On the gEUD biological optimization objective for organs at risk in Photon Optimizer of Eclipse treatment planning system

Abstract

Inverse planning optimization using biologically based objectives is becoming part of the intensity modulated optimization process. The performances and efficacy of the biologically based gEUD (generalized Equivalent Uniform Dose) objective implemented in the Photon Optimizer (PO) of Varian Eclipse treatment planning system have been here analyzed. gEUD is associated with the parameter a that accounts for the seriality of a structure, being higher for more serial organs. The PO was used to optimize volumetric modulated arc therapy (VMAT) plans on a virtual homogeneous cylindrical phantom presenting a target and an organ at risk (OAR). The OAR was placed at 4 mm, 1 and 2 cm distance, or cropped at 0, 2 and 4 mm from the target. Homogeneous target dose of 60 Gy in 20 fractions was requested with physical dose‐volume objectives, while OAR dose was minimized with the upper gEUD objective. The gEUD specific a parameter was varied from 0.1 to 40 to assess its impact to OAR sparing and target coverage. Actual head and neck and prostate cases, with one parotid and the rectum as test OAR, were also analyzed to translate the results in the more complex clinical environment. Increasing the a parameter value in the gEUD objective, the optimization achieved lower volumes of the OAR which received the highest dose levels. The maximum dose in the OAR was minimized well with a values up to 20, while further increase of a to 40 did not further improve the result. The OAR mean dose was reduced for the OAR located at 1 and 2 cm distance from the target, enforced with increasing a. For cropped OARs, a mean dose reduction was achieved for a values up to 3–5, but mean dose increased for higher a values. The optimal choice of the parameter a depends on the mutual OAR and target position, and seriality of the organ. Today no significant compendium of clinical and biological specific a and gEUD values are available for a wide range of OARs.

Relativistic Optimization Force Concept for gEUD Biological Optimization and Novel a-value Selection Viewpoint

“…The 0mm-cropped case, reported by Fogliata et. al., 18 is in good agreement with the results of and in this study.…”

Effective optimization strategy for large optimization volume object, remaining volume at risk (RVR): α -value selection and usage from generalized equivalent uniform dose (gEUD) curve deviation perspective

“…Parametric analysis of a-value changes has been widely evaluated (Widesott et al 2008, Mihailidis et al 2010, Lee et al 2012, Teichert et al 2019 as a promising and effective tool for improving the OAR dose. The results obtained in the 0 mm cropped case by Fogliata et al (2018) agree well with the results of this study. The authors concluded that the gEUD relationship to the a-value depends on the DVH shape and that there is no correlation between the gEUD and mean dose.…”

Generalized equivalent uniform dose-based biological optimization in hippocampus-sparing whole-brain radiation therapy

“…However, above a certain value, the D 100% and the D mean values also increased. This was consistent with the phantom study of Fogliata A (2017) [14]. Regarding the hippocampus, the optimal value of the parameter "a" is unknown, so the parameter should be used according to the purpose by predicting the optimized dose based on the characteristics of the serial or the parallel organ.…”