0.35TMR 直线加速器调试用的磁共振兼容探测器评估。

MR compatible detectors assessment for a 0.35 T MR-linac commissioning.

机构信息

Medical Physics Department, Pitié-Salpêtrière Hospital, AP-HP Sorbonne University, 47-83 Boulevard de l'Hôpital, 75651, Paris Cedex 13, France.

Institut de Radioprotection et Sûreté Nucléaire (IRSN), PSE-SANTE/SDOS/LDRI, 92260, Fontenay-aux-Roses, France.

出版信息

Radiat Oncol. 2024 Mar 20;19(1):40. doi: 10.1186/s13014-024-02431-8.

DOI:10.1186/s13014-024-02431-8

PMID:38509543

原文链接:https://pmc.ncbi.nlm.nih.gov/articles/PMC10956263/

Abstract

PURPOSE

To assess a large panel of MR compatible detectors on the full range of measurements required for a 0.35 T MR-linac commissioning by using a specific statistical method represented as a continuum of comparison with the Monte Carlo (MC) TPS calculations. This study also describes the commissioning tests and the secondary MC dose calculation validation.

MATERIAL AND METHODS

Plans were created on the Viewray TPS to generate MC reference data. Absolute dose points, PDD, profiles and output factors were extracted and compared to measurements performed with ten different detectors: PTW 31010, 31021, 31022, Markus 34045 and Exradin A28 MR ionization chambers, SN Edge shielded diode, PTW 60019 microdiamond, PTW 60023 unshielded diode, EBT3 radiochromic films and LiF µcubes. Three commissioning steps consisted in comparison between calculated and measured dose: the beam model validation, the output calibration verification in four different phantoms and the commissioning tests recommended by the IAEA-TECDOC-1583.

MAIN RESULTS

The symmetry for the high resolution detectors was higher than the TPS data of about 1%. The angular responses of the PTW 60023 and the SN Edge were - 6.6 and - 11.9% compared to the PTW 31010 at 60°. The X/Y-left and the Y-right penumbras measured by the high resolution detectors were in good agreement with the TPS values except for the PTW 60023 for large field sizes. For the 0.84 × 0.83 cm field size, the mean deviation to the TPS of the uncorrected OF was - 1.7 ± 1.6% against - 4.0 ± 0.6% for the corrected OF whereas we found - 4.8 ± 0.8% for passive dosimeters. The mean absolute dose deviations to the TPS in different phantoms were 0 ± 0.4%, - 1.2 ± 0.6% and 0.5 ± 1.1% for the PTW 31010, PTW 31021 and Exradin A28 MR respectively.

CONCLUSIONS

The magnetic field effects on the measurements are considerably reduced at low magnetic field. The PTW 31010 ionization chamber can be used with confidence in different phantoms for commissioning and QA tests requiring absolute dose verifications. For relative measurements, the PTW 60019 presented the best agreement for the full range of field size. For the profile assessment, shielded diodes had a behaviour similar to the PTW 60019 and 60023 while the ionization chambers were the most suitable detectors for the symmetry. The output correction factors published by the IAEA TRS 483 seem to be applicable at low magnetic field pending the publication of new MR specific values.

摘要

目的

使用一种特殊的统计方法，该方法以蒙特卡罗 (MC) TPS 计算的连续比较表示，评估在 0.35T MR 直线加速器的全面测量范围内适用于多种 MR 兼容探测器。本研究还描述了调试测试和二次 MC 剂量计算验证。

材料和方法

在 Viewray TPS 上创建计划，以生成 MC 参考数据。提取绝对剂量点、PDD、曲线和输出因子，并与十种不同探测器的测量值进行比较：PTW 31010、31021、31022、Markus 34045 和 Exradin A28 MR 电离室、SN Edge 屏蔽二极管、PTW 60019 微钻石、PTW 60023 无屏蔽二极管、EBT3 放射色胶片和 LiF µcubes。调试测试分为三个步骤：在计算和测量剂量之间进行比较：光束模型验证、在四个不同的体模中进行输出校准验证以及 IAEA-TECDOC-1583 推荐的调试测试。

主要结果

高分辨率探测器的对称性比 TPS 数据高约 1%。在 60°时，PTW 60023 和 SN Edge 的角度响应分别比 PTW 31010 低-6.6%和-11.9%。高分辨率探测器测量的 X/Y-左和 Y-右半影与 TPS 值一致，除了大射野尺寸的 PTW 60023 外。对于 0.84×0.83cm 射野尺寸，未校正的 OF 的平均偏差到 TPS 的值为-1.7±1.6%，而校正的 OF 的值为-4.0±0.6%，而无源剂量计为-4.8±0.8%。在不同的体模中，与 TPS 的平均绝对剂量偏差为 PTW 31010、PTW 31021 和 Exradin A28 MR 分别为 0±0.4%、-1.2±0.6%和 0.5±1.1%。

结论

在低磁场下，磁场对测量的影响大大降低。PTW 31010 电离室可在不同的体模中用于调试和 QA 测试，这些测试需要进行绝对剂量验证。对于相对测量，PTW 60019 在整个射野范围内具有最佳的一致性。对于曲线评估，屏蔽二极管的行为类似于 PTW 60019 和 60023，而电离室是最适合用于对称性的探测器。IAEA TRS 483 发布的输出校正因子似乎适用于低磁场，有待新的 MR 特定值的发布。