Radiological Physics and Technology最新文献

The global increase in computed tomography (CT) use, highlighted by a 40% growth in South Korea over the past decade, has made CT a significant source of medical radiation exposure, emphasizing the need for accurate effective dose (ED) estimation. This study aimed to develop population-specific effective dose conversion factors (k-factors) for brain CT examinations across the range of tube voltages used in Korean hospitals. Clinical dose parameters were obtained from the Korean National CT Dose Index Registry (KNCTDIR), which compiles large-scale dose-length product (DLP) data from 45 hospitals nationwide. The mean, maximum, and minimum kVp and DLP values were selected to represent typical clinical variations. Monte Carlo simulations were performed using GATE version 10.0b8 with Korean-sized XCAT phantoms for adult and pediatric groups. Organ and effective doses were calculated following ICRP 103 tissue-weighting factors, and k-factors were derived for each age, sex, and voltage condition. The results showed consistent k-factors across the evaluated voltage range, with only minimal sex-related differences. Infants had the highest coefficients (0.0029 mSv/mGy·cm), while pediatric k-factors were lower and remained relatively stable from ages 2 to 15 years. Comparisons with previous Korean and international studies revealed notable quantitative differences, emphasizing the need for updated, population-specific coefficients. The revised k-factors facilitate practical and consistent effective-dose estimation in Korean brain CT procedures.

Dosimetry using SPECT/CT images enables personalized medicine by estimating absorbed doses and optimizing therapy. Differences in organ contouring and calculation algorithms contribute to inter-institutional variability, emphasizing the need for standardization. The present study aimed to investigate factors contributing to inter-institutional variability in kidney dosimetry in Japan. We analyzed four time points in SPECT/CT images of one male and one female patient each from the ¹⁷⁷Lu SNMMI Dosimetry Challenge. Kidney volumes and absorbed doses were calculated at 10 Japanese institutes using their preferred organ-based (OLINDA 2.2, IDAC DOSE 2.1) and voxel-based (Voxel Dosimetry, RT-PHITS, MIM SurePlan MRT, OpenDose3D) software. Reference volumes of interest (VOI) files were distributed to assess the effect of contouring differences on kidney volumes and absorbed doses. Manual VOI contouring revealed substantial inter-institutional variability in kidney volumes, with coefficients of variation (%CVs) up to 16.9%. The reference VOIs reduced volume variability to ≤ 7.4%. Compared to manual VOIs, reference VOIs showed slightly increased doses in both patients with slightly reduced inter-institutional variability. The absorbed doses were generally higher in voxel- than organ-based dosimetry. The %CVs of the right and left kidneys in female patient decreased from 31.36% to 6.26% and 41.28%-3.97%, respectively. Variability in Kidney volume and absorbed doses significantly varied among Japanese institutes. Reference VOIs reduced volume variability but could not fully control dose differences. Voxel-based dosimetry can mitigate inter-institutional variability independent of contouring. Our findings emphasize the importance of algorithm standardization for reliable ¹⁷⁷Lu-DOTATATE kidney dosimetry in Japan.

This study aimed to evaluate discrepancies between planned, delivered and adapted doses to target and organs at risk (OARs) during bladder cancer radiotherapy, using deformable image registration from CT to CBCT in view of better treatment personalization. Twenty patients with a total of 165 CBCT images were analysed. Intensity modulated techniques (IMRT and VMAT) were simulated in the Monaco planning system. The initial plans were adapted to each CBCT using the Adapt to shape (ATS) function. A reduction in PTV66 and CTV66 coverage was observed upon calculation of treatment dose on CBCTcalc in comparison with plans on CT. The PTV66 coverage was 86.7% IMRT and 86.4% VMAT, respectively. Meanwhile, the optimized plans on CBCTopt provided PTV66 coverage of 97.1% IMRT and 96.4% VMAT, which was similar to the initial planning on CT (97.4% IMRT and 96.6% VMAT). Furthermore, CTV66 showed a coverage of 94.2% IMRT and 94.0% VMAT on CBCTcalc, in comparison to the values on CT (99.8% IMRT and 99.9% VMAT) and the values on CBCTopt (99.8% IMRT and 99.8% VMAT). For OARs, the rectum, bowel bag, and sigmoid exhibited higher values on CBCTcalc than on CT planning and CBCTopt. This study demonstrates that CBCT- guided adaptive radiotherapy enhances treatment precision and personalization in bladder cancer, improving target coverage and reducing radiation exposure to healthy tissues. Next to highlighting the importance of personalizing bladder cancer radiotherapy, the study substantiates that daily reoptimization with ATS constitutes an efficacious strategy in centers with limited resources.

This study aimed to develop a deep learning-based method for automatic segmentation of the pharyngeal area (PA) and measurement of the pharyngeal contraction ratio (PCR) during deglutition using cine magnetic resonance imaging (MRI). The proposed algorithm combines PA region extraction by a 2D U-Net with automatic calculation of PA and PCR. Segmentation performance was evaluated using the Dice coefficient (DC), and the PCR measured by the model ([Formula: see text]) was compared with that obtained manually ([Formula: see text]) using correlation and Bland-Altman analyses. Cine MRI data of 20 healthy adults (10 men, 10 women; age 22-29 years) were analyzed. The average DC in the test cases was 0.890 ± 0.025, and the PA of the model correlated well with the manual reference (r = 0.70-0.97). The mean [Formula: see text] was 0.105 ± 0.035, consistent with values reported in videofluoroscopic swallowing studies. These results demonstrate the technical feasibility of automatic PCR measurement from cine MRI using deep learning.

The goal of this study was to assess radiation doses to the eyes of seated patients and medical staff during a videofluoroscopic swallowing study (VFSS), considering the effects of lead-equivalent glasses and the height of the medical staff. Entrance surface air kerma (ESAK) at eye level was measured using nanoDot dosimeters on anthropomorphic phantoms representing medical staff with heights of 150, 165, and 180 cm. ESAK measurements were performed with and without 0.5-0.6 mm lead-equivalent glasses. During a 10-minute fluoroscopy procedure, the mean ESAK at patient's eyes without lead-equivalent glasses was higher in the anteroposterior (AP) position (36.5 mGy) than in the lateral position (14.5 mGy). The corresponding ESAK at medical staff's eyes was notably higher in the 150-cm phantom (0.097 mGy), with an increase of 77.1% compared with that in the 165-cm phantom (0.043 mGy) and 87.4% compared with that in the 180-cm phantom (0.038 mGy). The radioprotective efficiency of lead-equivalent glasses in patients in the anteroposterior position was 92.0-93.4%, which was higher than that in the lateral position (15.8-83.2%). Radiation doses to the eyes were highest for shorter medical staff, highlighting the importance of protective measures, especially for those with shorter stature. The radioprotective efficiency of lead-equivalent glasses was found to be lower in the lateral position, underscoring the need for careful consideration of glasses design.

To assess the reproducibility of native T1 value measurements across different myocardial slice positions and cardiac phases using a 1.5T magnetic resonance (MR) system. Twenty-seven healthy male volunteers (mean age 31.2 ± 4.8 years) underwent native T1 mapping on a 1.5T MR scanner (Ingenia, Philips) using a modified look-locker inversion recovery (MOLLI) 5-(3)-3 sequence. Short-axis images were acquired at the basal, mid, and apical levels of the left ventricle during both diastolic and systolic phases. Each acquisition was repeated twice. Native T1 values were measured using semi-automated region of interest (ROI) placement with Cvi42 software. Reproducibility was evaluated using Bland-Altman analysis. Native T1 values were 982.1 ± 27.9 ms (base), 988.3 ± 21.3 ms (mid), and 993.8 ± 49.2 ms (apex) during diastole, and 981.1 ± 35.1 ms (base), 989.1 ± 24.3 ms (mid), and 984.4 ± 33.3 ms (apex) during systole. No significant differences were observed between diastolic and systolic phases or across slice positions. Bland-Altman analysis revealed the narrowest 95% limits of agreement for mid-ventricular slices in systole (- 24.8 to 22.7 ms) and the widest for apical slices in diastole (- 48.1 to 56.2 ms). Reproducibility was consistently superior during systole compared to diastole. Native myocardial T1 values at 1.5T demonstrated reproducibility across both cardiac phases and slice positions in healthy subjects. However, systolic imaging provided narrower limits of agreement, particularly at the apex. Therefore, imaging in systole is recommended for assessing apical T1 values.