前列腺癌患者定位与调强放疗时膀胱充盈程度不一致对剂量学参数的影响

目的 分析前列腺癌调强放疗患者治疗与定位时膀胱充盈程度不一致对剂量学参数的影响。方法 42例行调强放疗的前列腺癌患者，真空垫体位固定后行定位CT扫描，用放疗计划系统进行靶区和危及器官勾画、计划设计及计算。患者首次治疗时行锥形束CT（CBCT），与定位CT图像配准后将CBCT图像导入计划系统，将定位CT计划的靶区拷贝至CBCT图像上，并勾画危及器官，采用与定位CT计划相同的计划设计进行剂量计算。比较定位CT计划和CBCT计划获得的剂量学参数差异，包括计划靶区（PTV）平均剂量、均匀性指数（HI）、适形指数（CI）；膀胱及直肠的平均剂量、V₃₀、V₄₀、V₅₀、V₆₀、V₆₅。结果 根据治疗与定位时相比膀胱体积变化，将患者分为膀胱体积缩小组和膀胱体积增大组，42例患者中膀胱体积缩小组有27例，膀胱体积增大组有15例。定位CT计划与CBCT计划比较，下列剂量学参数差异有统计学意义：两组膀胱体积、PTV HI、PTV CI（t=6.838、-4.372、-3.553、-3.462、6.380、5.037，P<0.05）；膀胱体积缩小组膀胱V₃₀、V₄₀、V₅₀、V₆₀、V₆₅（t=-5.004、-4.092、-3.124、-2.707、-2.489，P <0.05）和直肠V₄₀、V₅₀、V₆₀、V₆₅、平均剂量（t=-2.946、-2.643、-2.426、-3.127、-2.530，P <0.05）；膀胱体积增大组膀胱V₃₀、V₄₀、V₅₀及平均剂量（t=5.107、4.204、3.777、4.155，P <0.05）。结论 前列腺癌患者进行调强放疗时，定位和治疗时膀胱充盈程度不一致，会导致靶区及危及器官剂量学参数实际数值与治疗计划计算结果存在差异。

The dosimetric effect of inconsistency of bladder filling states between CT simulation and IMRT treatment for prostate cancer patients

Objective To analyze the dosimetric effect of inconsistent bladder filling states between the CT simulation and treatment for prostate cancer patients undergoing intensity-modulated radiotherapy (IMRT). Methods A total of 42 prostate cancer patients treated with IMRT were selected. After vacuum pad immobilization and simulation CT scan, the delineation of targets and organs-at-risk (OARs), treatment planning and dose calculation were performed on treatment planning system (TPS). The cone-beam-CT (CBCT) acquired before the first treatment was registered to planning CT, on which the target contours were duplicated and OARs were delineated. After dose recalculation on the CBCT using the same plan, the dosimetric differences on the CT and CBCT were compared, including mean dose of the planning target volume (PTV), homogeneity index (HI), conformity index (CI); the mean dose, V₃₀, V₄₀, V₅₀, V₆₀, and V₆₅ of bladder and rectum respectively. Results Relative to the bladder volumes at simulation, the patients were divided into two groups with larger (15 cases) or smaller (27 cases) bladders at the first treatment. Comparing the parameters obtained from simulation CT with that from CBCT, the differences of the following parameters were of statistical significance:the bladder volume, PTV HI, PTV CI in both groups (t=6.838, -4.372, -3.553, -3.462, 6.380, 5.037, P<0.05), the bladder V₃₀, V₄₀, V₅₀, V₆₀, V₆₅ (t=-5.004, -4.092, -3.124, -2.707, -2.489, P <0.05) and rectal V₄₀, V₅₀, V₆₀, V₆₅, mean dose in the group with smaller bladders (t=-2.946, -2.643, -2.426, -3.127, -2.530, P <0.05), and the bladder V₃₀, V₄₀, V₅₀ and mean dose in group with larger bladders (t=5.107, 4.204, 3.777, 4.155, P<0.05). Conclusions For prostate cancer patients undergoing IMRT, the inconsistent bladder filling states between the planning and treatment will cause disimetric differences of targets and OARs.