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.

Purpose: To investigate the dosimetric characteristics of intracavitary/interstitial brachytherapy (IC/ISBT) plans created via the hybrid inverse planning optimization (HIPO) algorithm with the dwell time Lock function.

Materials and methods: Sixteen patients with locally advanced cervical cancer treated with high-dose-rate IC/ISBT were evaluated. Based on the clinical plan data, five plans were retrospectively created: Manchester-based HIPO for needles, HIPO for all applicators, HIPO for needles after HIPO for tandem/ovoid, HIPO for ovoid after HIPO for tandem/needle, and HIPO for ovoid/needle after HIPO for tandem. The target coverage, organs at risk (OARs) doses, therapeutic ratios, and the dwell time contributions of the needles were analyzed to evaluate the plan quality. Dice similarity coefficients (DSCs) between clinical plan and each created plan were calculated to evaluate the similarity of the shape of the dose distribution.

Results: All plans created using HIPO had a sufficient target coverage, while the OAR dose for the Manchester-based HIPO plans was considerably higher than the other plans. The plan with HIPO for all applicators and with HIPO for the ovoid applicator after HIPO for tandem/needles had comparable or superior therapeutic ratios than those of the clinical plan while the dwell time contributions of the needle were much larger. For DSCs, an intermediate to low correlation was observed between the clinical plan and all HIPO plans.

Conclusions: The HIPO algorithm could create high-quality IC/ISBT plans, although the dosimetric consequences were affected by the locking function.

Purpose: The purpose of this study was to validate the accuracy of a method for determining the iodine contrast dose using effective diameter (D_eff) when performing dynamic computed tomography (CT) scans of the upper abdomen in patients with unknown body weight (BW).

Methods: D_eff was measured at the heart, at the right diaphragm upper edge, and at the right pulmonary rib diaphragm levels in the localizer radiograph and axial images. Correlation coefficients between D_eff and BW were determined for each cross section.

Results: D_{eff_axial} and BW showed the highest correlation at the right diaphragm upper edge level in men (r_S = 0.862) and at the right pulmonary rib diaphragm level in women (r_S = 0.890).

Conclusions: The BW estimated from D_eff showed a strong correlation with measured BW and may serve as a practical alternative in cases where BW is unknown.

In internal target volume (ITV)-based treatment planning, respiratory-gated four-dimensional computed tomography (4D-CT) is used to visualize the respiratory motions of lung tumors. However, in cases of irregular breathing, conventional 4D-CT cannot be synchronized with patient-specific respiratory waveforms, which poses challenges to obtaining images that accurately represent the ITV of the tumor. To address this challenge, we propose "simulated respiratory-gated 4D-CT" synchronized with the simulated waveform. This study aimed to assess the precision of ITV delineation using simulated respiratory-gated 4D-CT in patients with irregular breathing. A respiratory motion phantom was employed by inserting a simulated tumor and assessing the method under sinusoidal and irregular breathing conditions. Irregular respiratory waveforms of 20 patients were used to simulate irregular breathing. The phantom was imaged using conventional 4D-CT, slow-scan CT, and our method. For conventional 4D-CT and our method, the average and maximum intensity projections (MIP) were obtained via postprocessing. ITVs corresponding to each respiratory motion were manually contoured. Furthermore, the Dice similarity coefficient (DSC) was computed based on the ITV of conventional 4D-CT. No significant disparity was found between the ITVs obtained using our method and those obtained using conventional 4D-CT under sinusoidal motion. The DSC values of the ITVs derived from our method using MIP were the highest. In the assessment of the irregular respiratory waveforms, the ITVs obtained via MIP using our method closely approximated the ideal ITV in 20 patients. These findings demonstrate that our method can enhance the accuracy of ITV delineation in lung tumors during irregular breathing episodes.