The Effect of Cone-Beam CT Image-Guidance Strategies on the Delivered Dose for Spine Metastases Radiotherapy

Purpose/Objective(s) This article will investigate the appropriate image-guidance (IG) strategy for spine metastases (SpM) radiotherapy by analyzing the delivered dose under different IG strategies with setup errors from daily cone-beam computed tomography (CBCT). Materials/Methods A total of 720 CBCT scans about 36 vertebrae lesions from 2017 to 2019 were enrolled. All lesions were divided into two groups, twenty for simultaneous boost (PTV 40 Gy/20f, GTV 60 Gy/20f) and sixteen for conventional fractionated (PTV 40 Gy/20f). The actual fractionated plan was recalculated after transferring the isocenter of the original plan according to the inter-fraction setup error. Then under no daily image-guidance (no-DIG) strategies, like twice imaging guidance weekly (TIG), initial 5 days then weekly imaging guidance (5D+WIG), weekly imaging guidance (WIG) and no imaging guidance (NIG), the dose deviation was calculated between the delivered dose accumulated by each actual fractionated plan and the original RT-plan which is regarded as the dose distribution under daily image guidance (DIG). The tolerance of dose deviation for the target is within ± 5% and the Dmax of the spinal cord is limited below 45 Gy. Results When conventional fractionated radiotherapy, under strategies of image-guidance like TIG, 5D+WIG, WIG and NIG, the median dose deviations are 0% (-1.0% ∼ 1.2%), 0.2% (-0.8% ∼ 1.2%), 0.4% (-0.6% ∼ 1.8%), 0.8% (-0.2% ∼ 2.4%) for the Dmax of spinal cord; -0.2% (-1.4% ∼ 0%), -0.4% (-1.4% ∼ 0%), -0.8% (-2.3% ∼ -0.4%), -1.6% (-3.2% ∼ -0.8%) for the CTV D95; -6.0% (-8.4% ∼ -4.6%), -5.9% (-8.3% ∼ -4.6%), -8.0% (-11.3% ∼ -6.4%), -10.8% (-14.4% ∼ -8.7%) for the PTV D95. When simultaneous boosting, the median dose deviations correspondingly are 9.5% (7.2% ∼ 12.4%), 9.3% (7.0% ∼ 11.9%), 11.2% (9.3% ∼ 16.4%), 14.2% (11.6% ∼ 20.2%) and the proportions of case whose maximum irradiated dose of spinal cord is more than 45 Gy are all beyond 70% for the Dmax of spinal cord; -5.1% (-7.9% ∼ -4.2%), -4.7% (-7.4% ∼ -4.2%), -7.0% (-10.3% ∼ -6.0%), -8.6% (-13.1% ∼ -7.3%) for the GTV D95; -3.5% (-7.3% ∼ -2.1%), -3.4% (-6.8% ∼ -1.7%), -6.2% (-11.1% ∼ -3.9%), -9.0% (-16.5% ∼ -5.6%) for the PTV D95. Conclusion When conventional fractionated radiotherapy, the image-guidance strategies could be chosen according to the clinical practice. However, it is necessary to do daily IGRT for spine metastases radiotherapy when simultaneous boosting because the dose deviations for the Dmax of spinal cord, GTV D95 are all out of the tolerance. Author Disclosure C.Jia: None. B. Zhao: None. X. Gao: None. Y. Bai: None. Z. Shang: None.