CyberKnife剂量校准与验证的系统研究

CyberKnife系统采用小射野对患者肿瘤实施立体定向放射治疗，提供了更好的适形剂量分布和更大的剂量梯度，从而使靶区得到大剂量照射的同时很好地保护了周围的正常组织器官。然而由于小射野下束流电子不平衡状态的出现，以及探测器介质及体积的影响带来了临床剂量测量、计算及评估上的困难。本研究基于对CyberKnife系统进行精确的Monte Carlo模拟，研究各类探测器在非标准野及小野下的剂量响应并计算其修正因子，应用国际上最新推荐的剂量学体系，实施非标准参考野下的绝对剂量校准以及小野输出因子的精确测量，将有效地推动国内和国际上非标准野及小野下新剂量体系的建立和发展。本研究进而采用模体实验与蒙卡模拟相结合的方法，对CyberKnife系统患者治疗计划进行点剂量和平面剂量分布的验证，研究组织非均匀性对剂量计算的影响，建立CyberKnife系统特定患者质量保证（PSQA）的技术方法和临床规范。

CyberKnife System use small fields for Stereotactic Radiosurgery(SRS),offer a very conformal and gradient dose distribution and protect the normal tissue very well at the time of giving the target enough dose. However, electrons nonequilibrium caused by small fields and the effects of material and volume of detectors makes the measurement、calculation and evaluation of dosimetry very difficult. This research will simulate CyberKnife system with Monte Carlo method precisely,investigate the dose response of many detectors and calculate their correction factors, implant a recently proposed dosimetric formalism to CyberKnife system, calibrate the CyberKnife beam under nonstandard reference condition and measure the output factors under small fields very accurately, help the international working group to develop the dosemetry protocals of nonstandard and small fields. This research also try to use experiments on phantom and Monte Carlo simulation to evaluate the treatment plan of patients, research the effect of tissue nonuniform on dose calculation,develop a standardized patients specific quality assurance(PSQA).