Evaluation of detectors for acquisition of pristine depth-dose curves in pencil beam scanning
Evaluation of detectors for acquisition of pristine depth-dose curves in pencil beam scanning
复制标题
DOI：
10.1120/jacmp.v16i6.5577
复制
发表时间：
2015-01-01
影响因子：
2.1
通讯作者：
Talla, Patrick Takoukam
中科院分区：
文献类型：
--
作者：
Baeumer, Christian;Koska, Benjamin;Talla, Patrick Takoukam
获取准单能（“原始”）深度剂量曲线是质子治疗头的调试和质量保证框架中的一项重要任务。对于笔形束扫描传输模式，这通常是通过测量垂直于未扫描束轴的平面中的积分电离来实现的。我们重点评估三个整体探测器：其中两个是有效半径分别为 4.1 cm 和 6.0 cm 的平面平行电离室，安装在扫描水体模中。第三个集成探测器是一个半径为 6.0 厘米的多层电离室。实验结果与小半径平面平行室和小半径多层电离室在宽场条件下的相应测量进行了比较。我们通过评估深度-剂量曲线的形状、相对电荷收集效率以及比较测量范围，研究了原始质子场的测量深度-剂量曲线如何取决于检测装置。我们的结果表明，将整体腔室的半径从 4.1 cm 增加到 6.0 cm 可使收集效率提高 0%-3.5%，具体取决于光束能量和深度。常规范围可通过大电极多层电离室确定，典型不确定度为 0.4 mm。大电极多层电离室在布拉格峰区域表现出较小的畸变。这禁止将其用于获取基础数据，但对于质量保证来说是可以接受的。与小电极对应物的直接比较表明，良好的范围精度和峰值失真是多层电离室设计的特征。
Acquisition of quasi-monoenergetic ("pristine") depth-dose curves is an essential task in the frame of commissioning and quality assurance of a proton therapy treatment head. For pencil beam scanning delivery modes this is often accomplished by measuring the integral ionization in a plane perpendicular to the axis of an unscanned beam. We focus on the evaluation of three integral detectors: two of them are plane-parallel ionization chambers with an effective radius of 4.1 cm and 6.0 cm, respectively, mounted in a scanning water phantom. The third integral detector is a 6.0 cm radius multilayer ionization chamber. The experimental results are compared with the corresponding measurements under broad field conditions, which are performed with a small radius plane-parallel chamber and a small radius multilayer ionization chamber. We study how a measured depth-dose curve of a pristine proton field depends on the detection device, by evaluating the shape of the depth-dose curve, the relative charge collection efficiency, and intercomparing measured ranges. Our results show that increasing the radius of an integral chamber from 4.1 cm to 6.0 cm increases the collection efficiency by 0%-3.5% depending on beam energy and depth. Ranges can be determined by the large electrode multilayer ionization chamber with a typical uncertainty of 0.4 mm on a routine basis. The large electrode multilayer ionization chamber exhibits a small distortion in the Bragg Peak region. This prohibits its use for acquisition of base data, but is tolerable for quality assurance. The good range accuracy and the peak distortion are characteristics of the multilayer ionization chamber design, as shown by the direct comparison with the small electrode counterpart.