Dosimetric Verification of Simulation-Free Palliative Radiotherapy: A Retrospective Study on Delivered Dose Reconstructed on CBCT Setup Images

Abstract

Planning on diagnostic scans may eliminate the need for simulation while reducing wait times for palliative patients. The purpose of this retrospective study is to determine the fidelity of the radiation planned versus delivered in simulation-free palliative radiotherapy (SF-RT).28 palliative patients receiving 31 SF-RT courses underwent planning on diagnostic images from 1/2020 to 11/2020. The actual dose delivered to the patients was reconstructed on the fractional setup CBCT images. Regions receiving 90% and 100% of the original plan's prescription dose were contoured and propagated to the CBCT images registered to the diagnostic images. Changes in the mean dose to those regions (MeanD90% and MeanD100%) were reported as the surrogates for the delivery fidelity, together with the changes in the maximum dose (MaxD), due to the lack of PTV in typical palliative plans. A hypothesis test was performed to determine the significance of the deviations.In all the SF-RT courses, the absolute maximum deviations in the actual delivered dose from the approved plans were 4.1%, 4%, and 3.7% in MaxD, MeanD90%, and MeanD100%, and the mean deviations were 0.07%, 0.35%, and 0.78%, respectively. One-sided one sample t-test were 0.42% (P = 0.66, 95% CI: [-Inf, 0.75%]), 1.51% (P = 0.93, 95% CI: [-Inf, 0.86%]) and 2.56% (P = 0.99, 95% CI: [-Inf, 1.17%]). All deliveries were within a 5% threshold and deemed clinically acceptable.The study quantified the discrepancy between the SF-RT plans and the actual dose delivered for a cohort of patients with palliative intent. The overall deviations were in line with standard palliative RT, which relies on simulation CT images for planning, and deemed clinically acceptable in the palliative setting.