碳离子束三维吸收剂量探测系统研制

While comparing with the photon therapy, there is a significant advantage from the carbon-ion radiotherapy which delivers its dose to the target much more precisely and effectively. In the meanwhile, it raises the demand of a beam quality and control system which must be fast and robust ，also with a 3D dose distribution detector system, which can be used as 3D dose checking system to confirm the beam delivery system sending the beam to the expected target. This project would develop a prototype detector system for 3D dose distribution of carbon ion radiotherapy. The detector system is composed of two pixel ionization chambers that its area of the pixel is not bigger than the (2.5×2.5) mm2, two strip ionization chambers and about one hundred parallel-plate ionization chambers. After well calibrated, it can obtain the carbon ion dose absorption at the target directly. The full measurement can be finished in one minute. The spatial resolution is better than 1 mm in longitudinal direction for the dose absorption, and better than 0.3 mm in transversal direction for the beam position and Bragg-Peak. The system could be used to optimize treatment plan and verify beam delivery system. Compare the results with the CT and PET image could make a more reasonable and secure treatment plan. As more and more new carbon-ion therapy instruments are deployed, the potential market and commercial value of this detector system is going to increase.

相比于光子，使用碳离子治疗肿瘤最显著的优势就是其剂量可以被精确定位到靶区。想要充分发挥这一优势就需要好的束流，快速可靠的控制系统，以及可以直接测量三维剂量的探测系统来验证束流配送系统是否能将束流输送到预期的靶位。本课题将研制用于碳离子治疗装置的束流三维吸收剂量测量的探测器样机。这套系统由两套像素点不大于（2.5×2.5）mm2的像素电离室、两套阳极条电离室、一百套平板电离室组成。经过标准剂量电离室的刻度能直接测量三维吸收剂量值，能在加速器状态完全不变的情况下1分钟内完成测量。其中深度剂量测量精度好于1mm，横向束流位置精度好于0.3mm，Bragg峰位置测量精度好于0.3mm。这套系统将用于适形治疗计划、束流配送系统的验证，将其测量结果与PET、CT得到的肿瘤图像相对比可制定出更合理，更安全的治疗计划。随着碳离子治疗装置数量的增加，这套系统潜在的应用市场也将扩大，将具有较高的商业价值。

在项目经费的支持下，项目组按照项目计划研制了基于FPGA控制的高集成度ASIC芯片实现了前端电子学及数据采集，将高压及环境监测集成到前端，消除了电子学的死时间，将信噪比提高约一个量级，系统采样频率提高了2倍。按照项目计划研制了由50套平板电离室，两套阳极条电离室及支架组合而成的复合电离室阵列，实现同步采样，进行了在束实验。2021年5月份的束流实验使用台阶形靶、球面靶和斜面靶测量的数据训练机器学习网络，然后使用该网络成功预测了未知斜面靶，实现了粒子照相功能。目前，使用这种复合型电离室，通过深度学习算法实现粒子照相功能的探测系统还未见公开报道。这套系统测量束流位置精度达到0.25 mm,测量Bragg峰位置精度好于0.2 mm，粒子照相的像素点达到2 mm。