Standardising image registration and dose mapping for thoracic reirradiation: A national multi-centre benchmarking study

Background and purposeSafe delivery of high-dose reirradiation depends on robust evaluation of previously delivered dose on current patient anatomy. This study aims to assess the variability of 1) rigid (RIR) and deformable (DIR) image registration and 2) dose-mapping based on RIR or DIR, as part of the pre-trial quality assurance for CURE Lung, a Scandinavian thoracic reirradiation trial. Materials and methodsSeven lung cancer cases, treated with curatively intended reirradiation near a previously irradiated region, were distributed to six Danish centres. Organs-at-risk (OARs) were delineated on CT images of previous (CTprev) and current treatment (CTcurrent). RIR and DIR from CTprev to CTcurrent were performed for all cases at each centre, and doses were mapped from CTprev to CTcurrent using both methods. Mapped and current physical doses were converted to equieffective doses (EQD2), and cumulative EQD2-doses were generated on CTcurrent. Inter-centre variation was assessed using volume coefficients and distance measurements. A linear mixed-effects model tested the effect of registration method on OAR alignment, near-maximum and volumetric EQD2-dose constraints from CURE Lung, and variability in DVH bands.ResultsDIR significantly reduced the geometrical variations for all OARs, with mean surface distances