超小体积肿瘤立体定向放疗计划的点剂量测量方法  

Absolute point dose measurement of stereotactic radiotherapy plan for ultra-small tumors

作　　者：陈元华 陆中杰[1] CHEN Yuanhua;LU Zhongjie(The First Affiliated Hospital,Zhejiang University School of Medicine,Hangzhou 310003,China)

机构地区：[1]浙江大学医学院附属第一医院放射治疗科,杭州310003

出　　处：《辐射研究与辐射工艺学报》2021年第6期69-76,共8页Journal of Radiation Research and Radiation Processing

摘　　要：针对超小体积肿瘤立体定向放射治疗(SRT)计划,提出电离室实时交叉校准方法来实现绝对点剂量的准确测量。首先将临床SRT放疗计划复制到适配有微型电离室的立体剂量验证模体的CT上,由计划系统(TPS)计算绝对点剂量的理论值。然后每批次测量前,将微型电离室与标准指形电离室进行交叉校准,得出实时交叉校准因子。最后用微型电离室实施测量,并用实时交叉校准因子和标准电离室的校准因子,计算出点剂量的实测值以及绝对点剂量误差。另外再回顾性地用所有交叉校准因子的平均值重新计算绝对点剂量偏差,并与既有结果进行对比分析。共进行了10批次测量,每批次一个SRT计划。结果显示:用实时交叉校准因子计算出的绝对点剂量偏差均在±3%容差以内,8/10的点剂量误差在±2%以内。而用平均交叉校准因子计算出的结果有2/10超出±3%,仅5/10在±2%以内。用微型电离室进行绝对点剂量测量时,实时交叉校准方法鲁棒性更高。A real-time ion-chamber cross-calibration method was proposed to achieve accurate absolute point dose measurements to plan stereotactic radiotherapy(SRT)for ultra-small volume tumors.The clinical SRT radiotherapy plans were first replicated onto the CT of a stereotactic dose verification phantom with a micro chamber,and the theoretical value of the absolute point dose was calculated via the planning system(TPS).The micro-chamber was then cross-calibrated with a classic farmer chamber prior to each batch of measurements to derive a real-time cross-calibration factor.Finally,measurements were performed with the micro-chamber,and the measured values of the point dose and absolute point dose error were calculated using real-time cross-calibration factors and the calibration factors of the farmer chamber.The absolute point dose errors were then retrospectively recalculated using the average of all cross-calibration factors and compared with the previous results.A total of 10 batches of measurements were carried out,one for each stereotactic body radiation therapy plan.The results showed that the absolute point dose error calculated using the real-time cross-calibration factors were all within±3%tolerance,with 8/10 within±2%.In contrast,2/10 of the results calculated using the average cross-calibration factor exceeded±3%,and only 5/10 were within±2%.The real-time cross-calibration method was found to be more robust when using the micro ion chamber for absolute point dose measurements for ultra-small tumors.

关 键 词：立体定向放疗 超小体积肿瘤 微型电离室 绝对点剂量测量 交叉校准 

分 类 号：R730.55[医药卫生—肿瘤]