ESTRO 2024 - Abstract Book

S4729

Physics - Optimisation, algorithms and applications for ion beam treatment planning

ESTR0 2024

achieving full plan optimization for the case with twelve metastases within less than 10 min. SPArc, SHArc( 4 He) and SHArc( 12 C) multi-met SISRS was evaluated for patient cases with three to twelve metastases (target volumes between 0.03 cm 3 and 20 cm 3 ) publicly available through Varian (Palo Alto, CA, USA). PTVs extended GTVs by an isotropic 1 mm margin, and robust optimization with 1 mm/2.5 % criteria was applied. For biological dose optimization, both clinical (LEM I) and state-of-the-art relative biological effectiveness (RBE) models (mMKM, LEM IV) were employed. For comparison, we generated hyperArc VMAT (HA-VMAT) plans for the patients on the PTVs using the Varian Eclipse treatment planning platform.

Results:

Figure 1: SHArc, SPArc, HA-VMAT for a case with three (left) and twelve lesions (right). Biological dose optimization for SHArc utilized different RBE models: The modified microdosimetric kinetic model (mMKM) for SHArc plans on the left, and RBE = 1.1 for SPArc and LEM I for SHArc( 12 C) on the right. Figure 1(left) shows a comparison between HA-VMAT, SHArc( 4 He) and SHArc( 12 C) for a case with three metastases. Figure 1(right) compares HA-VMAT, SPArc and SHArc( 12 C) for a case with twelve lesions. Dose volume histograms are shown below the dose distributions. Both SHArc and SPArc plans were comparable and highly conformal to the PTV. Particle arc plans indicated a substantial reduction in the low-dose bath, while intermediate doses to the brain were similar for the cases with up to five lesions or slightly increased for the case with twelve lesions. This can likely be attributed to the robust optimization settings, which result in an extension of the mid-dose region beyond the PTV. These were chosen conservative with respect to the advances in range accuracy brought forward by Dual-Energy CT [3].