Journal of Radiation Research最新文献

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.

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.

This study aimed to identify the required capabilities and workload of medical staff in accelerator-based boron neutron capture therapy (BNCT). From August to September 2022, a questionnaire related to the capabilities and workload in the accelerator-based BNCT was administered to 12 physicians, 7 medical physicists and 7 radiological technologists engaged in BNCT and 6 other medical physicists who were not engaged in BNCT to compare the results acquired by those engaged in BNCT. Only 6-21% of patients referred for BNCT received it. Furthermore, 30-75% of patients who received BNCT were treated at facilities located within their local district. The median required workload per treatment was 55 h. Considering additional workloads for ineligible patients, the required workload reached ~1.2 times longer than those for only eligible patients' treatment. With respect to capabilities, discrepancies were observed in treatment planning, quality assurance and quality control, and commissioning between medical physicists and radiological technologists. Furthermore, the specialized skills required by medical physicists are impossible to acquire from the experience of conventional radiotherapies as physicians engaged in BNCT were specialized not only in radiation oncology, but also in other fields. This study indicated the required workload and staff capabilities for conducting accelerator-based BNCT considering actual clinical conditions. The workload required for BNCT depends on the occupation. It is necessary to establish an educational program and certification system for the skills required to safely and effectively provide BNCT to patients.

This study aimed to clarify the dosimetric impact of calibration beam quality for calibration coefficients of the absorbed dose to water for an ionization chamber in an on-site dosimetry audit. Institution-measured doses of 200 photon and 184 electron beams were compared with the measured dose using one year data before and after the calibration of the ionization chamber used. For photon and electron reference dosimetry, the agreements of the institution-measured dose against two measured doses in this audit were evaluated using the calibration coefficients determined using 60Co (${N}_{D,mathrm{w},{}^{60}mathrm{Co}}$) and linear accelerator (linac) (${N}_{D,mathrm{w},Q}$) beams. For electron reference dosimetry, the agreement of two institution-measured doses against the measured dose was evaluated using${N}_{D,mathrm{w},Q}$. Institution-measured doses were evaluated using direct- and cross-calibration coefficients. For photon reference dosimetry, the mean differences and standard deviation (SD) of institution-measured dose against the measured dose using ${N}_{D,mathrm{w},{}^{60}mathrm{Co}}$ and ${N}_{D,mathrm{w},Q}$ were -0.1% ± 0.4% and -0.3% ± 0.4%, respectively. For electron reference dosimetry, the mean differences and SD of institution-measured dose using the direct-calibration coefficient against the measured dose using ${N}_{D,mathrm{w},{}^{60}mathrm{Co}}$ and ${N}_{D,mathrm{w},Q}$ were 1.3% ± 0.8% and 0.8% ± 0.8%, respectively. Further, the mean differences and SD of institution-measured dose using the cross-calibration coefficient against the measured dose using ${N}_{D,mathrm{w},Q}$ were -0.1% ± 0.6%. For photon beams, the dosimetric impact of introducing calibration coefficients determined using linac beams was small. For electron beams, it was larger, and the measured dose using ${N}_{D,mathrm{w},Q}$ was most consistent with the institution-measured dose, which was evaluated using a cross-calibration coefficient.

Ionizing radiation promotes mammary carcinogenesis. Induction of DNA double-strand breaks (DSBs) is the initial event after radiation exposure, which can potentially lead to carcinogenesis, but the dynamics of DSB induction and repair are not well understood at the tissue level. In this study, we used female rats, which have been recognized as a useful experimental model for studying radiation effects on the mammary gland. We focused on differences in DSB kinetics among basal cells, luminal progenitor and mature cells in different parts of the mammary duct. 53BP1 foci were used as surrogate markers of DSBs, and 53BP1 foci in each mammary epithelial cell in immunostained tissue sections were counted 1-24 h after irradiation and fitted to an exponential function of time. Basal cells were identified as cytokeratin (CK) 14+ cells, luminal progenitor cells as CK8 + 18low cells and luminal mature cells as CK8 + 18high cells. The number of DSBs per nucleus tended to be higher in luminal cells than basal cells at 1 h post-irradiation. A model analysis indicated that basal cells in terminal end buds (TEBs), which constitute the leading edge of the mammary duct, had significantly fewer initial DSBs than the two types of luminal cells, and there was no significant difference in initial amount among the cell types in the subtending duct. The repair rate did not differ among mammary epithelial cell types or their locations. Thus, luminal progenitor and mature cells are more susceptible to radiation-induced DSBs than are basal cells in TEBs.

A Monte Carlo simulation was used to assess the performance of a collimated hollow X-ray microbeam for subcellular cytoplasm irradiation. A high-Z coaxial collimation structure with an inner core for nucleus shielding was investigated. Two key performances, the extraction efficiency (cytoplasm dose per unit incident fluence) and the dose contrast (cytoplasm-to-nucleus dose ratio), were evaluated regarding the influences of the material, geometry and physical arrangements of the collimator, target dish and incident beam source. Simulation results demonstrate that a gold coaxial structure with a practical collimation geometry of a 1-mm length, 10-μm inner diameter and 200-μm outer diameter, with the top exit closely attached (with a minimized air gap) to the bottom of a cell dish with a 3-μm thick Mylar film is recommended for cytoplasm irradiation of adherent mammalian cells. For a synchrotron source in the energy range < 10 keV, a dose contrast of approximately 100 can be achieved. For a bremsstrahlung source <30-kV tube voltage, a dose contrast of approximately 50-100 can still be achieved. General principles are summarized with further explanations of the performance of the hollow X-ray microbeam.

X-ray therapy aims to eliminate tumours while minimizing side effects. Intense mucositis is sometimes induced when irradiating the oral cavity with a dental metal crown (DMC). However, the underlying mechanisms of such inducing radiosensitization by DMC remain uncertain. This study explored the radiosensitizing mechanisms around DMCs in an interdisciplinary approach with cell experiments and Monte Carlo simulation with the PHITS code. Clonogenic survival and nuclear 53BP1 foci of a cell line derived from cervical cancer cells (HeLa cells) were measured post-irradiation with therapeutic X-rays near high-Z materials such as Pb or Au plates, and the experimental sensitizer enhancement ratio (SER) was obtained. Meanwhile, the dose enhancement ratio (DER) and relative biological effectiveness for DNA damage yields were calculated using the PHITS code, by considering the corresponding experimental condition. The experiments show the experimental SER values for cell survival and 53BP1 foci near metals are 1.2-1.4, which agrees well with the calculated DER values. These suggest that the radiosensitizing effects near metal are predominantly attributed to the dose increase. In addition, as a preclinical evaluation, the spatial distributions of DER near DMC are calculated using Computed Tomography Digital Imaging and Communications in Medicine (CT-DICOM) data and a simple tooth model. As a result, the DER values evaluated using the CT-DICOM data were lower than those from a simple tooth model. These findings highlight the challenge of evaluating radiosensitizing effects near DMCs using Digital Imaging and Communications in Medicine (DICOM) images due to volume-averaging effects and emphasize the need for a high-resolution (<1 mm) dose assessment method unaffected by these effects.

The repair of DNA double-strand breaks is a crucial yet delicate process which is affected by a multitude of factors. In this study, our goal is to analyse the influence of the linear energy transfer (LET) on the DNA repair kinetics. By utilizing the database of repair of DNA and aggregating the results of 84 experiments, we conduct various model fits to evaluate and compare different hypothesis regarding the effect of LET on the rejoining of DNA ends. Despite the considerable research efforts dedicated to this topic over the past decades, our findings underscore the complexity of the relationship between LET and DNA repair kinetics. This study leverages big data analysis to capture overall trends that single experimental studies might miss, providing a valuable model for understanding how radiation quality impacts DNA damage and subsequent biological effects. Our results highlight the gaps in our current understanding, emphasizing the pressing need for further investigation into this phenomenon.

Intracavitary brachytherapy with a remote after-loading system (RALS) is performed as a part of radical radiation therapy in cervical cancer. The radiation source is delivered directly through an applicator placed inside the uterus or vagina. Thorough quality control is important to prevent accidents that can lead to serious irradiation error, and an applicator check is one such quality control measure. We experienced a clinical situation in which a small volume of water was observed in the lumen of a post-sterilized applicator on treatment-planning CT. Although the submersion test was negative and no air bubbles emerged from the applicator, ultra-high-resolution computed tomography (U-HRCT) showed a linear crack reaching the inside of the applicator. This abnormality was not identified on treatment-planning CT, which has lower spatial resolution than U-HRCT. In addition, no linear cracks were seen on U-HRCT images of eight other applicators considered to be free from damage. U-HRCT may have superior potential to detect applicator damage and could be useful for quality assurance of the RALS procedure.

Purpose of this study is to evaluate patient characteristics, treatments and outcomes in bone metastasis radiotherapy practice. Patients for whom radiotherapy for bone metastasis was planned at 26 institutions in Japan between December 2020 and March 2021 were consecutively registered in this prospective, observational study. Study measures included patient characteristics, pain relief, skeletal-related events (SREs), overall survival and incidence of radiation-related adverse events. Pain was evaluated using a numerical rating scale (NRS) from 0 to 10. Irradiated dose was analyzed by the biologically effective dose (BED) assuming α/β = 10. Overall, 232 patients were registered; 224 patients and 302 lesions were fully analyzed. Eastern Cooperative Oncology Group Performance Status was 0/1/2/3/4 in 23%/38%/22%/13%/4%; 59% of patients had spinal metastases and 84% had painful lesions (NRS ≥ 2). BED was <20 Gy (in 27%), 20-30 Gy (24%), 30-40 Gy (36%) and ≥ 40 Gy (13%); 9% of patients were treated by stereotactic body radiotherapy. Grade 3 adverse events occurred in 4% and no grade 4-5 toxicity was reported. Pain relief was achieved in 52% at 2 months. BED is not related to pain relief. The cumulative incidence of SREs was 6.5% (95% confidence interval (CI) 3.1-9.9) at 6 months; no factors were significantly associated with SREs. With spinal lesions, 18% of patients were not ambulatory at baseline and 50% of evaluable patients in this group could walk at 2 months. The 6-month overall survival rate was 70.2% (95% CI 64.2-76.9%). In conclusion, we report real-world details of radiotherapy in bone metastasis.