Overlap-guided fixed-patient support positioning optimization for cranial SRT.

Abstract

To investigate potential dosimetric improvements through the optimization of fixed-couch rotational position in cranial cancer stereotactic treatments. Using previously delivered cranial stereotactic radiotherapy plans treated at the Nova Scotia Health Authority (NSHA), we have redesigned the treatment arrangement to find the optimal couch rotation positions based on the reduction of overlap between organs-at-risk of exposure (OARs) and target volume (PTV). Maintaining the gantry arrangements from the delivered treatment, the couch positions were determined based on a cost function analysis of accumulation of overlap score from an equationdeveloped by Yang etal. and refined by MacDonald etal. The algorithm incorporates factors for radiation dose sensitivities of each OAR, depth of both OARs and target (PTV) volumes, and orthogonality of the 3D vector between OAR and PTV in the case of proximal OAR position. The plan evaluation was conducted on 16 acoustic neuroma patients treated with stereotactic radiotherapy plans at the NSHA. Maximum and mean doses to the OARs were reduced by approximately 14.30%±2.86% and 19.25%±2.10%, respectively, with application of this optimization technique as compared to the delivered treatment plans. In addition, PTV conformity and homogeneity were improved with application of this optimization technique. This variation of the existing delivery techniques with guidance from a PTV-OAR overlap cost function analysis technique can yield significant dosimetric improvements with no increase to delivery or planning time.