林 直樹

The patient setup using the surface-guided radiation therapy (SGRT) system differs from conventional surface marker procedures. Owing to the abundance of three-dimensional information, there may be operator variability in where to focus during the patient setup. This study aimed to clarify the differences between expert and novice operators in SGRT positioning for head and neck cases by tracking their eye movements, thereby providing data for developing efficient patient setup procedures. Six radiation therapists set up a simulated patient on the SGRT system while recording eye movements on the screen using the QG-PLUS eye-tracking system. The positioning time and number of gaze fixations on the screen were analysed, and the relationship between years of experience with SGRT, positioning time and number of gaze fixations was evaluated. No significant correlation was found between SGRT experience and positioning time (r = -0.67, p = 0.15). However, more experienced radiation therapists exhibited fewer gaze fixations per positioning session (r = -0.81, p < 0.05), indicating that they efficiently identified key positioning points. Additionally, experienced radiation therapists focused more intently on a specific screen during the latter half of positioning, suggesting a refined approach for final patient alignment verification. More experienced radiation therapists showed fewer gaze fixations and demonstrated increased attention to a specific screen during the latter half of the patient setup process, suggesting that eye-tracking technology may provide useful data for standardising patient setup procedures in SGRT patient setups.

To quantify radiation dose reduction in radiotherapy treatment-planning CT (RTCT) using a deep learning-based reconstruction (DLR; AiCE) algorithm compared with adaptive iterative dose reduction (IR; AIDR). To evaluate its potential to inform RTCT-specific diagnostic reference levels (DRLs). In this single-institution retrospective study, 4-part RTCT scans (head, head and neck, lung, and pelvis) were acquired on a large-bore CT. Scans reconstructed with IR (n = 820) and DLR (n = 854) were compared. The 75th-percentile CTDIvol and DLP (CTDIIR, DLPIR vs. CTDIDLR, DLPDLR) were determined per site. Dose reduction rates were calculated as (CTDIDLR - CTDIIR)/CTDIIR × 100% and similarly for DLP. Statistical significance was assessed by the Mann-Whitney U-test. DLR yielded CTDIvol reductions of 30.4-75.4% and DLP reductions of 23.1-73.5% across sites (p < 0.001), with the greatest reductions in head and neck RTCT (CTDIvol: 75.4%; DLP: 73.5%). Variability also narrowed. Compared with published national DRLs, DLR achieved 34.8 mGy and 18.8 mGy lower CTDIvol for head and neck versus UK-DRLs and Japanese multi-institutional data, respectively. DLR substantially lowers RTCT dose indices, providing quantitative data to guide RTCT-specific DRLs and optimize clinical workflows.

BACKGROUND: Accurate absolute dosimetry is essential for achieving high-precision proton beam therapy. Consequently, a comprehensive characterization of the ionization chamber's response properties is necessary. PURPOSE: This study aimed to evaluate the average f Q using Monte Carlo (MC) code PHITS to assess uncertainties among different MC simulation tools. Additionally, P Q values for PTW 30013, NACP-02, and PTW 31013 ionization chambers are calculated using PHITS to provide new reference data for P Q . Furthermore, a new k Q factor for PTW 31013 chamber is established using MC method, contributing to advancements in proton beam dosimetry protocols. METHODS: Monoenergetic proton beams were employed to calculate f Q , k Q , and P Q for Farmer, Semiflex, and plane-parallel chambers. The absorbed dose deposited within the sensitive volume of each chamber was determined via simulations employing PHITS, thereby providing the basis for the estimation of these factors. Computed f Q values were compared with previous reports, while k Q and P Q were benchmarked against literature and Technical Reports Series No. 398 (TRS-398) Rev.1 guideline. RESULTS: Incorporating PHITS-derived f Q values reduced the uncertainty of f ¯ Q P H I T S compared to previous findings. The k Q factor for PTW 31013 followed trends observed in cylindrical chambers with varying sensitive volumes; notably, this study represents the first MC estimation of k Q for this chamber. P Q values for values deviated by up to 1.7% from unity. CONCLUSION: The data generated in this study provide important insights for refining proton beam dosimetry, contributing to the improvement of treatment precision.

This study investigated the effects of preparation temperature and usage period on the relaxation times and apparent diffusion coefficients (ADC) of sucrose phantoms to enhance imaging reliability. Phantoms were prepared using 10% sucrose solutions at 20, 50, and 80 °C. T1 and T2 relaxation times and ADC were monitored over 80 days using magnetic resonance imaging on a 1.5 T system. T2 relaxation time in 50 °C solutions increased from 245.5 to 1579 ms, while 80 °C solutions showed the highest stability (coefficient of variation ≈ 1.8%). T1 relaxation time changes were minimal, and ADC decreased at an average rate of 2.19 × 10-6 mm2/s per day. Bacteria were observed in the sucrose solution, and higher protein concentrations were strongly correlated with decreased 1/T2. In conclusion, sucrose phantoms exhibited temperature-dependent stability, with 80 °C preparations providing the most reliable T2 relaxation time.

Abstract Background Accurate dosimetry is important in radiotherapy, and all equipment used for radiotherapy shoud be audited by an independent external dose audit. Radiophotoluminescence glass dosimeter (RPLD) has excellent characteristics and is widely used for postal dose audit; however, postal dose audit for proton therapy using RPLD has not been established. Purpose This study aims to develop a postal dose audit procedure for scanning proton beams using RPLD, estimate uncertainties, and conduct a multicenter pilot study to validate the methodology. Methods A postal toolkit was developed and a postal dose audit procedure for RPLD measurements of scanning proton beams was established in cooperation with several facilities that employ various accelerators, irradiation equipment, and treatment planning systems (TPS) for clinical use. Based on basic and previous studies, an uncertainty budget was developed for estimating relative uncertainty and pilot studies were conducted at each site. A method for postal dose audits was developed in a multicenter collaboration to develop an approach suitable for implementation across multiple facilities. Results The relative response of 60 RPLDs for scanning proton beam examined in this study was 1.00 ± 1.28% mean ± standard deviation. The combined relative standard uncertainty of postal dosimetry for scanning proton beams using the RPLD was 2.97% (k = 1). Under the reference condition, the maximum differences between the ionization chamber measurement (IC) and TPS, RPLD and TPS, and RPLD and IC were 0.97, 1.88, and 2.12%, respectively. The maximum differences between the RPLD and ionization chamber for plateau measurements at 3 cm depth using single‐energy and non‐reference conditions were 11.31 and 4.02%, respectively. Conclusion We established a procedure for the postal dose audits of proton beams using RPLD and presented the results of a multicenter pilot study. By standardizing the reference conditions, the dosimetry uncertainty was estimated at 2.92%. The results demonstrated the feasibility of performing an independent third‐party dose audit of scanning proton beams using RPLD, and for such postal dose audits for proton beams, the irradiation conditions should be standardized to reduce uncertainties. These results are expected to contribute to the development of proton beams.