ESTRO 2022 - Abstract Book

S712

Abstract book

ESTRO 2022

isolate the difference between applying the two types of uncertainties. The proton plans were re-calculated after applying range uncertainties that were either TS (different range uncertainties for lung, soft, and bone tissues, as categorized by the CT number of the specific voxel) or fixed TI (0.5%-5.0%). The re-calculated proton plans were compared based on dose volume histogram (DVH) parameters for the target, ring structures around the target, and organs-at-risk (OARs). For each treatment site, the optimal TI range uncertainty was defined as the one resulting in the largest overlap between the TS and TI DVH values.

Results The range uncertainties were found to be 8.0% of the proton range for lung, 1.0% for soft, and 2.3% for bone tissues. When comparing the re-calculated proton plans, dose differences were mainly found in the vicinity of the target. It was found that a single TI uncertainty did not provide the best fit for all DVH parameters in any of the treatment sites (Fig 2). Hence, the differences between the two types of re-calculated proton plans were smallest when several TI range uncertainties were used for each treatment site. However, the differences between the DVH values found using TS and TI range uncertainties increased only slightly when using a single TI uncertainty for all DVH parameters for each treatment site. The single best-fitting TI uncertainty was found to be 1.0% for the pelvic and HN patient, 1.5% for the liver patient, and 2.0% for the thorax phantom.