食管癌调强放疗中摆位误差对剂量学的影响

Impact of setup errors on dose distribution of intensity modulated radiotherapy for patients with esophageal carcinoma

目的通过电子射野影像装置（EPID）测量食管癌患者在调强放疗过程中的摆位误差,分析摆位误差对靶区和正常组织受量的影响,验证目前计划靶体积（PTV）外放范围的合理性。方法 36例食管癌患者用EPID测量其摆位误差,每位患者接受摆位验证4-6次（1次/周）。在医科达（CMS-XIO）治疗计划系统上模拟实际摆位误差,比较实际治疗过程中大体肿瘤体积（GTV）、临床靶区体积（CTV）和周围正常组织的受照剂量。结果 36例食管癌患者前后、左右、头脚方向摆位误差分别为（2.43±1.80）、（2.56±1.87）和（3.53±2.82）mm。摆位误差使食管癌患者GTV的95%体积接受的剂量（D95）与原治疗计划相比降低了50 c Gy,CTV的D95降低了78.21 c Gy。原计划（P1）和摆位误差计划（P2）的全肺接受20 Gy照射体积占全肺体积的百分比（V20）分别为24.34%和23.52%（P〈0.05）;心脏平均剂量分别为2 067.23 c Gy和2 021.33 c Gy（P〈0.05）;P1中无一例脊髓受量超过4 500 c Gy,而P2中12例脊髓最大剂量超过4 500 c Gy,其中1例最大剂量为5 602.70 c Gy。结论摆位误差使GTV、CTV的受照剂量降低,部分患者脊髓最大剂量超过耐受量,双肺、心脏受照剂量有所下降。

Objective To measure the setup errors in patients with esophageal carcinoma during the treatment of intensity modulated radiotherapy（ IMRT） by electronic portal imaging device（ EPID）,so as to analyze the impact of setup errors on dose distribution of target volume and normal tissues around and verify the rationality on expanding margin of the planning target volume. Methods The setup errors of 36 patients with esophageal cancer were measured once a week for 6 times by EPID. The setup errors were integrated into the XIO treatment planning system by moving the isocenter,and then the dose distribution of GTV,CTV and normal tissues were recalculated. Results The setup errors of the 36 patients in the direction of Z-,X- and Y-axis were 2. 43 ± 1. 80,2. 56 ±1. 87 and 3. 53 ± 2. 82 mm,respectively. The dose covered 95% GTV（ D95） was reduced by 50 c Gy,and CTV D95 by 78. 21 c Gy. The lung V20 in the original plan and the integrated plan was 24. 34% and 23. 52%,respectively（ P〈0. 05）. The average dose of the heart in the two plans was 2 067. 23 and 2 021. 23 c Gy,respectively（ P〈0. 05）. In the original plan,no patient had maximum dose of spinal cord over 4 500 c Gy. While in the integrated plan there were 12 patients with the spinal cord dose more than 4 500 c Gy,with a maximum dose of 5 602. 70 c Gy. Conclusion The setup errors cause significant dose reduction of GTV and CTV; the maximum dose of the spinal cord in some patients exceeds 4 500 c Gy,but the dose of the lung and the heart decreases due to the setup errors.