Radiological Physics and Technology最新文献

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.

The use of radioprotective glasses alone may not reduce radiation sufficiently to protect the eyes of endoscopists performing endoscopic retrograde cholangiopancreatography (ERCP). In this study, we aimed to develop a radioprotective side shield that could be attached to radioprotective glasses. Air kerma was measured at the lens surface of an endoscopist phantom using optically stimulated luminescence dosimeters in an arrangement that simulated ERCP. The protective effect of the radioprotective side shield was evaluated by changing three factors: the number of sheets to be layered from 1 to 5, the front-side length of the sheet from 6 to 10 cm, and the rear-side length of the sheet from 5 to 7 cm. By increasing the front length of the sheets to 8 cm, their rear length to 6 cm, and increasing the number of sheets to three with a lead equivalent of 0.14 ± 0.02 mmPb, the air kerma on the ocular surface could be reduced considerably; hence, these changes were implemented. This achieved a dose reduction of 48.2-87.3% compared with the use of radioprotective glasses alone, especially when the endoscopist phantom was rotated 60° and 75° from the direction directly opposite to that of the patient phantom. The results suggest that radioprotective side shields can reduce radiation exposure in the eyes of endoscopists by < 0.03 mGy in 10-min fluoroscopy under most conditions during ERCP.

Accurate lateral knee radiographs are essential for assessing pathology and planning surgery. However, achieving adequate femoral condyle overlap is technically challenging because of individual variations in lower limb alignment. We analyzed the alignment-dependent bone morphology and proposed practical X-ray tube angles to optimize lateral imaging. Full-length lower limb radiographs of 212 normal and 191 knees with osteoarthritis (KOA) were examined. The lateral distal femoral angle (LDFA) and medial proximal tibial angle were measured to classify the alignment into varus, neutral, and valgus types. The LDFA increased with varus alignment in both the normal (89.1°, 88.0°, and 85.2°) and KOA knees (90.2°, 88.0°, and 85.0°). The joint line orientation consistently exhibited an apex-distal pattern. The distal femoral tangent angle (θ = 90° - LDFA) ranged from - 0.2° to 5.0°, providing reference targets for X-ray tube inclination. This alignment-based approach improved imaging reproducibility and diagnostic accuracy in both normal and KOA knees.

The gamma-ray dose rate distribution at the Kindai University Reactor (UTR-KINKI) was measured using the thermoluminescent (TL) properties of beryllium oxide (BeO) ceramic plates. The reactor, operating at an extremely low thermal power of 1 W, is widely used for nuclear research, including radiation biology and detector development. In neutron-gamma mixed fields, determining the gamma-ray dose rate accurately is technically challenging due to the neutron sensitivity of conventional dosimeters. In this study, low-Na BeO ceramic thermoluminescence dosimeters (TLDs) were employed to selectively measure gamma-ray dose rates in the irradiation hole of UTR-KINKI, without the need for neutron correction. A comparative assessment was conducted using Na-doped BeO powder TLDs, and thermal neutron flux measurements were performed using a Li-glass scintillator. The results demonstrated that the height-dependent trend of the gamma-ray dose rate distribution was consistent with previous measurements obtained via paired ionization chambers. However, the absolute values of the gamma-ray dose rates measured with the BeO ceramic TLDs were approximately 10-30% higher than those determined by the paired ionization chamber. This discrepancy is likely due to neutron sensitivity considerations in previous studies. The gamma-ray dose rate at the reactor center was evaluated as approximately 24 cGy h^-1. This study highlights the applicability of BeO ceramic TLDs for gamma-ray dosimetry in mixed radiation fields, offering a neutron-insensitive alternative for precise dose measurements in reactor environments.