Development of depth dose meter for heavy ion particle beams with piled plastic scintillators

我们继续测试新研制的深度剂量计。采用大阪大学医院直线加速器的x射线（4、10和18 MV）、电子束（6、9、12和15 MeV）、大阪大学RCNP回旋加速器的质子束（65和200 MeV）和近红外光谱仪千叶医疗重离子加速器的碳束（290MeV/n）对剂量计进行了测试。在遮光方面，无热压制型纤维块比有热压制型纤维块更适合于传感器。利用数字滤波器可以在获取图像数据时减小背景信号。在补偿切伦科夫光对X射线和电子束的影响、高能质子束对光的猝灭作用后，电离室的深度剂量数据与新型剂量计的深度剂量数据吻合良好。通过补偿纤维块的光发射特性，使误差减小。我们可以测量碳单峰光束的深度剂量曲线。但对于含有不同LET成分的分散碳梁，差异很大。还有很大的改进空间。通过对变粒子发光差异的校正，确认了深度剂量计的高质量，我们计划制作更紧凑的三维深度剂量计，使探测器旋转和直线运动。这种新设计的剂量计减少了测量基本剂量分布的时间，是有用的。

We continued to test the new developed depth dose meter. The dosimeter was exposed to x rays (4,10 and 18 MV) and electron beams (6,9,12 and 15 MeV) from Linac at the Osaka University Hospital, proton beams (65 and 200 MeV) from the cyclotron at RCNP of Osaka University and carbon beam (290MeV/n) from the Heavy Ion of Medical Accerator in Chiba of NIRS to test it. The pressed type of fiberblock without heat is more suitable for sensor than that with heat in respect of shielding the light. We could decrease the background signal in obtaining the image data by utilizing the digital filter. The fitness was good between the depth dose data by ionization chamber and by new dosimeter after compensating Cerenkov light for X ray and electron beam, quenching of light by energetic proton beams. The discrepancy became smaller by compensating the characteristics of emission of light from fiberblock. We could measure the depth dose curve for mono peak beam of carbon. But the discrepancy was large for spread outed carbon beams containing different components of LET.There are much room for improvement. After confirming the high quality of depth dose meter by correcting the difference of light emission by variable particles, we have a plan to make more compact 3D depth dose meter with rotation and rectilinear motion of detector. Such a new designed dosimeter will be useful because of reducing time for measurement of the fundamental dose distribution.