胰腺癌立体定向体部放疗摆位误差对靶区乏氧区的同步推量研究

目的 分析胰腺癌立体定向体部放射治疗（SBRT）乏氧区的同步推量（SIB）对靶区和危及器官的影响，预测肿瘤内部乏氧区的最佳推量。方法 回顾性分析10例胰腺癌SBRT患者治疗前后分别获取的共100组锥形束CT（CBCT）校正数据，导入计划系统重新计算靶区和危及器官剂量。引入两种肿瘤控制率（TCP）模型计算不同乏氧状态下的肿瘤控制率，找出肿瘤控制率与靶区剂量的关系。结果 治疗前摆位误差引起的计划靶区（PTV）和内靶区（ITV）的靶区覆盖率平均值分别下降8.9%和9.2%，治疗过程中摆位误差引起的PTV和ITV靶区覆盖率的平均值分别下降1.6%和1.3%。所有计划中危及器官剂量偏差的平均值在-0.11~0.26 Gy之间。氧增强比（OER）为1、1.5和3时，乏氧区同步推量的平均剂量（D_mean）预测值分别为31.4、34.0和37.2 Gy（Niemierko模型）或31.6、33.9和37.2 Gy（Poisson模型）。结论 经过CBCT校正以后，治疗过程中的误差对靶区覆盖率和危及器官的影响可忽略。不考虑肿瘤乏氧问题会极大影响肿瘤控制率的计算。为消除乏氧对肿瘤控制的影响，胰腺癌乏氧区（OER=3）的D_mean应至少为处方剂量的1.24倍。

Simultaneous integrated boost on hypoxic region by means of setup errors for pancreatic cancer SBRT

Objective To assess the dosimetric impact on the target volumes and organs at risk (OARs) using simultaneous integrated boost (SIB) for the hypoxic regions of the pancreatic cancer patients treated with stereotactic body radiotherapy (SBRT), and to predict an optimal way of SIB. Methods The setup corrections guided by 100 sets of CBCT scans of 10 patients previously treated with SBRT were imported to the treatment planning system (TPS) to recalculate the dose to the target and OARs. Two tumor control probability (TCP) models were applied to calculate the TCP under various hypoxic situations. The correlations between the TCP and target dose were analyzed.Results Without setup corrections, the PTV and ITV were underdosed by 8.9% and 9.2% on average respectively relative to planed dose. With setup corrections, the mean dose to PTV and ITV coverage were 1.6% and 1.3% lower than planned respectively. The mean deviations of OAR dose were between -0.11 Gy and 0.26 Gy for all plans. The predictive values of D_mean on hypoxic regions were 31.4, 34.0 and 37.2 Gy (Niemierko model) or 31.6, 33.9 and 37.2 Gy (Poisson model) when the oxygen enhancement ratios (OERs) were 1, 1.5 and 3 respectively.Conclusions With CBCT setup corrections, the dosimetric impacts of setup errors on the target and OARs can be neglected. Significant deviations of TCP calculation were observed without accounting for tumor hypoxia. To counteract the impacts of hypoxia, the mean dose to the hypoxic regions should be at least 1.24 times of prescribed dose.