为实现超高剂量率照射而对临床直线加速器进行改造。

Modifying a clinical linear accelerator for delivery of ultra-high dose rate irradiation.

机构信息

Radiation Physics, Department of Hematology, Oncology and Radiation Physics, Skåne University Hospital, Lund University, Sweden.

Division of Oncology and Pathology, Clinical Sciences, Lund, Skåne University Hospital, Lund University, Sweden.

出版信息

Radiother Oncol. 2019 Oct;139:40-45. doi: 10.1016/j.radonc.2019.01.031. Epub 2019 Feb 10.

DOI:10.1016/j.radonc.2019.01.031

PMID:30755324

Abstract

OBJECTIVES

The purpose of this study was to modify a clinical linear accelerator, making it capable of electron beam ultra-high dose rate (FLASH) irradiation. Modifications had to be quick, reversible, and without interfering with clinical treatments.

METHODS

Performed modifications: (1) reduced distance with three setup positions, (2) adjusted/optimized gun current, modulator charge rate and beam steering values for a high dose rate, (3) delivery was controlled with a microcontroller on an electron pulse level, and (4) moving the primary and/or secondary scattering foils from the beam path.

RESULTS

The variation in dose for a five-pulse delivery was measured to be 1% (using a diode, 4% using film) during 10 minutes after a warm-up procedure, later increasing to 7% (11% using film). A FLASH irradiation dose rate was reached at the cross-hair foil, MLC, and wedge position, with ≥30, ≥80, and ≥300 Gy/s, respectively. Moving the scattering foils resulted in an increased output of ≥120, ≥250, and ≥1000 Gy/s, at the three positions. The beam flatness was 5% at the cross-hair position for a 20 × 20 and a 10 × 10 cm area, with and without both scattering foils in the beam. The beam flatness was 10% at the wedge position for a 6 and 2.5 cm diametric area, with and without the scattering foils in the beam path.

CONCLUSIONS

A clinical accelerator was modified to produce ultra-high dose rates, high enough for FLASH irradiation. Future work aims to fine-tune the dose delivery, using the on-board transmission chamber signal and adjusting the dose-per-pulse.

摘要

目的

本研究旨在对临床直线加速器进行改造，使其能够进行电子束超高剂量率（FLASH）照射。改造必须快速、可逆，且不能干扰临床治疗。

方法

完成的改造包括：（1）通过三个设置位置缩短距离；（2）调整/优化枪电流、调制器充电率和束流转向值，以实现高剂量率；（3）通过电子脉冲级别的微控制器控制输送；（4）移动初级和/或次级散射箔以避开射束路径。

结果

在预热程序后 10 分钟内，五次脉冲输送的剂量变化测量值为 1%（使用二极管时为 4%，使用胶片时为 11%），之后增加到 7%。在十字准线箔、MLC 和楔形位置达到了 FLASH 照射剂量率，分别为≥30、≥80 和≥300 Gy/s。移动散射箔会导致三个位置的输出增加≥120、≥250 和≥1000 Gy/s。在十字准线位置，20×20 和 10×10 cm 面积的束流平坦度为 5%，有和没有两个散射箔在射束中。在楔形位置，有和没有散射箔在射束路径中，6 和 2.5 cm 直径区域的束流平坦度为 10%。