Pellicioli P, Donzelli M, Davis J A, Estève F, Hugtenburg R, Guatelli S, Petasecca M, Lerch M L F, Bräuer-Krisch E, Krisch M
ID17 Biomedical Beamline, ESRF - The European Synchrotron, 71 avenue des Martyrs, Grenoble, France.
School of Physics, University of Wollongong, Wollongong, Australia.
J Synchrotron Radiat. 2021 Mar 1;28(Pt 2):392-403. doi: 10.1107/S1600577520016811. Epub 2021 Feb 9.
Microbeam radiation therapy (MRT) is a developing radiotherapy, based on the use of beams only a few tens of micrometres wide, generated by synchrotron X-ray sources. The spatial fractionation of the homogeneous beam into an array of microbeams is possible using a multislit collimator (MSC), i.e. a machined metal block with regular apertures. Dosimetry in MRT is challenging and previous works still show differences between calculated and experimental dose profiles of 10-30%, which are not acceptable for a clinical implementation of treatment. The interaction of the X-rays with the MSC may contribute to the observed discrepancies; the present study therefore investigates the dose contribution due to radiation interaction with the MSC inner walls and radiation leakage of the MSC. Dose distributions inside a water-equivalent phantom were evaluated for different field sizes and three typical spectra used for MRT studies at the European Synchrotron Biomedical beamline ID17. Film dosimetry was utilized to determine the contribution of radiation interaction with the MSC inner walls; Monte Carlo simulations were implemented to calculate the radiation leakage contribution. Both factors turned out to be relevant for the dose deposition, especially for small fields. Photons interacting with the MSC walls may bring up to 16% more dose in the valley regions, between the microbeams. Depending on the chosen spectrum, the radiation leakage close to the phantom surface can contribute up to 50% of the valley dose for a 5 mm × 5 mm field. The current study underlines that a detailed characterization of the MSC must be performed systematically and accurate MRT dosimetry protocols must include the contribution of radiation leakage and radiation interaction with the MSC in order to avoid significant errors in the dose evaluation at the micrometric scale.
微束放射疗法（MRT）是一种正在发展的放射疗法，它基于使用由同步加速器X射线源产生的仅几十微米宽的束流。利用多缝准直器（MSC），即带有规则孔径的加工金属块，可将均匀束流在空间上分割成微束阵列。MRT中的剂量测定具有挑战性，先前的研究仍表明计算出的和实验测得的剂量分布之间存在10% - 30%的差异，这对于治疗的临床应用来说是不可接受的。X射线与MSC的相互作用可能导致了所观察到的差异；因此，本研究调查了由于辐射与MSC内壁的相互作用以及MSC的辐射泄漏所产生的剂量贡献。针对欧洲同步加速器生物医学束线ID17用于MRT研究的不同射野尺寸和三种典型光谱，评估了水等效模体内部的剂量分布。使用胶片剂量测定法来确定辐射与MSC内壁相互作用的贡献；采用蒙特卡罗模拟来计算辐射泄漏的贡献。结果表明这两个因素对于剂量沉积都很重要，尤其是对于小射野。与MSC壁相互作用的光子可能在微束之间的谷区带来高达16%的额外剂量。根据所选光谱，对于5 mm×5 mm的射野，靠近模体表面的辐射泄漏对谷区剂量的贡献可能高达50%。当前研究强调，必须系统地对MSC进行详细表征，准确的MRT剂量测定方案必须包括辐射泄漏以及辐射与MSC相互作用的贡献，以避免在微米尺度的剂量评估中出现重大误差。
