nuclear medicine dosimetry were discussed. Model-based internal dosimetry methods were reviewed focusing on MIRD formalism, biokinetic data, human anatomy models, and energy spectrum data of radionuclides. Future research should focus on updating biokinetic data, revising energy transfer quantities for alimentary and gastrointestinal tracts, accounting for body size in nuclear medicine dosimetry, and recalculating dose coefficients based on the latest biokinetic and energy transfer data.

CBCT-Based synthetic CT image generation using conditional denoising diffusion probabilistic model.

Daily or weekly cone-beam computed tomography (CBCT) scans are commonly used for accurate patient positioning during the image-guided radiotherapy (IGRT) process, making it an ideal option for adaptive radiotherapy (ART) replanning. However, the presence of severe artifacts and inaccurate Hounsfield unit (HU) values prevent its use for quantitative applications such as organ segmentation and dose calculation. To enable the clinical practice of online ART, it is crucial to obtain CBCT scans with a quality comparable to that of a CT scan. This work aims to develop a conditional diffusion model to perform image translation from the CBCT to the CT distribution for the image quality improvement of CBCT. The proposed method is a conditional denoising diffusion probabilistic model (DDPM) that utilizes a time-embedded U-net architecture with residual and attention blocks to gradually transform the white Gaussian noise sample to the target CT distribution conditioned on the CBCT. The model was trained on deformed planning CT (dpCT) and CBCT image pairs, and its feasibility was verified in brain patient study and head-and-neck (H&N) patient study. The performance of the proposed algorithm was evaluated using mean absolute error (MAE), peak signal-to-noise ratio (PSNR) and normalized cross-correlation (NCC) metrics on generated synthetic CT (sCT) samples. The proposed method was also compared to four other diffusion model-based sCT generation methods. In the brain patient study, the MAE, PSNR, and NCC of the generated sCT were 25.99 HU, 30.49dB, and 0.99, respectively, compared to 40.63 HU, 27.87dB, and 0.98 of the CBCT images. In the H&N patient study, the metrics were 32.56 HU, 27.65dB, 0.98 and 38.99 HU, 27.00, 0.98 for sCT and CBCT, respectively. Compared to the other four diffusion models and one Cycle generative adversarial network (Cycle GAN), the proposed method showed superior results in both visual quality and quantitative analysis. The proposed conditional DDPM method can generate sCT from CBCT with accurate HU numbers and reduced artifacts, enabling accurate CBCT-based organ segmentation and dose calculation for online ART.

Presentation of Organ Dose and Effective Dose Conversion Factors in Dual-Energy Computed Tomography: A Monte Carlo Simulation Study.

The same conversion factors (k-factors) of Single CT (SECT) are applied to estimate the Effective Dose (ED) in Dual Energy Computed Tomography (DECT). However, k-factors for different organs need independently validating for DECT, due to the different conditions in DECT. This study aimed to calculate organ dose and k-factors in different imaging protocols (liver, chest, cardiac, and abdomen) for male and female phantoms. This Monte Carlo Simulation study used Monte Carlo N-Particle (MCNP) code for modeling a Siemens Somatom Definition Flash dual-source CT scanner. The organ dose, dose length product, and k-factors were calculated for the Medical Internal Radiation Dose (MIRD) of male and female phantoms. For the male phantom, the k-factors for the liver, chest, cardiac, and abdomen-pelvis imaging protocols are equal to 0.020, 0.012, 0.016, and 0.014 mSv.mGy-1cm-1, respectively. For the female phantom, the corresponding values are equal to 0.026, 0.023, 0.036, and 0.018, respectively. These values for DECT are different from those corresponding values for SECT, especially for the female phantom. The calculated k-factors for DECT can be used as reference values for the estimation of ED in DECT.

Report on the PET/CT Image-Based Radiation Dosimetry of [18F]FDHT in Women, a Validated Imaging Agent with New Applications for Evaluation of Androgen Receptor Status in Women with Metastatic Breast Cancer.

In a prospective clinical trial, [18F]fluoro-5α-dihydrotestosterone ([18F]FDHT), the radiolabeled analog of the androgen dihydrotestosterone, was used as a PET/CT imaging agent for invivo assessment of metastatic androgen receptor-positive breast cancer in postmenopausal women. To our knowledge, this article presents the first report of PET/CT image-based radiation dosimetry of [18F]FDHT in women. Methods: [18F]FDHT PET/CT imaging was performed on a cohort of 11 women at baseline before the start of therapy and at 2 additional time points during selective androgen receptor modulator (SARM) therapy for androgen receptor-positive breast cancer. Volumes of interest (VOIs) were placed over the whole body and within source organs seen on the PET/CT images, and the time-integrated activity coefficients of [18F]FDHT were derived. The time-integrated activity coefficients for the urinary bladder were calculated using the dynamic urinary bladder model in OLINDA/EXM software, with biologic half-life for urinary excretion derived from VOI measurements of the whole body in postvoid PET/CT images. The time-integrated activity coefficients for all other organs were calculated from VOI measurements in the organs and the physical half-life of 18F. Organ dose and effective dose calculations were then performed using MIRDcalc, version 1.1. Results: At baseline before SARM therapy, the effective dose for [18F]FDHT in women was calculated as 0.020 ± 0.0005 mSv/MBq, and the urinary bladder was the organ at risk, with an average absorbed dose of 0.074 ± 0.011 mGy/MBq. Statistically significant decreases in liver SUV or uptake of [18F]FDHT were found at the 2 additional time points on SARM therapy (linear mixed model, P < 0.05). Likewise, absorbed dose to the liver also decreased by a small but statistically significant amount at the 2 additional time points (linear mixed model, P < 0.05). Neighboring abdominal organs of the gallbladder wall, stomach, pancreas, and adrenals also showed statistically significant decreases in absorbed dose (linear mixed model, P < 0.05). The urinary bladder wall remained the organ at risk at all time points. Absorbed dose to the urinary bladder wall did not show statistically significant changes from baseline at any of the time points (linear mixed model, P ≥ 0.05). Effective dose also did not show statistically significant changes from baseline (linear mixed model, P ≥ 0.05). Conclusion: Effective dose for [18F]FDHT in women before SARM therapy was calculated as 0.020 ± 0.0005 mSv/MBq. The urinary bladder wall was the organ at risk, with an absorbed dose of 0.074 ± 0.011 mGy/MBq.

Monte Carlo calculations of critical organ doses in radioembolization therapy of primary liver tumors via 90Y microspheres

Monte Carlo calculations of critical organ doses in radioembolization therapy of primary liver tumors via 90Y microspheres

NCIRF: an organ dose calculator for patients undergoing radiography and fluoroscopy

Background. It is critical to monitor the radiation dose delivered to patients undergoing radiography and fluoroscopy to prevent both acute and potential long-term adverse health effects. Accurate estimation of organ doses is essential to ensuring that radiation dose is maintained As Low As Reasonably Achievable. We developed a graphical user interface-based organ dose calculation tool for pediatric and adult patients undergoing radiography and fluoroscopy examinations. Methods. Our dose calculator follows the four sequential steps. First, the calculator obtains input parameters related to patient age and gender, and x-ray source data. Second, the program creates an input file describing the anatomy and material composition of a phantom, x-ray source, and organ dose scorers for Monte Carlo radiation transport using the user input parameters. Third, a built-in Geant4 module was developed to import the input file and to calculate organ absorbed doses and skeletal fluences through Monte Carlo radiation transport. Lastly, active marrow and endosteum doses are derived from the skeletal fluences and effective dose is calculated from the organ and tissue doses. Following benchmarking with MCNP6, we conducted some benchmarking calculations calculated organ doses for an illustrative cardeiac interventional fluoroscopy and compared the results with those from an existing dose calculator, PCXMC. Results. The graphical user interface-based program was entitled National Cancer Institute dosimetry system for Radiography and Fluoroscopy (NCIRF). Organ doses calculated from NCIRF showed an excellent agreement with those from MCNP6 in the simulation of an illustrative fluoroscopy exam. In the cardiac interventional fluoroscopy exam of the adult male and female phantoms, the lungs received relatively greater doses than any other organs. PCXMC based on stylistic phantoms overall overestimated major organ doses calculated from NCIRF by up to 3.7-fold (active bone marrow). Conclusion. We developed an organ dose calculation tool for pediatric and adult patients undergoing radiography and fluoroscopy examinations. NCIRF could substantially increase the accuracy and efficiency of organ dose estimation in radiography and fluoroscopy exams.

Estimation of cancer risks due to chest radiotherapy treatment planning computed tomography (CT) simulations.

The objective of our study was to determine organ doses to estimate the lifetime attributable risk (LAR) of cancer incidence related to chest tomography simulations for Radiotherapy Treatment Planning (RTTP) using patient-specific information. Patient data were used to calculate organ doses and effective dose. The effective dose (E) was calculated by two methods. First, to calculate effective dose in a standard phantom, the collected dosimetric parameters were used with the ImPACT CT Patient Dosimetry Calculator and E was calculated by applying related correction factors. Second, using the scanner-derived Dose Length Product, LARs were computed using the US National Academy of Sciences (BEIR VII) model for age- and sex-specific risks at each exposure. DLP, CTDIvol, and scan length were 507 ± 143mGy.cm, 11 ± 4mGy, and 47 ± 7cm, respectively. The effective dose was 10 ± 3mSv using ImPACT patient dosimetry calculator software and 9 ± 2mSv using the scanner-derived Dose Length Product. The LAR of cancer incidence for all cancers, all solid cancers and leukemia were 65 ± 29, 62 ± 27, 7 ± 2 cases per 100,000 individuals, respectively. Radiation exposure from the usage of CT for radiotherapy treatment planning (RTTP) causes non-negligible increases in lifetime attributable risk. The results of this study can be used as a guide by physicians to implement strategies based on the As Low As Reasonably Achievable (ALARA) principle that lead to a reduction dose without sacrificing diagnostic information.

Dose measurement study of the chest during a CT scan using a fabricated phantom

The purpose of this study was to evaluate radiation doses during computer tomography (CT) scans of the whole body and organs using a fabricated phantom. The Weighted Computer Tomography Dose Index (CTDIw) was evaluated and measured using a fabricated phantom, and five CT scanners were used for chest examinations from four hospitals in Najran, Saudi Arabia. The heart, lungs, esophagus, and spinal cord doses were measured with clinical whole body CT acquisition protocol using Thermoluminescent Dosimeters (TLDs). The TLDs used for measurements were selected for an accuracy of 5% and calibrated for the X-ray radiation field. The CTDIw and organ doses reported in this study were compared with results of ImPACT software for calculating organ doses. The results show good agreement with the calculations and the literature. The measured specific organ doses ranged between 1.33 mGy (lung marrow) and 1.65 mGy (esophagus). The model is easy to produce and useful for evaluating the organ doses and CTDIw.

First-in-human imaging using [11C]MDTC: a radiotracer targeting the cannabinoid receptor type 2.

We report findings from the first-in-human study of [11C]MDTC, a radiotracer developed to image the cannabinoid receptor type 2 (CB2R) with positron emission tomography (PET). Ten healthy adults were imaged according to a 90-min dynamic PET protocol after bolus intravenous injection of [11C]MDTC. Five participants also completed a second [11C]MDTC PET scan to assess test-retest reproducibility of receptor-binding outcomes. The kinetic behavior of [11C]MDTC in human brain was evaluated using tissue compartmental modeling. Four additional healthy adults completed whole-body [11C]MDTC PET/CT to calculate organ doses and the whole-body effective dose. [11C]MDTC brain PET and [11C]MDTC whole-body PET/CT was well-tolerated. A murine study found evidence of brain-penetrant radiometabolites. The model of choice for fitting the time activity curves (TACs) across brain regions of interest was a three-tissue compartment model that includes a separate input function and compartment for the brain-penetrant metabolites. Regional distribution volume (VT) values were low, indicating low CB2R expression in the brain. Test-retest reliability of VT demonstrated a mean absolute variability of 9.91%. The measured effective dose of [11C]MDTC was 5.29 μSv/MBq. These data demonstrate the safety and pharmacokinetic behavior of [11C]MDTC with PET in healthy human brain. Future studies identifying radiometabolites of [11C]MDTC are recommended before applying [11C]MDTC PET to assess the high expression of the CB2R by activated microglia in human brain.

Estimation of radiation doses and lifetime attributable risk of radiation-induced cancer in the uterus and prostate from abdomen pelvis CT examinations.

Computed tomography (CT) scans are one of the most common radiation imaging modalities, and CT scans are rising steadily worldwide. CT has the potential to enhance radiography practice, but it also has the risk of drastically increasing patient doses. One CT procedure for the abdomen pelvis (AP) area can expose a patient's prostate or uterus to a substantial radiation dose, leading to concerns about radiation-induced cancer. This study aimed to estimate organ doses of the uterus and prostate and evaluate the lifetime attributable risk (LAR) of cancer incidence and mortality resulting from AP CT examinations. This retrospective study included 665 patients, of which 380 (57%) were female, and 285 (43%) were male. Data were collected from the picture archiving and communication system for AP CT procedures and exposure parameter data. Organ doses for the uterus and prostate were calculated using National Cancer Institute CT (NCICT) software. Based on the risk models proposed by the BEIR VII report, the calculated organ doses were used to estimate the LAR of prostate and uterus cancer incidence and mortality due to radiation exposure from AP CT procedures. The mean effective dose resulting from AP CT for females and males was 5.76 ± 3.22 (range: 1.13-12.71 mSv) and 4.37 ± 1.66 mSv (range: 1.36-8.07 mSv), respectively. The mean organ dose to the uterus was 10.86 ± 6.09 mGy (range: 2.13-24.06 mGy). The mean organ dose to the prostate was 7.00 ± 2.66 mGy (range: 2.18-12.94 mGy). The LAR of uterus and prostate cancer incidence was 1.75 ± 1.19 cases and 2.24 ± 1.06 cases per 100,000 persons, respectively. The LAR of cancer mortality rates from uterus and prostate cancers were 0.36 ± 0.22 and 0.48 ± 0.18 cases per 100,000 persons, respectively. The LAR of prostate and uterus cancer occurrence and mortality from radiation doses with AP CT procedures was low but not trivial. Therefore, efforts should be made to lower patient doses while retaining image quality. Although the minimization of the patient's radiation dose must guide clinical practice, the estimated slight increase in risk could aid in easing fears regarding well-justified AP CT procedures.

ASSESSMENT OF PCXMC MONTE CARLO SIMULATIONS IN SLOT-SCANNING-BASED EXAMINATIONS: COMPARISON WITH IN-PHANTOM THERMOLUMINESCENT DOSIMETRY.

Slot-scanning technology is nowadays a valid solution for the follow-up of chronic musculoskeletal disorders on children and adolescent patients, but there is no commercial software designed for simulating this X-ray beam geometry. PC Program for X-ray Monte Carlo (PCXMC) is a widespread Monte Carlo software developed for dose computation in projection radiography. In this study, experimental measurements were performed to evaluate its applicability in examinations with a slit-beam device. Physical phantoms corresponding to an adult and a 5-y-old child with calibrated thermoluminescent dosemeters were used for experiments. Different simulation approaches were investigated. Differences between measured and calculated organ doses ranged from -95 to 67% and were statistically significant for almost all organs. For both patients, PCXMC underestimated the effective dose of about 25%. This study suggests that PCXMC is not suited for organ dose evaluation in examinations with slot-scanning devices. It is still a useful tool for effective dose estimation when a proper correction factor is applied.

Organ dose calculator for diagnostic nuclear medicine patients based on the ICRP reference voxel phantoms and biokinetic models

The exponential growth in the use of nuclear medicine procedures represents a general radiation safety concern and stresses the need to monitor exposure levels and radiation-related long term health effects in NM patients. In the current study, following our previous work on NCINM version 1 based on the UF/NCI hybrid phantom series, we calculated a comprehensive library of S values using the ICRP reference pediatric and adult voxel phantoms and established a library of biokinetic data from multiple ICRP Publications, which were then implemented into NCINM version 2. We calculated S values in two steps: calculation of specific absorbed fraction (SAF) using a Monte Carlo radiation transport code combined with the twelve ICRP pediatric and adult voxel phantoms for a number of combinations of source and target region pairs; derivation of S values from the SAFs using the ICRP nuclear decay data. We also adjusted the biokinetic data of 105 radiopharmaceuticals from multiple ICRP publications to match the anatomical description of the ICRP voxel phantoms. Finally, we integrated the ICRP phantom-based S values and adjusted biokinetic data into NCINM version 2. The ratios of cross-fire SAFs from NCINM 2 to NCINM 1 for the adult phantoms varied widely from 0.26 to 5.94 (mean = 1.24, IQR = 0.77–1.55) whereas the ratios for the pediatric phantoms ranged from 0.64 to 1.47 (mean = 1.01, IQR = 0.98–1.03). The ratios of absorbed dose coefficients from NCINM 2 over those from ICRP publications widely varied from 0.43 (colon for 99mTc-ECD) to 2.57 (active marrow for 99mTc-MAG3). NCINM 2.0 should be useful for dosimetrists and medical physicists to more accurately estimate organ doses for various nuclear medicine procedures.

CT organ dose calculator size adaptive for pediatric and adult patients

Background. Although computed tomography (CT) has played a critical role in medical care since its introduction in the 1970s, its potential long-term risk of adverse health effects has been of concern. It is crucial to accurately estimate the radiation dose delivered to the patient’s critical organs to ensure the dose is As Low As Reasonably Achievable. However, organ-level dose calculation tools for pediatric and adult patients with various body sizes are rare. We extended the existing CT organ dose calculator, NCICT 1.0, which is based on reference-size phantoms, to include body size-specific pediatric and adult phantoms. Methods. We calculated body size-specific organ doses normalized to CTDIvol by using a library of 158 pediatric and 193 adult computational human phantoms with various body sizes combined with a Monte Carlo radiation transport code, MCNP6. We also created a library of generic tube current modulation (TCM) profiles for the phantom library using a ray-tracing algorithm and implemented them into organ dose calculations. We validated organ doses for the body size-specific phantoms using those calculated from ten abdominal CT patients. We also evaluated potential dosimetric errors caused by only using reference phantoms for patients with different body sizes. Results. Organ dose coefficients and TCM profiles for 351 pediatric and adult body size-specific phantoms were implemented into NCICT 2.0. The dose coefficients from the ten abdominal CT patients agreed with those from the program within 13%. The organ doses for the overweight phantoms were overestimated by over 80% when only reference size phantoms were used. Conclusion. We confirmed that the upgraded dose calculator NCICT 2.0 could substantially reduce potential dosimetric errors caused by using only reference size phantoms. The program should be useful for the radiology community to accurately monitor organ doses for pediatric and adult CT patients with various body sizes.