Journal of Radiation Research最新文献

The accelerator-based boron neutron capture therapy (BNCT) system has been approved for specific cases covered by health insurance, and clinical trials for new cases in Japan are currently being conducted on other systems. Owing to the progress of accelerator-based BNCT, the operation of medical physics must be rendered more efficient. A water phantom is used for the quality assurance (QA) of the BNCT beam output procedure; however, a solid phantom is preferred for routine QA because of its ease of use. Additionally, because water phantoms cannot be readily used in some facilities owing to structural problems, solid phantoms are preferred for unified measurements at different facilities to compare beam outputs. In this study, we perform irradiation tests using an acrylic phantom and verify that an acrylic phantom can be used for QA. The distribution of thermal neutron flux and gamma-ray dose rate inside the acrylic phantom are evaluated through experiments and simulations. The results indicate that the acrylic phantom is suitable for routine QA and for comparing beam outputs among different systems. In the future, the same irradiation tests will be conducted at other facilities.

Medulloblastomas are one of the most common malignant cancers of the central nervous system in children. Proton beam therapy (PBT) is expected to provide equivalent tumor control to photon therapy while reducing the various adverse events caused by irradiation. Few studies have considered the cost-effectiveness of PBT for pediatric medulloblastoma, considering the multiple adverse effects and reflecting on the latest treatment advancements. A cost-utility analysis of PBT for pediatric medulloblastoma was conducted in a Japanese setting and compared to conventional photon therapy. The analysis was conducted from the public healthcare payer's perspective, and direct costs for the treatment of radiation therapy and radiation-induced adverse events were included. A Markov model was used, and the health states of secondary cancer, hypothyroidism and hearing loss were defined as adverse events. The time horizon was the lifetime. Incremental cost-effectiveness ratio (ICER) was used as a measurement of cost-effectiveness, with quality-adjusted life years (QALYs) used as an outcome. The costs were estimated from the national fee schedule, and the utility and transition probabilities were estimated from published literature. PBT incurred an additional 1387116 Japanese yen (JPY) and 1.56 QALYs to the comparator. The ICER was JPY 887053/QALY, indicating that PBT was cost-effective, based on the reference value of JPY 5 million/QALY used in the Japanese cost-effectiveness analysis. Deterministic sensitivity analysis showed that the ICER ranged from JPY 284782/QALY to JPY 1918603/QALY as a result of deterministic sensitivity analysis, and probabilistic sensitivity analysis showed that PBT was cost-effective, with a probability of 91.7%.

The purpose of this study was to evaluate the feasibility of treatment plans for prostate cancer with magnetic resonance (MR)-guided online adaptive radiotherapy, which are generated using deformable image registration (DIR)-created contours of the targets and organs. Totally, 150 fractions from 30 prostate cancer patients implanted with a hydrogel spacer and treated with the MR-Linac were studied. Reference treatment plans that satisfied all institutional dose constraints were initially created on planning MRI. The adaptive treatment plans were created on daily MRI based on the reference plan using the DIR-created contours, ensuring all dose constraints were met. Subsequently, a clinician manually created reference contours for each daily MRI. Finally, the dose volume histogram indices of the plan generated with DIR-created contours were re-evaluated with clinician created contours. The evaluated contours included the bladder wall, rectum wall, sigmoid, small bowel and planning target volume (PTV) for dose prescription. The PTV for dose prescription met the dose constraints in all fractions. The bladder and rectum walls met the dose constraint of maximum dose (D0.03 cc) in all fractions. Five patients failed to meet the sigmoid and small bowel dose constraints, with the largest deviation being 13.3% exceedance at D2 cc in the small bowel added 3 mm margin. This study suggests that most treatment plans created without modifying the DIR-created contours are clinically viable. However, dislodgements of the small bowel and sigmoid may exceed the extent of DIR propagation from the reference plan contours, and it is recommended that these contours be verified.

We aimed to clarify whether prophylactic cranial irradiation (PCI) is associated with improved outcomes in limited-stage small-cell lung cancer (LS-SCLC) in the current era of magnetic resonance imaging (MRI). Data from patients with LS-SCLC who achieved a complete response to definitive chemoradiotherapy (CRT) at two medical centers were retrospectively reviewed. Propensity score-matching was performed in a 2:1 ratio to balance the baseline characteristics of the no-PCI and PCI groups. The endpoints were the incidence of brain metastasis (BM), neurological causes of death and overall survival (OS). Overall, 80% patients underwent head MRI during the initial staging and 75 patients (no-PCI, n = 50; PCI, n = 25) were matched. Their baseline characteristics were generally well-balanced except for age; patients in the no-PCI group tended to be older. The median follow-up period was 29 months. Although the incidence of BMs tended to be higher in the no-PCI group (1-year BM occurrence: 26% vs 17%, P = 0.22), the incidence of multiple BMs (defined as >4 metastases) was similar between groups (1-year multiple BMs occurrence: 8% vs 9%, P = 0.65). The 2-year neurological causes of death and OS rate did not significantly differ between the groups (6% and 9%; P = 0.85; and 70% and 79%; P = 0.36, respectively). The 1-year occurrence of multiple BMs did not increase, even without PCI, when modern imaging modalities were integrated into the initial diagnosis, suggesting that PCI could be omitted after CRT, if MRI was incorporated into the initial diagnosis and follow-up.

Our previous study demonstrated that the linear quadratic model appeared to be not well-suited for high dose per fraction due to an observed increase in α/β ratio as the dose per fraction increased. To further validate this conclusion, we draw the cell survival curve to calculate the α/β ratio by the clone formation experiment and then convert the fractionated radiation dose into an equivalent single hypofractionated radiation dose comparing with that on the survival curve. Western Blot and laser confocal immunofluorescence were used to detect the expression of γ-H2AX and RAD51 after different fractionated modes of radiation. We constructed a murine xenograft model, and changes in transplanted tumor volume were used to evaluate the biological effects after different fractionated radiation. The results demonstrated that when fractionated radiation dose was converted into equivalent single hypofractionated radiation dose, the effectiveness of hypofractionated radiation was overestimated. If a larger α/β ratio was used, the discrepancy tended to become smaller. γ-H2AX was higher in 24 h after a single high dose radiation than the continuous expression of the DNA repair marker RAD51. This implies more irreparable damage in a single high dose radiation compared with fractionated radiation. In the murine xenograft model, the effectiveness of hypofractionated radiation was also overestimated, and additional fractions of irradiation may be required. The conclusion is that after single hypofractionated radiation, the irreparable damage in cells increased (α value increased) and some repairable sublethal damage (β value) was converted into irreparable damage (α value). When α value increased and β value decreased, the ratio increased.

Brachytherapy (BT), especially in high dose rate (HDR), has become increasingly complex owing to the use of image-guided techniques and the introduction of advanced applicators. Consequently, radiotherapy technologists and medical physicists (RTMPs) require substantial training to enhance their knowledge and technical skills in image-guided brachytherapy. However, the current status of the RTMP workload, individual abilities and quality control (QC) of BT units in Japan remains unclear. To address this issue, we conducted a questionnaire survey from June to August 2022 in all 837 radiation treatment facilities in Japan involving RTMPs. This survey focused on gynecological cancers treated with HDR-BT (GY-HDR) and permanent prostate implantation using low-dose-rate BT (PR-LDR). The responses revealed that the average working time in the overall process for HDR varied: 120 min for intracavitary BT and 180 min for intracavitary BT combined with interstitial BT. The QC implementation rate, in accordance with domestic guidelines, was 65% for GY-HDR and 44% for PR-LDR, which was lower than the 69% observed for external beam radiation therapy (EBRT). Additionally, the implementation rate during regular working hours was low. Even among RTMP working in facilities performing BT, the proportion of those able to perform QC for BT units was ~30% for GY-HDR and <20% for PR-LDR, significantly lower than the 80% achieved for EBRT. This study highlights the vulnerabilities of Japan's BT unit QC implementation structure. Addressing these issues requires appropriate training of the RTMP staff to safely perform BT tasks and improvements in practical education and training systems.

FLASH radiotherapy is an emerging technique in radiation oncology that may improve clinical outcomes by reducing normal tissue toxicities. The physical radiation characteristics needed to induce the radiobiological benefits of FLASH are still an active area of investigation. To determine the dose rate, range of doses and delivery time structure necessary to trigger the FLASH effect, Drosophila melanogaster were exposed to ultrahigh dose rate (UHDR) or conventional radiotherapy dose rate (CONV) 120-kVp X-rays. A conventional X-ray tube outfitted with a shutter system was used to deliver 17- to 44-Gy doses to third-instar D. melanogaster larvae at both UHDR (210 Gy/s) and CONV (0.2-0.4 Gy/s) dose rates. The larvae were then tracked through development to adulthood and scored for eclosion and lifespan. Larvae exposed to UHDR eclosed at higher rates and had longer median survival as adults compared to those treated with CONV at the same doses. Eclosion rates at 24 Gy were 68% higher for the UHDR group (P < 0.05). Median survival from 22 Gy was >22 days for UHDR and 17 days for CONV (P < 0.01). Two normal tissue-sparing effects were observed for D. melanogaster irradiated with UHDR 120-kVp X-rays. The effects appeared only at intermediate doses and may be useful in establishing the dose range over which the benefits of FLASH can be obtained. This work also demonstrates the usefulness of a high-throughput fruit fly model and a low-cost X-ray tube system for radiobiological FLASH research.

Stereotactic radiosurgery (SRS) using the single-isocenter-multiple-target (SIMT) technique by volumetric modulated arc therapy is increasingly popular for treating multiple brain metastases. However, the complex nature of SIMT SRS necessitates rigorous patient-specific quality assurance (PSQA). This study presents a multi-institutional dosimetric commissioning of a high-resolution complementary metal oxide semiconductor (CMOS) 2D detector array, the myQA SRS device for SIMT SRS PSQA. Basic dosimetric properties such as dose-rate, field-size, energy and angular dependencies were characterized for the CMOS detectors. Additionally, gamma index analyses were performed between the measured dose and the films for nine simulated and clinical plans. The results showed that the CMOS detector was dose-rate, field-size, energy and beam-angle dependent. Specific to SIMT SRS, angular dependence on gantry rotations was invariant to couch rotations but was sensitive to off-isocenter distances. With appropriate dose calibration and angular corrections, myQA SRS showed a high dosimetric correlation with films. The average gamma index pass rates were 99.9 ± 0.03% and 99.2 ± 1.1% at 3%/2 mm/10%thr(global) and 1 mm/1%/10%thr(local) criteria, respectively. The average dose difference between myQA SRS and films was 0.4 ± 1.3%. In conclusion, the CMOS 2D detector array has demonstrated its potential as a reliable tool for PSQA for SIMT SRS. The excellent dosimetric agreement with the films was consistent in multiple institutions, further validating the dosimetric accuracy and reproducibility. It provides a timely alternative to film dosimetry for commissioning and quality assurance.

This study aimed to visualize the current situation and trends in radiation therapy in Japan using open data from the Japanese National Database of Health Insurance Claims and Specific Health Checkups (NDB). We downloaded the NDB open data from the website of Japan's Ministry of Health, Labor and Welfare and used Python libraries to analyze the receipt data related to radiation therapy from fiscal year 2014 to 2022. The number of radiation therapy plans peaked in 2019, temporarily declined and subsequently showed a gradual increase. Conversely, the total points associated with radiation therapy have consistently increased without any decline. The use of high-precision radiation therapies such as intensity-modulated radiation therapy (IMRT) has increased over time. Significant regional differences exist, with the Chubu and Kyushu regions showing higher total points and receipts per certified radiation oncologist. A correlation was observed between the number of IMRT plans per population and the number of certified radiation oncologists. Males exhibited a sharp peak in their early 70s, while females demonstrated a mild peak from their 40s to 80s. In recent years, the points for males in their early 70s have rapidly increased. We used the NDB open data to illustrate the current situation and trends in radiation therapy in Japan, highlighting reduced costs and workloads. This study underscored the regional differences in radiation therapy and emphasized the need to discuss strategies for meeting future demand.