Fournier P, Crosbie J C, Cornelius I, Berkvens P, Donzelli M, Clavel A H, Rosenfeld A B, Petasecca M, Lerch M L F, Bräuer-Krisch E
Centre for Medical Radiation Physics, University of Wollongong, New South Wales, Australia.
Phys Med Biol. 2016 Jul 21;61(14):N349-61. doi: 10.1088/0031-9155/61/14/N349. Epub 2016 Jul 1.
Microbeam radiation therapy (MRT) is a new radiation treatment modality in the pre-clinical stage of development at the ID17 Biomedical Beamline of the European synchrotron radiation facility (ESRF) in Grenoble, France. MRT exploits the dose volume effect that is made possible through the spatial fractionation of the high dose rate synchrotron-generated x-ray beam into an array of microbeams. As an important step towards the development of a dosimetry protocol for MRT, we have applied the International Atomic Energy Agency's TRS 398 absorbed dose-to-water protocol to the synchrotron x-ray beam in the case of the broad beam irradiation geometry (i.e. prior to spatial fractionation into microbeams). The very high dose rates observed here mean the ion recombination correction factor, k s , is the most challenging to quantify of all the necessary corrections to apply for ionization chamber based absolute dosimetry. In the course of this study, we have developed a new method, the so called 'current ramping' method, to determine k s for the specific irradiation and filtering conditions typically utilized throughout the development of MRT. Using the new approach we deduced an ion recombination correction factor of 1.047 for the maximum ESRF storage ring current (200 mA) under typical beam spectral filtering conditions in MRT. MRT trials are currently underway with veterinary patients at the ESRF that require additional filtering, and we have estimated a correction factor of 1.025 for these filtration conditions for the same ESRF storage ring current. The protocol described herein provides reference dosimetry data for the associated Treatment Planning System utilized in the current veterinary trials and anticipated future human clinical trials.
微束放射治疗（MRT）是一种处于临床前开发阶段的新型放射治疗方式，在法国格勒诺布尔的欧洲同步辐射装置（ESRF）的ID17生物医学光束线开展相关研究。MRT利用了剂量体积效应，这是通过将高剂量率同步加速器产生的X射线束空间分割成微束阵列来实现的。作为制定MRT剂量测定方案的重要一步，我们已将国际原子能机构的TRS 398水吸收剂量方案应用于宽束照射几何条件下（即在空间分割成微束之前）的同步加速器X射线束。此处观察到的极高剂量率意味着，对于基于电离室的绝对剂量测定所需的所有校正而言，离子复合校正因子ks是最难量化的。在本研究过程中，我们开发了一种新方法，即所谓的“电流斜坡”方法，以确定MRT整个开发过程中通常使用的特定照射和过滤条件下的ks。使用这种新方法，我们推导出在MRT典型束光谱过滤条件下，ESRF储存环最大电流（200 mA）时的离子复合校正因子为1.047。目前ESRF正在对兽医患者进行MRT试验，这些试验需要额外的过滤，对于相同的ESRF储存环电流，我们估计这些过滤条件下的校正因子为1.025。本文所述方案为当前兽医试验及预期未来人体临床试验中使用的相关治疗计划系统提供了参考剂量测定数据。
