Purpose: To evaluate the dose calculation accuracy in areas exposed to air on a radiotherapy treatment planning system using a phantom model simulating early-stage glottic cancer. Methods: An air gap was placed between water-equivalent phantoms, and 6 MV X-rays were delivered at 200 MU. The absorbed dose in the depth direction was measured using Gafchromic film. These measurements were compared with calculations from Pinnacle3 (collapsed cone convolution: CCC) and RayStation (photon Monte Carlo: pMC, CCC). Results: The difference between the measured film values after passing through the air gap and the calculated values of each algorithm was up to 14.4% with RayStation CCC and −3.8% with RayStation pMC. Conclusion: The pMC method offers higher accuracy in calculating surface dose at air–tissue boundaries than the CCC method, which overestimates the absorbed dose at the surface. When the dose around heterogeneous regions involving air is clinically very important, using RayStation pMC allows for more accurate dose calculations.

Purpose: This study aimed to evaluate the usefulness of variable helical pitch scanning (vHP) on the uniformity of contrast enhancement in wide-range computed tomography angiography (CTA) from the chest to the lower extremities using contrast media administered at 400 mgI/kg over 20 seconds. Methods: Using the double-level test bolus injection (DLTI) method to determine the contrast arrival time, CTA scans were performed with a fixed-HP method (n=20) and a variable-HP method using vHP (n=20). The CT numbers at five major arterial regions were compared, and a visual assessment was also conducted. Results: Compared with the fixed-HP method, the variable-HP method significantly increased the CT number in the abdominal aorta and femoral arteries (p<0.05) and improved the uniformity of contrast enhancement along the body axis. The visual assessment also showed significantly higher ratings for the variable-HP method (p<0.05). Conclusion: The protocol combining DLTI and vHP techniques is useful for achieving more uniform contrast enhancement from the chest to lower extremities in CTA while reducing the contrast medium volume, and is expected to improve diagnostic performance.

Purpose: The aim of this study was to quantitatively evaluate the impact of gantry, collimator, and couch rotational errors in a linear accelerator on the irradiation accuracy of off-isocenter targets, and to assess the validity of the rotational error tolerance (±1.0°) specified in American Association of Physicists in Medicine TG142. Methods: Using an Elekta linear accelerator (Elekta, Stockholm, Sweden) and the MultiMet-WL QA phantom (Sun Nuclear, Melbourne, FL, USA), an off-isocenter Winston–Lutz test was performed on six targets. In addition to baseline measurements, six conditions were evaluated by intentionally introducing rotational errors of +0.5° and +1.0° in the collimator, gantry, and couch. The vector distance (S value) between the field center and the target center, as well as positional deviations in each direction (gantry-target: GT, left-right: LR, anterior-posterior: AP), were analyzed. Results: Targets located farther from the isocenter exhibited more significant positional deviations. The collimator rotation had the greatest impact; at 7 cm from the isocenter, even a 0.5° error resulted in a maximum S value of 1.24 mm. Couch rotation had the next largest effect, while gantry rotation had relatively smaller effects, likely because most targets were located near the gantry’s rotational axis. The rotational errors mainly caused geometric deviations with direction-dependent positional shifts. Conclusion: The effects of the collimator and couch were substantial, with positional deviations exceeding 1 mm even for a 0.5° rotation error. The influence of the gantry was relatively small and dependent on the target configuration. For irradiation of off-axis targets, the TG142 tolerance of ±1.0° should be regarded as a minimum standard that must be strictly observed regardless of the type of linear accelerator. However, depending on the target arrangement, clinically adequate margins may not be ensured. These findings suggest the necessity of applying stricter criteria according to target configuration and emphasize the importance of regular quality assurance.

The purpose of this study was to evaluate the intra-fractional motion (IFM) in stereotactic body radiation therapy (SBRT) for metastatic spinal tumors according to different irradiation site groups. We analyzed IFM during SBRT in 31 patients (32 lesions) treated at our institution from January 2022 to April 2023. IFM was evaluated in 3 groups according to the targeted spinal regions as follows: the cervical and upper thoracic, the lower thoracic, and the lumbar-sacral (L–S). IFM was defined as the displacement measured by acquired with the orthogonal kV–kV imaging system (ExacTrac; BrainLab, Munich, Germany) before and after irradiation. Correlations between IFM and treatment time were examined. The planning target volume (PTV) was determined by adding a 2 mm margin to the clinical target volume. The results showed that IFM for three groups was within 2 mm/2° for more than 95% of all fractions. There was no strong correlation between IFM and treatment time. The correlation coefficient between IFM and treatment time was up to 0.43 in the anterior–posterior direction of the L–S group. In conclusion, the IFM of SBRT for spinal metastases at our institution was within 2 mm for more than 95% of all fractions, which was encompassed by the PTV.

Purpose: To investigate the optimal positioning for low-birth-weight infants using a vacuum fixation device, considering the most suitable position for each manufacturer’s coil. Methods: Image data of low-birth-weight infants scanned at the institution were measured to assess their physical characteristics. Uniformity was evaluated by imaging a common phantom under identical imaging conditions using the head coils provided by GE Healthcare (Milwaukee, WI, USA), Siemens Healthineers (Erlangen, Germany), and Philips Healthcare (Best, the Netherlands). Results: The physical characteristics of low-birth-weight infants allowed them to fit entirely within all manufacturers’ coils. Uniformity varied depending on the coil type and the position within the coil: uniformity was highest in the deeper position for the GE 8-channel coil, in the central position for the Siemens 20-channel coil, in the deeper position for the Philips 32-channel coil, and in the central position for the Philips 20-channel coil. Conclusion: When using a vacuum fixation device in low-birth-weight infants, optimal positioning was achieved by adjusting for the thickness of the fixation device and placing the infant at the position within the coil where imaging uniformity was highest.

Purpose: This study aimed to evaluate radiation exposure during catheter ablation procedures, focusing on the air kerma at the patient entrance reference point (K_a,r) and air kerma area product (P_KA), which were newly introduced in the 2020 Diagnostic Reference Levels (DRLs). Additionally, we sought to clarify differences in radiation doses among different ablation techniques. Methods: A nationwide survey was conducted across medical institutions in Japan between December 2021 and March 2022. Data were collected retrospectively for procedures performed from June 2019 to May 2021. Information was gathered on fluoroscopic protocols (reference fluoroscopy dose rate and cine dose rate) and radiation exposure parameters, including K_a,r, P_KA, fluoroscopy time, number of cine runs, and number of cine frames, categorized by three ablation techniques: non-pulmonary vein isolation (non-PVI), catheter PVI, and balloon PVI. Results: The median K_a,r values were 128 mGy for non-PVI, 170 mGy for catheter-based PVI, and 228 mGy for balloon PVI. Significant differences (p<0.05) were observed among the three techniques in terms of P_KA, fluoroscopy time, number of cine runs, and number of cine frames. Conclusion: A downward trend in radiation dose was observed in catheter ablation procedures. However, radiation doses varied among techniques, with balloon PVI demonstrating higher values compared to other methods. These findings underscore the importance of continuous dose monitoring and may contribute valuable data for future DRL revisions.