低能X线术中放疗系统INTRABEAM的剂量计算与剂量验证研究

The low-energy x-ray INTRABEAM intraoperative radiotherapy (IORT) system provides the tumor bed single-fractional high-dose irradiation in operation process. Its characteristics of significant fall-off dose and higher relative biological effectiveness, ensure to improve the local tumor control rate effectively as well as to maximize the protection of normal tissues. This device does not yet provide three-dimensional dose distribution information and 3D treatment planning system. On the other hand, the new prototype applicators are the lack of comprehensive analysis of dose characteristics and verification study. This program will combine Monte Carlo simulation and experimental measurements to carry out dosimetry research on INTRABEAM: to set up accurate system model and develop dose calculation method based on Monte Carlo simulation; to explore the approaches of dose measurement and verification, and build a perfect and effective dose verification system; to study the dose characteristics in uniform and inhomogeneous tissues, and further achieve the preliminary feasibility study of 3D treatment planning system for virtual surgery/IORT based on patient CT anatomic images. This study will provide intuitive and accurate reference data to radiotherapy doctors for prescription dose given and normal tissue protection. Also expect that the results of this study could promote the development in dosimetry for low-energy x-ray IORT system.

低能X线术中放疗INTRABEAM系统在手术过程中给予瘤床单次大剂量照射，其迅速跌落的剂量特性和较高的相对生物学效应，在有效提高肿瘤局部控制率的同时最大限度地保护正常组织。目前该系统尚未提供系统的三维剂量分布信息和三维计划系统，新型施源器的推广也缺少完善的剂量特性研究。本研究利用蒙特卡罗模拟和实验测量相结合的方法，开展INTRABEAM系统的剂量学研究。建立基于蒙卡模拟的精确系统模型和剂量计算模型；探索剂量测量和验证方法，建立一套针对INTRABEAM系统的完善而有效的剂量验证体系；研究均匀组织和非均匀组织中的剂量分布特性，并进一步实现基于CT解剖图像的虚拟术中放疗三维计划系统的可行性研究；为临床医生处方剂量的给定和正常组织保护提供直观和准确的数据参考。期望本研究能够有助于推动低能X线术中放疗剂量学的发展。

术中放疗系统INTRABEAM采用50 kV低能X线予以瘤床单次大剂量照射，被应用于浅表肿瘤的治疗，在有效提高肿瘤局部控制率的同时更好地保护正常组织。本项目弥补了现有系统提供数据的不足，对该系统的一维二维及三维剂量学特性进行了系统研究。完成了对于裸源及各类施源器完整的电离室水下深度剂量测量，研究了深度剂量曲线拟合方法，基于蒙特卡罗对系统进行几何物理建模及剂量计算，利用背透光胶片在均匀及非均匀等效模体中研究各类施源器的胶片剂量验证方法，对其剂量分布及响应特性进行分析，基于图像的剂量计算的可行性研究。剂量测量、模拟及胶片验证结果有着良好的一致性。本研究为临床上术中放疗适应症的选取、处方剂量的给定和正常组织保护提供直观和准确的数据参考。