锥形束CT测量胸段食管癌调强放疗摆位误差对剂量学的影响

目的 应用千伏级锥形束CT(kV-CBCT)测量胸段食管癌调强放疗的摆位误差,探讨摆位误差对肿瘤靶体积和周围正常组织受照剂量的影响.方法 21例胸段食管癌患者经图像引导调强放疗,共获得173组CBCT摆位误差数据,利用这些数据在三维治疗计划系统中模拟患者的实际治疗过程,分析摆位误差对肿瘤靶区及周围正常组织受照剂量的影响.结果 21例患者左右、头脚、前后方向的摆位误差分别是(2.73 ±1.85)、(3.19±2.71)和(2.35±1.71)mm.摆位误差对患者GTV的剂量学影响不明显,但误差却使患者95％ PTV( D95％)接受的剂量与标准计划相比降低3.38 Gy,PTV最小剂量(Dmin)和平均剂量(Dmean)分别下降9.83和0.65 Gy,摆位误差的修正提高了计划靶区的适形度和剂量均匀性,标准计划相应值分别为(0.74±0.10)和(1.07±0.02),模拟计划相应值分别为(0.69±0.08)和(1.13±0.07),差异均有统计学意义(t=3.43和-3.91,P＜0.05)；摆位误差对脊髓的最大剂量(Dmax)、双肺和心脏等周围正常组织受照剂量影响,差异无统计学意义(P＞0.05),模拟计划中脊髓的最大剂量均值为(42.20±4.97)Gy,标准计划为(41.37±2.75) Gy,摆位误差使部分患者脊髓最大剂量超过45 Gy,其中1例最大值达到52.8 Gy.结论 kV-CBCT图像引导胸段食管癌调强放疗可减小患者的摆位误差,提高PTV的受照剂量和治疗精度,摆位误差对双肺、脊髓和心脏受照剂量未见明显改变.

A kV cone-beam CT based analysis of the setup errors and the corresponding impact on the dose distribution of intensity modulated radiotherapy for thoracic esophageal carcinoma

Objective To measure the setup errors in thoracic esophageal carcinoma treated with intensity modulated radiotherapy (IMRT) using kilo-voltage cone-beam CT (kV-CBCT), and to evaluate the impact of the setup errors on the dose distributions in tumor target volume and the peripheral normal tissues.Methods Twenty-one patients with thoracic esophageal carcinoma undergoing image guided IMRT (IG-IMRT) were included in this study. Using kV-CBCT, 173 setup errors of these patients were acquired before treatment. By shifting the isocenters, these setup errors were simulated in the 3-dimentional treatment planning system and the corresponding impact of the dose distribution in tumor target volume and peripheral organs were evaluated. Results The translational deviations of lateral, longitudinal and vertical directions were (2.73±1.85), (3.19±2.71), and (2.35±1.71)mm, respectively. The dose of gross tumor volume (GTV) was not impacted significantly by the setup errors. However, comparing with the standard plan without setup errors, the setup errors in the simulated plan reduced the dose of 95% planning target volume (PTV) by 3.38 Gy. The dose to PTV D_min and PTV D_mean were also reduced by 9.83 Gy and 0.65 Gy respectively. The correction of setup errors improved the conformity index (CI) and the homogeneity index (HI) for PTV. The CI and HI for the standard plan were 0.74±0.10 and 1.07±0.02, respectively. The CI and HI for the simulated plan were 0.69±0.08 and 1.13±0.07, respectively. Statistically significance was observed in these differences (t=3.43 and -3.91 respectively, P<0.05). No statistical significance was observed in the dose differences in lungs, spinal cord and heart between the two plans (P>0.05). The mean maximum dose of the spinal cord was (42.20±4.97)Gy in the simulation plan, which was (41.37±2.75)Gy in the standard plan. For some patients, the maximum dose of the spinal cord exceeded the tolerance level of 45 Gy in the simulation plan, and one case even reached 52.8 Gy. Conclusions Using the image guidance of kV-CBCT, the setup errors can be reduced significantly for patients with esophageal carcinoma receiving IG-IMRT. The correction of setup errors can increase the treatment precision and enhance the dose in PTV. No significant dose changes were observed in the lung, spinal cord and heart as a result of setup error correctio.