头颈部肿瘤摆位误差对调强放疗计划的影响

目的研究头颈部肿瘤患者调强放疗分次间摆位误差对患者所接受的放射剂量的影响。方法在患者治疗前利用机载千伏级锥形束CT（KV—CBCT）进行扫描，在XVI软件里自动将CBCT图像和计划cT图像进行配准得到平移和旋转误差。在Pinnacle治疗计划系统中把平移和旋转误差模拟出来，然后重新计算剂量，将得到新的剂量分布和原计划进行比较、分析。评价指标包括原发肿瘤计划靶区（GTV—T．P）的平均剂量（Dm）、包含95％体积的剂量（D95）；脑干1％体积的剂量（D1％）及1cc的剂量；脊髓1％体积的剂量（D1％）及1cc的剂量；双侧腮腺的平均剂量及接受超过30Gy剂量的体积（V30）。应用SPSS16．0软件进行统计分析。结果头颈部肿瘤分次间沿X、Y、Z轴的平移误差和旋转误差分别为（1．02±0．83）、（1．28±1．08）、（1．27±1．06）mm和（0．79±0．67）°、（1．00±O．82）°、（0．73±0．68）°。患者脑干、脊髓、腮腺受量变化差异有统计学意义，原发肿瘤计划靶区平均受量差异无统计学意义，其D95统计结果有明显差异，但其平均变化率仅为2．18％。结论调强放疗中摆位误差无论对靶区还是正常组织的剂量分布都产生影响，而正常组织的剂量和靶区相比受摆位误差的影响更大。

The impact of setup errors on treating head and neck cancer with intensity modulated radiation therapy

Objective To study the impact of setup errors on treating head and neck cancer （HNC） with intensity modulated radiation therapy （IMRT）. Methods Patients were scanned with KV-CBCT to adjust position before treatment. The setup errors including translational errors and rotation errors were gain from XVI （X-Ray volume Image） matched with original planed CT image. The setup errors were input to pinnacle treatment planning system, and then the treatment plans with setup errors were re- ealeulated. The dose distribution and dose volume histogram （DVH） of tumor and critical structure were compared with original treatment plan. The evaluation indicators included mean dose （Din） of planning target volume of primary tumor （ GTV-T-P）, dose of 95% volume （D95） ,dose of 1% volume and lcc volume of spinal cord and brainstem, mean dose of bilateral parotid gland and the dose volume received more than 30Gy. Statistical analysis was perfonned by using SPSS 16. 0. Results The mean transational error and rotation error along X,Y and Z axis were （ 1.02 ±0. 83） mm, （ 1.28 ±1.08） mm and （ 1.27 ± 1.06） mm respectively, and （0. 79 ± 0. 67 ） degree, （ 1. 00 ±0. 82 ） degree and （0. 73± 0. 68 ） degree respectively. The dose differences among brainstem,spinal cord and parotid gland were statistically significant. The difference of GTV-T-P （Din） was not statistically significant ,while D95 was significant different but the average rate of change was 2. 18% only. Conclusion Setup error of IMRT affect dose distribution of both target and normal tissue ,and the effect is greater on normal tissue than that on target lissue.