图像引导调强放疗摆位误差对老年前列腺癌患者受照剂量的影响

The impact of set-up errors on dose distribution during the image-guided intensity-modulated radiotherapy in elderly patients with prostate cancer

目的分析摆位误差对肿瘤计划靶体积（PTV）及危及器官受照剂量的影响，探讨前列腺癌调强放疗中摆位误差在线校正的必要性。方法16例前列腺癌患者调强放疗中行治疗机下的锥形束CT（CBCT）扫描共214次，其图像与计划CT图像融合配准获得x、Y、z轴方向平移摆位误差。将上述误差引入治疗计划系统中重新计算得到PTV、膀胱、直肠等的剂量和体积参数并与原计划行配对t检验。结果214次摆位误差再计划的PTV95％体积剂量D95（7613．73cGy比7764．25cGy，t=2．494，P=0．025）和最小剂量Dmin（80．20±9．83比86．80±5．05，t=5．536，P〈0．001）小于原计划，但未超过可接受偏差范围。膀胱接受50Gy剂量体积（V50）和30％膀胱体积剂量（D30）以及直肠接受50Gy剂量体积（V50）和25％直肠体积剂量（D25）与原计划差异不明显。结论平移摆位误差导致PTVD95下降但可接受，膀胱、直肠总体受量变化不明显，前列腺癌放疗过程中在线误差纠正能提高治疗精确性。

Objective To analyze the impact of set-up errors on planning target volume （PTV） for tumors and radiation dose distributions, then to investigate the necessity of on-line set-up error correction for prostate cancer during IMRT. Methods Cone-beam CT （CBCT） scanning images in 16 patients with prostate cancer were acquired with a total of 214 times during IMRT. The CBCT images and the original planning CT images were matched to acquire the translational errors of the x, y and z axis. The dose distributions were recalculated based on the data of each set-up error. The PTV, radiation dose distribution in organs at risk including bladder and rectum, and dose volume parameters were calculated in the re-planning, and then compared with the original planning by paired t-test. Results The PTV 95% dose volume （D95） and PTV minimal dose volume （Dmin） were lower in the re-planning than in the original planning after 214 times set-up （7613.73 cGy w 7764.25 eGy, 80. 2% w 86.8%, t=2. 494 and 5. 536, P=0. 025 or d0. 001）, but it could be acceptable. Bladder received 50 Gy dose volume （V50） ,30% bladder volume dose （D30）, rectume received 50 Gy dose volume （VS0） and 25% rectume volume dose （D25） in the re-planning had no statistical differences with those in the original planning. Conclusions The set-up errors lead to the decrease of PTV D95 but be acceptable. The radiation dose received by bladder and rectum has no obvious changes in the re-planning as compared with the original planning. The on-line set-up error correction for prostate cancer may improve the treatment accuracy during IMRT.