ESTRO 2021 Abstract Book

S1260

ESTRO 2021

Results Higher DICE scores were found for the two Plastimatch methods than with Velocity, with smaller organs having lower DICE scores between the propagated and clinician defined contours (see following table). DIR Body Small OARs (<5cc) Large OARs (>5cc) Plastimatch Bspline 0.984±0.002 0.506±0.220 0.829±0.106 Plastimatch Demon 0.976±0.005 0.539±0.216 0.825±0.131 Velocity 0.969±0.005 0.414±0.224 0.782±0.133 On the dosimetric evaluation, variations due to choice of DIR were more pronounced if substantial weight changes occurred, particularly in the parotids. Noticeable differences were also found in homogenous regions of the brain outside of the PTV, where only rigid shifts occurred in reality. However, less uncertainty within the PTV was observed (Fig.2). Moreover, a V dosediff>10% of 28.1% (the volume for which dose differences >10%) was found for accumulated dose in the left parotid (right parotid 13.9%, left retina 9.4%, left macula 8.9%). Fractionation mitigated such uncertainties, but could not eliminate the impact completely.