鼻咽癌调强放疗中摆位误差对物理剂量学的影响

目的：测量头颈部肿瘤在放射治疗中的摆位误差，分析鼻咽癌（NPC）调强放射治疗（IMRT）中误差对靶区和危及器官物理剂量学的影响。方法：随机抽取76名头颈部肿瘤患者，通过比较数字重建图像（DRR）和射野图像，测量其摆位误差；从其他住院患者中随机抽取另外10名作调强治疗的鼻咽癌患者，在计划系统中模拟患者治疗时体位的三维误差，重新计算剂量分布，分析一系列相关的靶区和危及器官的剂量参数，明确摆位误差对物理剂量的影响。结果：头颈部肿瘤在左右、头脚、腹背方向的摆位误差分别是（-0．62±1．46）mm，（-0．41±1．54）mm，（-0．31±1．67）mm；鼻咽癌调强放疗中超过3mm的摆位误差对GTV的最小剂量和CTV个别剂量参数的影响有统计学意义，腹背方向的误差对脊髓和脑干受照剂量的影响有统计学意义。结论：对于鼻咽癌调强治疗的患者，摆位误差需要控制在3mm之内：在日常工作中用EPID做质量保证和质量控制工作很有必要。

Effects of the Setup Error on the Physics Dose for Nasopharyngeal Carcinoma Undergoing the Intensity Modulated Radiation Therapy

Objective： To measure the setup error undergoing the radiation therapy for head-neck neoplasms, and to analyze the effect of the setup error on the physics dose of targets and peripheral organs at risk （OAR）for nasopharyngeal carcinoma （NPC）undergoing the intensity modulated radiation therapy （IMRT）. Methods： Seventy-six patients with head-neck neoplasms were choosed at random, measured the setup errors through comparing their digital portal films with their digitally reconstructed radiographs （DRR）. Other ten NPC patients in hospital were choosed, simulated the patients＇ three-dimensional errors in actual therapy on the treat planning system （TPS）, and recalculated their dose distribution. We analyzed a series of relative targets and OAR dose parameters, obtained the impact of the setup errors on the physics dose. Results： The setup errors were （-0.62±1.46） ram,（-0.41 ±1.54） mm and（-0.31 ±1.67） mm in left-right, cranial-caudal and ventral-dorsal directions respectively. If the setup errors exceed 3 ram,they have statistics signification （P〈0.05） for GTV in low dose, few parameters in CTV, and spinal cord and brainstem in ventral-dorsal direction. Conclusions： For the patients with NPC undergoing the IMRT, the setup errors should be controlled within 3 mm. So in the daily work, a series of strict QA and QC work through EPID（electronic portal imaging device） is very important.