Nakaoka Ai, Hotta Kenji, Matsuura Taeko, Hoshino Yoshihiko, Tachibana Hidenobu
Radiation Safety and Quality Assurance Division, National Cancer Center Hospital East, Chiba, Japan.
Division of Applied Quantum Science and Engineering Faculty of Engineering, Hokkaido University, Hokkaido, Japan.
J Appl Clin Med Phys. 2025 Jul;26(7):e70165. doi: 10.1002/acm2.70165.
Gel dosimeters enable three-dimensional dose measurement in x-ray and charged-particle therapies. A normoxic N-vinylpyrrolidone-based polymer gel (VIPET) dosimeter is expected to provide high-precision proton dose measurements. However, reports on the fundamental performance of VIPET gel dosimeters in proton beam measurement are limited, and the accuracy of position and dose measurements still needs to be determined.
We evaluated the accuracy of the VIPET gel dosimeter in proton beam measurement.
Proton beams of 190 MeV were delivered at dose rates of 2 and 8 Gy/min, and N-vinylpyrrolidone-based polymer gel dosimeters containing an inorganic salt as a sensitizer (iVIPET) were irradiated with a 10 × 10 cm field and doses of up to 30 Gy. Magnetic resonance imaging was used for imaging. Key parameters assessed included R2 - dose linearity, dose uncertainty and resolution, dose reproducibility, energy (linear energy transfer [LET]) dependence, dose rate dependence, dose uniformity, and stopping power ratio (SPR).
A strong linear relationship was observed in the 0-30 Gy range. Dose uncertainties were in the range 1%-3%. Three sets of percentage depth dose measurements showed good agreement within 1.6%. Energy (LET) dependence led to measured peak doses being 23% lower than the treatment planning system (TPS) calculations. Proton energy effects in the plateau region were limited and dose rate effects were not recognized. Beam profiles in the axes parallel and perpendicular to the beam axis showed variations of approximately 1.2% and 1.3%, respectively, compared with the TPS calculations. The SPR was consistent with the TPS derived from CT values (1.03).
The VIPET dosimeter showed high reproducibility and uniformity in range and dose measurements of proton therapy beams without energy dependency in the plateau region or dose rate dependency in 2-8 Gy/min. The dosimeter also showed energy (LET) dependence comparable with that reported in previous studies.
凝胶剂量计可用于X射线和带电粒子治疗中的三维剂量测量。一种基于常氧N - 乙烯基吡咯烷酮的聚合物凝胶（VIPET）剂量计有望实现高精度的质子剂量测量。然而，关于VIPET凝胶剂量计在质子束测量中的基本性能的报道有限，其位置和剂量测量的准确性仍有待确定。
我们评估了VIPET凝胶剂量计在质子束测量中的准确性。
以2和8 Gy/min的剂量率输送190 MeV的质子束，用含有无机盐作为敏化剂的基于N - 乙烯基吡咯烷酮的聚合物凝胶剂量计（iVIPET）在10×10 cm的射野下进行照射，剂量高达30 Gy。使用磁共振成像进行成像。评估的关键参数包括R2 - 剂量线性、剂量不确定度和分辨率、剂量可重复性、能量（线能量转移[LET]）依赖性、剂量率依赖性、剂量均匀性和阻止本领比（SPR）。
在0 - 30 Gy范围内观察到很强的线性关系。剂量不确定度在1% - 3%范围内。三组百分深度剂量测量结果在1.6%以内显示出良好的一致性。能量（LET）依赖性导致测量的峰值剂量比治疗计划系统（TPS）计算值低23%。质子能量在坪区的影响有限，未识别出剂量率影响。与TPS计算相比，平行和垂直于射束轴的轴向上的射束轮廓分别显示出约1.2%和1.3%的变化。SPR与从CT值得出的TPS一致（1.03）。
VIPET剂量计在质子治疗束的射程和剂量测量中显示出高可重复性和均匀性，在坪区无能量依赖性，在2 - 8 Gy/min范围内无剂量率依赖性。该剂量计还显示出与先前研究报道相当的能量（LET）依赖性。
