不同锥形束CT图像引导策略对椎体放疗累积剂量的影响

目的:分析不同图像引导放疗(IGRT)策略对椎体放疗累积剂量的影响，探索符合临床要求的图像引导策略。方法:收集椎体转移瘤放疗病例36例，其中常规剂量(PTV 40 Gy分20次)16例，同步推量(PTV 40 Gy分20次，GTV 60 Gy分20次)20例，采用锥形束CT行每日图像引导(DIG)，获取720组分次间摆...

Effect of different cone-beam CT image-guidance strategies on the accumulated dose of radiotherapy for spine metastases

Objective To evaluate the effect of setup errors from daily cone-beam computed tomography (CBCT) on the accumulated dose under different image-guidance (IG) strategies, aiming to investigate the appropriate IG strategies during radiotherapy for the spine metastases. Methods A total of 720 CBCT scans of 36 vertebral lesions were obtained. All 36 lesions were divided into the simultaneous boosting (PTV 40Gy/20f, GTV 60Gy/20f, n=20) and conventional radiotherapy groups (PTV 40Gy/20f, n=16). The actual fractionated plan was recalculated simulatively after transferring the isocenter of the initial plan according to the interfraction setup error. Under no daily image-guidance (no-DIG) strategies including twice imaging guidance weekly (TIG), initial 5 days then weekly imaging guidance (5D+WIG), WIG and no imaging guidance (NIG), the dose deviation was calculated between the delivered dose accumulated by each actual fractionated plan and the dose distribution under DIG. The tolerance of dose deviation for the target was within ±5% and the Dmax of the spinal cord was limited below 45Gy. Results Under different image-guidance strategies of TIG, 5D+WIG, WIG and NIG, the median dose deviation was approximately ±1% for the CTV D95% and Dmax of spinal cord. However, the median dose deviation wasbeyond-5% for the PTV D95% when conventional radiotherapy was given. The median dose deviation was approximately 10% for the Dmax of spinal cord and the proportion of cases whose maximum irradiated dose of spinal cord was more than 4500 cGy was ≥70%. Also, the median dose deviation was beyond -5% for the GTV D95% and PTV D95% when simultaneous boosting was delivered. Conclusions Because the dose deviation of CTVand spinal cord is within the tolerance limit, the image-guidance strategies could be chosen according to the clinical practice when conventional radiotherapy is delivered. However, the dose deviation of spinal cord, GTV and PTV exceeds the tolerance limit under no-DIG strategieswhen simultaneous boosting is delivered. Hence, it is necessary to perform daily IGRT for the spine metastases.