ABSTRACT
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 40 Gy/20f, GTV 60 Gy/20f, n=20) and conventional radiotherapy groups (PTV 40 Gy/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 D max of the spinal cord was limited below 45 Gy. Results:Under different image-guidance strategies of TIG, 5D+ WIG, WIG and NIG, the median dose deviation was approximately ±1% for the CTV D 95% and D max of spinal cord. However, the median dose deviation was beyond -5% for the PTV D 95% when conventional radiotherapy was given. The median dose deviation was approximately 10% for the D max 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 D 95% and PTV D 95% when simultaneous boosting was delivered. Conclusions:Because the dose deviation of CTV and 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 strategies when simultaneous boosting is delivered. Hence, it is necessary to perform daily IGRT for the spine metastases.