Jung Seongmoon, Kim In Jung, Yi Chul-Young, Kim Yun Ho, Seong Young Min, Solomon Rukundo, Choi Sang Hyoun, Jang Young-Jae, Lee Se Byeong, Kim Chae-Eon, Pak Sang-Il, Park Jong In
Ionizing Radiation Metrology Group, Korea Research Institute of Standards and Science, Daejeon, Republic of Korea.
Precision Measurement Engineering, University of Science and Technology, Daejeon, Republic of Korea.
Med Phys. 2025 Oct;52(10):e70022. doi: 10.1002/mp.70022.
Ultra-high dose rate (UHDR) radiotherapy, or FLASH RT, has shown potential to spare normal tissues while maintaining tumor control. However, accurate dosimetry at UHDR remains challenging, as conventional ionization chambers suffer from recombination effects. Although radiochromic films and alanine dosimeters have both been investigated independently for FLASH dosimetry, their separate use hinders robust validation and direct comparison of their measurements.
This study aims to develop and evaluate a unified dosimeter containing both alanine and radiochromic film for electron and proton FLASH beam dosimetry. The design allows for simultaneous, co-located irradiation of both dosimeter types, enabling a direct comparison between them. This configuration eliminates confounding factors such as positional offsets, alignment errors, and beam fluctuations, thereby facilitating the validation of measurements and enhancing confidence in FLASH dosimetry.
The unified alanine and EBT-XD/HD-V2 film dosimeter was designed with the same outer dimensions as the Advanced Markus chamber (PTW-Freiburg), allowing compatibility with commercial QA phantoms. Alanine and film dosimeters were calibrated under conventional electron and proton beams, traceable to absorbed dose to water from Co-60 gamma rays. The unified dosimeter was used to measure dose from a 9 MeV electron FLASH beam (Varian Clinac iX) and a 230 MeV proton FLASH beam (IBA machine), with alanine and film irradiated simultaneously at the same location.
The alanine dosimeter measured the dose per pulse, instantaneous dose rate, and mean dose rate at a source-to-surface distance of 100 cm for the electron FLASH beam as 0.99 0.02 Gy/pulse, 2.48 10 Gy/s, and 357 Gy/s, respectively. The EBT-XD film showed good agreement (within a 2.0% relative difference) in the 10-30-Gy range, whereas the HD-V2 indicated a larger difference (up to 5.9%) compared to the alanine dosimeter. The mean dose rate for the proton FLASH beam, measured by the alanine dosimeter, was 115.4 1.1 Gy/s. The EBT-XD showed a 4.3% relative difference with the alanine dosimeter in the 10-30-Gy range.
The unified alanine and film dosimeters enabled simultaneous irradiation of the alanine and the films, with combined relative standard uncertainties of 2.4% (k = 1) for the alanine dosimeter and 3.5% (k = 1) for the EBT-XD films at the electron FLASH beam. For the proton FLASH beam, these uncertainties were 3.2% (k = 1) for both the alanine dosimeter and the EBT-XD films. Until dosimetry guidelines for the FLASH RT community are established by a working group such as AAPM TG-359, the dosimetry protocol proposed in this study can serve as a promising approach for FLASH RT facilities worldwide.
超高剂量率（UHDR）放疗，即FLASH放疗，已显示出在维持肿瘤控制的同时保护正常组织的潜力。然而，由于传统电离室存在复合效应，UHDR下的精确剂量测定仍然具有挑战性。尽管放射变色薄膜和丙氨酸剂量计都已分别用于FLASH剂量测定的研究，但它们的单独使用阻碍了测量结果的可靠验证和直接比较。
本研究旨在开发和评估一种包含丙氨酸和放射变色薄膜的统一剂量计，用于电子和质子FLASH束剂量测定。该设计允许同时对两种剂量计类型进行共定位照射，从而实现它们之间的直接比较。这种配置消除了诸如位置偏移、对准误差和束流波动等混杂因素，从而便于测量验证并增强对FLASH剂量测定的信心。
统一的丙氨酸和EBT-XD/HD-V2薄膜剂量计的设计尺寸与Advanced Markus电离室（PTW-弗莱堡）相同，以便与商业质量保证体模兼容。丙氨酸和薄膜剂量计在传统电子束和质子束下进行校准，可追溯到Co-60伽马射线对水的吸收剂量。使用统一剂量计测量来自9 MeV电子FLASH束（瓦里安Clinac iX）和230 MeV质子FLASH束（IBA机器）的剂量，丙氨酸和薄膜在同一位置同时照射。
对于电子FLASH束，丙氨酸剂量计在源皮距100 cm处测量的每脉冲剂量、瞬时剂量率和平均剂量率分别为0.99±0.02 Gy/脉冲、2.48×10 Gy/s和357 Gy/s。EBT-XD薄膜在10 - 30 Gy范围内显示出良好的一致性（相对差异在2.0%以内），而HD-V2薄膜与丙氨酸剂量计相比差异较大（高达5.9%）。丙氨酸剂量计测量的质子FLASH束平均剂量率为115.4±1.1 Gy/s。EBT-XD薄膜在10 - 30 Gy范围内与丙氨酸剂量计的相对差异为4.3%。
统一的丙氨酸和薄膜剂量计能够同时照射丙氨酸和薄膜，对于电子FLASH束，丙氨酸剂量计的组合相对标准不确定度为2.4%（k = 1），EBT-XD薄膜为3.5%（k = 1）。对于质子FLASH束，丙氨酸剂量计和EBT-XD薄膜的这些不确定度均为3.2%（k = 1）。在诸如AAPM TG-359等工作组制定FLASH放疗社区的剂量测定指南之前，本研究中提出的剂量测定方案可作为全球FLASH放疗设施的一种有前景的方法。
