Dose Estimates Research Articles

Mode of action Criteria for selection of the critical effect and safe dose range for PFOA by the Alliance for risk assessment.

In response to the current disparity in risk assessment values for PFOA from different agencies and countries, an international effort facilitated by the Alliance for Risk Assessment (ARA) was recently undertaken to characterize the range of scientifically supportable safe dose estimates. In this assessment (Burgoon et al., 2023), an evaluation of the evidence regarding the potential modes of action (MOA) for PFOA toxicity was performed first, so that it could be used to inform subsequent decisions regarding potential critical effects and studies. This review describes the evidence considered in the MOA evaluations that were performed as part of the ARA effort. The overall conclusions of this evaluation are that the available mechanistic data do not support any conclusion that reported epidemiological associations of blood concentrations of PFOA as low as 10ng/mL with various health effects should be considered causal. It is more likely that the reported associations may instead reflect reverse causality/pharmacokinetic confounding. These conclusions are consistent with the opinions of the World Health Organization (WHO, 2022).

A mapping-free natural language processing-based technique for sequence search in nanopore long-reads.

In unforeseen situations, such as nuclear power plant's or civilian radiation accidents, there is a need for effective and computationally inexpensive methods to determine the expression level of a selected gene panel, allowing for rough dose estimates in thousands of donors. The new generation in-situ mapper, fast and of low energy consumption, working at the level of single nanopore output, is in demand. We aim to create a sequence identification tool that utilizes natural language processing techniques and ensures a high level of negative predictive value (NPV) compared to the classical approach. The training dataset consisted of RNA sequencing data from 6 samples. Multiple natural language processing models were examined, differing in the type of dictionary components (word length, step, context) as well as the encoding length and number of sequences required for algorithm training. The best configuration analyses the entire sequence and uses a word length of 3 base pairs with one-word neighbor on each side. For the considered FDXR gene, the achieved mean balanced accuracy (BACC) was 98.29% and NPV was 99.25%, compared to minimap2's performance in a cross-validation scenario. The next stage focused on exploring the dictionary components and attempting to optimize it, employing statistical techniques as well as those relying on the explainability of the decisions made. Reducing the dictionary from 1024 to 145 changed BACC to 96.49% and the NPV to 98.15%. Obtained model, validated on an external independent genome sequencing dataset, gave NPV of 99.64% for complete and 95.87% for reduced dictionary. The salmon-estimated read counts differed from the classical approach on average by 3.48% for the complete dictionary and by 5.82% for the reduced one. We conclude that for long Oxford nanopore reads, a natural language processing-based approach can reliably replace classical mapping when there is a need for fast, reliable and energy and computationally efficient targeted mapping of a pre-defined subset of transcripts. The developed model can be easily retrained to identify selected transcripts and/or work with various long-read sequencing techniques. Our results of the study clearly demonstrate the potential of applying techniques known from classical text processing to nucleotide sequences.

Statistical-based modeling strategy for entrance skin dose estimation in patient undergoing body interventional radiology.

Interventional radiology (IR) provides significant advancements in diagnostic and therapeutic procedures, yet concerns persist regarding radiological risks such as erythema, burns, and epilation. Direct dose measurements observed difficulties regarding the perturbation of the detector probe in X-ray images during fluoroscopy-guided procedures, high-cost expenses, and non-compliant patients. This study aims to develop a statistical-based model for estimating entrance skin dose (ESD) in body IR procedures using patient radiation-dose recording data. Models are categorized into vascular and non-vascular procedures. This study demonstrates that the simplified models are sufficient in estimating patient ESDs for both IR groups, with a 95% confidence interval. This user-friendly method enables radiologists to calculate doses without complex parameters such as the backscatter factor and mass-energy absorption coefficient, as required in conventional calculation methods. It not only does this support to radiologists in effectively refining treatment protocols, but also enables patients to monitor their received doses immediately after treatment ends.

Neural Network Ensemble to Detect Dicentric Chromosomes in Metaphase Images

The Dicentric Chromosome Assay (DCA) is widely used in biological dosimetry, where the number of dicentric chromosomes induced by ionizing radiation (IR) exposure is quantified to estimate the absorbed radiation dose an individual has received. Dicentric chromosome scoring is a laborious and time-consuming process which is performed manually in most cytogenetic biodosimetry laboratories. Further, dicentric chromosome scoring constitutes a bottleneck when several hundreds of samples need to be analyzed for dose estimation in the aftermath of large-scale radiological/nuclear incident(s). Recently, much interest has focused on automating dicentric chromosome scoring using Artificial Intelligence (AI) tools to reduce analysis time and improve the accuracy of dicentric chromosome detection. Our study aims to detect dicentric chromosomes in metaphase plate images using an ensemble of artificial neural network detectors suitable for datasets that present a low number of samples (in this work, only 50 images). In our approach, the input image is first processed by several operators, each producing a transformed image. Then, each transformed image is transferred to a specific detector trained with a training set processed by the same operator that transformed the image. Following this, the detectors provide their predictions about the detected chromosomes. Finally, all predictions are combined using a consensus function. Regarding the operators used, images were binarized separately applying Otsu and Spline techniques, while morphological opening and closing filters with different sizes were used to eliminate noise, isolate specific components, and enhance the structures of interest (chromosomes) within the image. Consensus-based decisions are typically more precise than those made by individual networks, as the consensus method can rectify certain misclassifications, assuming that individual network results are correct. The results indicate that our methodology worked satisfactorily in detecting a majority of chromosomes, with remarkable classification performance even with the low number of training samples utilized. AI-based dicentric chromosome detection will be beneficial for a rapid triage by improving the detection of dicentric chromosomes and thereby the dose prediction accuracy.

Radiation dose estimation for indoor radon, thoron and their progenies using a stochastic method-a small-scale survey in Wuhan, China.

Passive radon monitors with CR-39s are widely used in major epidemiological surveys. However, the conventional CR-39 track density determining strategy makes it difficult to accurately estimate the concentration because of the heterogeneity of tracks on CR-39s. This study introduced a stochastic method, Latin hypercube sampling, to improve the track density determining strategy and provide the probability distribution of 222Rn concentration and equilibrium equivalent thoron concentration. The first 222Rn and 220Rn discriminated survey was conducted in Wuhan, China, in 2018 using RADUET® and deposition-based passive 220Rn progeny monitors and applying the stochastic method to the measurement. The results indicate that the stochastic method could decrease the effects of the track heterogeneity on the CR-39s and provide reliable results. The 220Rn progeny contributed more than 40% of the total inhalation dose in the survey, which cannot be ignored in urban family dwellings.

Tube current reduction and iterative image reconstruction for computed tomography myelography.

This study aimed to systematically evaluate the impact of a low-dose (LD) protocol using tube current reduction on image quality, the confidence for intervention planning and guidance, and diagnostic yield for computed tomography (CT)myelography. We retrospectively analyzed 68 patients who underwent CT myelography, with 34 investigations performed with a standard-dose (SD) and 34 investigations performed with a LD protocol (using tube current reduction). The different scans were matched considering variables such as sex, age, presence of spinal instrumentation, and body diameter. All images were evaluated by two readers (R1 and R2) using Likert scales. Image noise was measured using attenuation values of paraspinal muscle tissue. Images were reconstructed with model-based iterative reconstruction (post-myelography diagnostic scans) or hybrid reconstruction (planning, periprocedural, and diagnostic scans). Image quality, overall artifacts, image contrast, and confidence for planning or intervention guidance were rated good to perfect for both SD and LD scans according to evaluations of both readers. Inter-reader agreement was good to very good for the images from intervention planning (κ ≥ 0.80) as well as for intervention guidance (κ ≥ 0.77), as well as for diagnostic scans (κ ≥ 0.85). Image noise was similar between SD and LD scans performed for planning of the interventional procedures (model-based iterative reconstruction: SD 45.37 ± 7.29 HU vs. LD 45.17 ± 9.12 HU; hybrid reconstruction: SD 46.05 ± 7.43 HU vs. LD 45.05 ± 8.69 HU; p > 0.05). The volume-weighted CT dose index (CTDIvol) and size-specific dose estimate (SSDE) were significantly lower for the planning scans as well as the periprocedural scans when using the LD protocol as compared to the SD protocol (p < 0.05). In conclusion,implementation of a LD protocol with tube current reduction for CT myelography is a feasible option to reduce radiation exposure, especially when combined with iterative image reconstruction. In our study, LD imaging did not have a relevant negative impact on image quality, confidence for intervention planning or guidance, or diagnostic certainty for CT myelography.

Chronic bronchitis and bronchial asthma: the impact of chronic occupational radiation exposure on incidence and mortality of Mayak nuclear workers.

The information about the radiation risk of non-cancer respiratory diseases is inconsistent and mainly corresponds to mortality. Previously, an increased risk of chronic bronchitis incidence was demonstrated in the cohort of workers employed at the first Russian nuclear facility Mayak Production Association who had been chronically exposed to gamma rays (externally) and to alpha-active plutonium aerosols (internally). Within this retrospective study, we performed analyses of incidence of and mortality from chronic bronchitis and bronchial asthma using improved estimates of radiation doses provided by the "Mayak Worker Dosimetry System (MWDS) - 2013". The cohort included 22,377 individuals hired in 1948-1982, and its follow-up was extended by 10 years (to the end of 2018). The excess relative risk of chronic bronchitis incidence per unit radiation dose (ERR/Gy) and the 95% confidence interval (95% CI) were: with the 0-year lag ERR/Gy=0.07 (95% CI -0.01, 0.17) for gamma exposure and ERR/Gy=0.36 (95% CI 0.13, 0.68) for alpha exposure; with the 10-year lag ERR/Gy=0.15 (95% CI 0.04, 0.30) for gamma exposure and ERR/Gy=0.54 (95% CI 0.19, 1.03) for alpha exposure. The chronic bronchitis mortality risk was significantly associated with internal alpha exposure only for certain worker categories: ERR/Gy=4.08 (95% CI 0.59, 14.3) in males; ERR/Gy=7.10 (95% CI 0.31, 70.44) in former smokers; ERR/Gy=7.94 (95% CI 1.71, 30.2) in workers with the smoking index above 20 pack×years. No association was observed in the chronic bronchitis mortality risk with external gamma exposure. No strong evidence was observed for the impact of gamma and alpha exposure on risk of mortality from chronic bronchitis. The study confirmed the significant positive linear association of the chronic bronchitis incidence risk with gamma and alpha radiation doses from occupational chronic external and internal exposure. However, the estimates of ERR/Gy of alpha particles from internal exposure appeared to be almost 2.4-3 times lower than those based on the MWDS-2008. The observed inconsistency requires further clarification. As for bronchial asthma in Mayak workers, no association was demonstrated in the incidence and mortality risks with occupational gamma and alpha radiation exposure.

Estimation and analysis of S values for131I using pediatric mesh type reference computational phantoms.

This study examines the effect of paediatric mesh-type reference computational phantoms on organ S values resulting from radioiodine (131I) intake. Using Geant4, we estimated131I S values for 30 radiosensitive target tissues due to emission from the thyroid (Target ← Thyroid) in these phantoms. Our results show that S values differ between male and female phantoms of the same age and S values also decrease as phantom age increases. The male-to-female S value ratio typically varies within 10%, with larger differences observed for the esophagus, extra-thoracic regions, muscles, bladder, and sex organs. On average, S values for mesh phantoms are approximately 17% higher than those for voxel phantoms, with larger discrepancies for organs remodelled separately in mesh phantoms. The study provides organ S values for the paediatric population due to131I exposure from the thyroid, based on reference mesh-type computational phantoms, enhancing organ doses estimation in emergency situations and during radioiodine treatment.

Radiation dose assessment of pediatric computed tomography of the chest: the need to consider patient size.

To evaluate the radiation dose of chest computed tomography (CT) examinations of pediatric patients and the extent to which volume CT dose index (CTDIvol) underestimates radiation dose in comparison to size specific dose estimates (SSDE). Single-center, retrospective study of consecutive unenhanced pediatric (age<18years) chest CTs between October 2015 and October 2016. Radiation dose as well as demographic and clinical data were recorded from 133 chest CTs. Patients were grouped into 4 categories based on mean effective diameter of the chest. SSDE was generated for each patient according to the water equivalent and effective diameter and compared to CTDIvol. Factors associated with higher radiation doses were assessed. CTDIvol underestimated radiation dose by 54.7%, 47.6%, 40.2%, and 31.2% (P<.001) for effective diameter groups 1 to 4, respectively, when compared to SSDE (calculated according to the water equivalent). When calculated according to the effective diameter, CTDIvol underestimated radiation dose by 47.6%, 39.4%, 27%, and 12.3% (P<.001) for effective diameter groups 1 to 4, respectively, when compared to SSDE. CT dose parameters, age, weight, Dw, and mean effective diameter were variables associated with higher radiation doses. CTDIvol systematically underestimated radiation dose in comparison to SSDE in pediatric patients submitted to chest CT and should not be used as the primary parameter to monitor CT protocols in these patients. SSDE calculated according to effective diameter also underestimates the radiation dose compared to SSDE calculated based on water equivalent.

ESTIMATION OF PATIENT RADIATION DOSE WITH SIZE SPECIFIC DOSE ESTIMATE (SSDE) METHOD IN ABDOMEN CT-SCAN EXAMINATION AT SEMEN GRESIK HOSPITAL

CT-Scan abdomen is an examination to see the anatomy and pathology of the abdominal organs, and the scanning image results are in the form of three-dimensional axial images of the body. The radiation dose released from the CT-Scan examination is more significant than other radiology modalities. Therefore, it is very important to estimate the patient's dose accurately. Computed Tomography Dose Index (CTDIvol) and Dose Length Product (DLP) are dose parameters used in CT-Scan to describe the dose value received by the patient. However, these parameters are the output of the CT-Scan, not as the dose received by the patient. The Size Specific Dose Estimate (SSDE) method based on AAPM Report No. 204 is used to determine the estimated dose received by the CT-Scan Abdomen patient. Calculations are done manually and with IndoseCT software. The data used are secondary data of 60 patients, namely 21 females and 39 males, who were on the CT-Scan Abdomen examination without contrast from the Instalasi Radiologi Rumah Sakit Semen Gresik. The SSDE value is obtained from the multiplication between the conversion factor and CTDIvol, where the conversion factor is an effective diameter function. The analysis examined the error value in manual calculations and IndoseCT software in men and women, the relationship between effective diameter and scanning radiation output (CTDIvol), and dose estimation estimates (SSDE). The difference in SSDE values between manual calculations and IndoseCT software was insignificant. The highest error value in women was 3% and 3.2% in men. Meanwhile, the relationship between effective diameter (Deff) and scanning radiation output (CTDIvol) and dose estimation estimates (SSDE) showed that the correlation between effective diameter (Deff) and CTDIvol showed a stronger correlation, namely with R2 around 0.7 in women and men, compared to the correlation between effective diameter (Deff) and SSDE with R2 around 0.03 in women and 0.2 in men. Keywords: CT-Scan, Abdomen, Size Specific Dose Estimate (SSDE).

APPLICATION OF SIZE SPECIFIC DOSE ESTIMATE (SSDE) AS A LOCAL DIAGNOSTIC REFERENCE LEVEL IN HEAD CT SCAN EXAMINATION AT INDRIATI HOSPITAL SOLOBARU, DR. MOEWARDI HOSPITAL SURAKARTA, SLEMAN HOSPITAL, AND NATIONAL BRAIN CENTER HOSPITAL JAKARTA

CT scan is a modality that produces a higher radiation dose compared to other modalities in radiodiagnostic installations. The radiation dose received by patients from examinations with this CT scan device is expressed in the volume CT Dose Index (CTDIvol) and Dose Length Product (DLP), which are dose indicators from the Indonesian Diagnostic Reference Level (DRL) value regulated in the Decree of the Head of the Nuclear Energy Regulatory Agency (BAPETEN) nationally. However, the CTDIvol value is only an indicator of the output dose from the CT scan, and the DLP value is an indicator of the total dose during the examination, which is influenced by the length of the scan. Both do not represent the specific dose received by the patient because the patient's dose depends not only on the output dose but also on the patient's characteristics. The patient's dose, which includes the output dose and patient characteristics, is called the Size-Specific Dose Estimate (SSDE), which is used to estimate the dose received by the patient by including a correction factor depending on the patient's dimensions. This study aims to calculate the SSDE value in a CT Head examination with a standard protocol using the same type of device, namely a 128-slice CT scan in several hospitals. The values of CTDIvol and DLP patients are obtained from the dose report displayed on the CT scan monitor screen in the IndoseCT software. The patient samples studied were patients undergoing CT Head examinations from March 2023 to February 2024, with 100 patients in each hospital. The results of this study obtained local DRL values based on SSDE calculated at Indriati Hospital, Moewardi Hospital, Sleman Hospital, and the National Brain Center Hospital and then compared them with the national TPD values. Based on the SSDE value from Indriati Hospital, the TPD value was 30.26 mGy, Sleman Hospital was 39.5 mGy, Dr. Moewardi Hospital was 49.3 mGy, and RSPON was 51.7 mGy. The TPD value of CT Head examinations without contrast from each hospital was still below the national TPD value of 60 mGy. Keywords: CT scan, diagnostic reference level (DRL), local DRL, national DRL, Size-Specific Dose Estimate (SSDE), IndoseCT.

Comparative analysis of fetal dose sparing between a C-arm linac and an O-ring linac in a SIB-VMAT sarcoma treatment for a pregnant patient: A technical note and case report.

To compare the effect of two linacs designs on fetal dose sparing on a pregnant patient, including estimation of the fetal dose, and the effect of a lead apron. A patient with a high-grade sarcoma located in the right knee/lower thigh was prescribed 51Gy (1.7Gy/Fx) with a simultaneous-integrated-boost (SIB) of 60Gy to a smaller volume, starting in the 26thgestational week. Volumetric modulated radiation therapy (VMAT) plans with 6MV-FFF were developed using identical dosimetric constraints on a Varian Truebeam Edge with HD-MLC and a Varian Halcyon with double-stacked MLC. Based on patient dimension measurements, an anthropomorphic phantom was constructed using a Rando phantom and saline bags in the patient's Vac-Lok bag. Phantom measurements were performed using OSLDs and TLDs placed at three different planes, corresponding to the pubis, the umbilicus, and the fundus based on patient measurements and projected gestational age, to estimate the fetal dose. Three experimental scenarios were measured, each with CBCT-based image guidance for an accurate, reproducible setup: Edge, Halcyon, and Halcyon with a tri-folded lead apron (0.5mm×3=1.5mmPb) over the phantom abdomen. Plan quality and total MUs are comparable between the Edge and Halcyon plans. The OSLD-measured whole-course dose to the pubis, umbilicus, and fundus were 18.8, 13.1, and 11.7 cGy, respectively, on Halcyon, on average 27.8% lower than Edge. The repeatability within either dosimeter was good, although TLD showed systematically lower doses. Importantly, both dosimetry systems showed a lower measured fetal dose for the Halcyon plan compared with the Edge plan. Adding a tri-folded lead apron over the abdomen did not meaningfully lower the measured dose. In this case study, Halcyon demonstrated a better sparing of out-of-field fetal dose compared to TrueBeam Edge. It was shown that lead aprons do not provide additional fetal dose sparing.

Metodología para la validación de programas de cálculo de dosis en piel

Objective. A methodology for facilitating the validation of skin dose estimation programs for interventional procedures is presented. Materials and methods. The methodology uses a series of irradiations stored as DICOM Radiation Dose Structured Reports (RDSRs) as well as reference skin dose values measured in each irradiation. Users must input the RDSRs to their program and compare output doses with reference doses. The authors performed 27 irradiations using two C-arms from different manufacturers. For each irradiation, the authors modified parameters that affect skin dose and measured it with an ionization chamber placed under a water phantom. The methodology was applied to validate the program SkinDose 2D. Results. Experimental measurements have an uncertainty of 13% (k=2). SkinDose 2D dose predictions differ from measurements in -9% to +8%, within experimental uncertainty. Conclusions. Varying different parameters that affect skin dose, this methodology allows for an initial validation of skin dose programs, characterizing them before any other additional measurement done by the user.

Assessment of individual external exposure doses based on environmental radiation in areas affected by the Fukushima Daiichi Nuclear Power Station accident

Assessing individual external exposure doses from ambient dose equivalents is valuable for predictive and retrospective purposes when personal dosimeters are impractical. This study developed a model to assess individual external exposure doses from ambient dose equivalents, considering daily life patterns (location and time spent in various places), and evaluated parameters associated with individual external exposure doses, such as the reduction effects of radiation due to buildings and vehicles. The model parameters were evaluated using the robust datasets of environmental radiation measured in areas affected by the Fukushima Daiichi Nuclear Power Station (FDNPS) accident. The effective dose estimated by the model was compared to 106 daily personal dose equivalents measured using personal dosimeters in the residents’ living environments near the FDNPS. The estimated effective dose well consists with the measured personal dose equivalents, particularly when considering natural radiation in indoor dose estimation. This model is adequate for radiation protection, enabling the predictive and retrospective estimation of individual external exposure doses using environmental radiation monitoring data.

Investigation on the impact of the spatial arrangement of individuals in a standing-type in-vivo monitoring system

An automated standing type Quick Scan Whole Body Monitor (QS-WBM) has been developed for the measurement of internal radioactive contamination due to high energy photon (HEP) emitters (Eϒ >200keV). Individuals are monitored while standing on a platform inside QS-WBM at specified reference position. Instances may occur where individuals deviate from their monitoring position, potentially leading to errors in the measurement of the body content. Positional inaccuracies are estimated in three potential scenarios: lateral displacement of the individual, movement perpendicular to the detector face, and forward bending of the torso. The Monte Carlo particle transport code FLUKA is used for estimation of efficiencies for selected radionuclides across various geometrical positions for adult male radiation workers. Approximately, 8% variation in calibration factors (CFs) is noted for lateral movements up to 15 cm from the centerline regardless of the energy, while perpendicular movements from reference position exhibit variations ranging from 14 to 60 %. This study helps in quantifying uncertainties in the estimation of body content and dose, arising from deviations in position of individuals in QS-WBM enclosure during monitoring.

CT surveillance for type 1 autoimmune pancreatitis: cumulative radiation dose and diagnostic performance for disease relapse.

Long-term follow-up is essential for type 1 autoimmune pancreatitis (AIP) patients due to high relapse rates. The cumulative radiation dose from repeated CT scans during follow-up should not be ignored. We aim to investigate the cumulative radiation dose in AIP patients undergoing CT surveillance and the diagnostic performance of CT in detecting disease relapse. The diagnostic performance of MRI from a secondary cohort during the same period was also investigated. This retrospective single-institutional study included 247 type 1 AIP patients with one or more follow-up CT scans, and 120 patients with MR follow-ups. Four metrics were utilized to report the radiation dose, including the volume computed tomography dose index, the dose length product, size-specific dose estimate and effective dose. The diagnostic performance for AIP relapse was assessed, taking the final clinical diagnosis in retrospect as the reference standard. With a median 2.3-year follow-up period, AIP patients followed up with CT exhibited a median cumulative radiation dose of 37.5 mSv. 11.3% of patients have accumulated doses exceeding 100 mSv. For the 169 patients followed over a year, 30.8% sustained an average annual radiation dose surpassing 20 mSv. The sensitivity/specificity/accuracy of CT for detecting abdominal organ relapse was 64.1%/99.6%/97.0%. For AIP patients followed up with MRI, the sensitivity for detecting disease relapse was 90.5%. Considering the accumulation of radiation dose in AIP patients and the insufficient sensitivity in detecting disease relapse with CT, safer and more sensitive imaging follow-up strategies should be explored. Question CT, as the primary imaging modality for autoimmune pancreatitis (AIP) follow-up, raises concerns regarding radiation exposure and lacks reported diagnostic performance in detecting AIP relapse. Findings CT in AIP follow-up causes significant cumulative radiation exposure and exhibits insufficient sensitivity in relapse detection. Clinical relevance Type 1 AIP necessitates long-term imaging follow-up, yet current guidelines lack consensus regarding the prioritization of CT or MRI for such follow-up. CT is widely used but has radiation concerns and limited sensitivity, calling for safer, efficient strategies.

HeadCTDosi: A python-based automated calculation of head water equivalent diameter and size specific dose estimate based on AAPM 220 report

HeadCTDosi: A python-based automated calculation of head water equivalent diameter and size specific dose estimate based on AAPM 220 report

Clinical diagnostic reference levels and image quality metrics for CT in oncology patients

Background: In CT, the volumetric CT dose index (CTDIvol), dose-length product (DLP) and patient’s size-specific dose estimates (SSDE) are used as diagnostic reference level (DRL) metrics.Objectives: To develop clinical local DRL values for CT chest-abdomen-pelvis (CAP) examinations using the CTDIvol, DLP and SSDE, and to determine the image quality achieved.Method: In total, 201 cancer patients were included in the study. The scanning parameters, dose metrics from the CT unit and participants’ body mass index (BMI) were documented. The local CT DRL values for CAP examinations were defined as the median and 75th percentiles of the dose distribution.Results: The local DRL values given in terms of median CTDIvol ranged between 8.4 mGy and 12.7 mGy for the different types of cancers. The median DLPs ranged from 848 to 1173.4 mGy.cm for the various cancers. Generally, the radiation dose was directly proportional to the BMI and number of scan phases. Significant differences were observed between the DRLs for the various size-related parameters, number of scan phases and BMI classifications. The image quality was clinically satisfactory.Conclusion: No baseline data for clinical DRL values were available for this medical oncology department. The achieved DRLs were similar to published size-specific DRLs. The image quality was maintained during CT imaging. Dose optimisation and image quality assessment should be implemented to ensure optimal scanning parameters for different cancers in CT CAP examinations.Contribution: The first size-specific local DRL values for CT CAP investigations carried out on oncology patients in South Africa have been established.

Pediatric contrast-enhanced chest CT on a photon-counting detector CT: radiation dose and image quality compared to energy-integrated detector CT.

Photon counting detector (PCD) CT benefits from reduced noise compared with conventional energy-integrating detector (EID) CT, which should translate to improved image quality and reduced radiation exposure for pediatric patients undergoing chest CT with IV contrast. To determine the differences in radiation exposure and image quality of PCD CT and EID CT in pediatric chest CT with intravenous (IV) contrast. In this institutional review board-approved retrospective observational study, 20 scan pairs (20 PCD CT; 20 EID CT) for children who underwent chest CT with IV contrast on both a PCD CT (Siemens NAEOTOM Alpha) and an EID CT (Siemens SOMATOM Definition Edge or Force) within 12months were reviewed independently by three pediatric radiologists for three subjective quality features on 5-point Likert scales: overall quality, small structure delineation, and motion artifact. Objective measures of image quality (image noise, signal-to-noise ratio, and contrast-to-noise ratio) were assessed by a single radiologist in several locations in the chest through region of interest measurement of Hounsfield units (HU) and standard deviation. Patient-related and radiation exposure parameters were collected for each scan and summarized with median and interquartile range (IQR). The Wilcoxon rank-sum test was utilized to compare groups. A P < 0.05 indicated statistical significance. Inter-observer agreement of subjective image quality metrics was analyzed using weighted kappa. Age (14.2years vs 13.8years, P= 0.15), height (P= 0.13), weight (P= 0.21), and BMI (P = 0.24) did not significantly differ between groups. There were 10 male and 3 female patients. Compared to EID CT, PCD CT showed lower radiation exposure parameters including volumetric CT dose index, 1.7mGy (IQR 1.1-2.4mGy) vs 3.8mGy (IQR 2.0-4.7mGy) (P< 0.01), and size-specific dose estimate, 2.6mGy (IQR 1.8-3.1mGy) vs 5.0mGy (IQR 3.3-6.2mGy) (P< 0.01). Objective image quality of lung parenchyma was improved on the PCD CT scanner, including image noise 119.5 HU (IQR 95.4-135.7 HU) vs 143.1 HU (IQR 125.4-169.8 HU) (P < 0.01), signal-to-noise ratio (SNR) -6.1 (IQR -8.4 to -4.8) vs -4.9 (IQR -5.6 to -3.8) (P= 0.01), and contrast-to-noise ratio -63.9 (-84.1 to -57.5) vs -60.5 (-76.3 to -52.5) (P = 0.01). Motion artifact was improved on the PCD CT scanner (P< 0.01). No significant differences in overall image quality or small structure delineation were identified (P= 0.06 and P= 0.31). PCD CT pediatric chest CT had significantly reduced radiation exposure, improved image quality, and reduced motion artifact compared with EID CT.

Direct measurement of indoor thoron and radon progeny and estimation of inhalation dose in three cities in Gabon: Comparison of the use of thoron typical and measured equilibrium factor values

This study focuses on public exposure to natural radioactivity caused by the inhalation of radon and thoron progeny in homes in Franceville, Moanda and Mounana in Gabon. The equilibrium factor (FTn) between thoron and its progeny was determined experimentally for a proper estimate of the effective dose. In order to assess internal exposure due to radon and thoron progeny, 150 passive radon-thoron discriminative detectors (RADUET) and thoron progeny monitors were deployed for about 3 months in the above-mentioned towns. The results of the measurements obtained showed that the average concentrations of thoron progeny (EETC) were 1.54 ± 0.08 Bq m−3, 3.05 ± 0.09 Bq m−3 and 1.84 ± 0.11 Bq m−3 in Franceville, Moanda and Mounana, respectively. The ranges of the measured thoron equilibrium factors were 0.004–0.710, 0.005–0.750, and 0.006–0.794 in Franceville, Moanda and Mounana, respectively. The arithmetic and geometric mean values were, respectively, 0.183 and 0.117 in Franceville, 0.184 and 0.122 in Moanda, and 0.221 and 0.140 in Mounana. The experimentally determined equilibrium factor (FTnexp) allowed us to compare the value of the experimentally determined effective dose with the theoretically determined one calculated using the equilibrium factor proposed by United Nation Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) 2000 report. FTnexp values were around 6–11 times greater than the UNSCEAR typical value. The ranges, arithmetic and geometric mean EERC values determined were 30.40–55.60 Bq m−3, 24.00 ± 0.90 Bq m−3 and 41.68 (1.00) in Franceville, 36.40–62.50 Bq m−3, 45.30 ± 0.70 Bq m−3 and 44.72 (1.00) in Moanda, and 35.00–90.00 Bq m−3, 50.00 ± 2.00 Bq m−3 and 48.50 (1.00) in Mounana. The mean values of the annual effective inhalation dose due to thoron progeny determined using FTnexp were 0.32 mSv (compared to 0.049 mSv), 0.63 mSv (compared to 0.103 mSv), and 0.39 mSv (compared to 0.055 mSv) in Franceville, Moanda and Mounana, respectively. The main conclusion of this study is that indirect estimations of thoron progeny concentrations considerably underestimate the estimation of the annual effective inhalation dose.