Use of genetic algorithm for PTV optimization in single isocenter multiple metastases radiosurgery treatments with Brainlab Elements™.

Abstract

To optimize PTV margins for single isocenter multiple metastases stereotactic radiosurgery through a genetic algorithm (GA) that determines the maximum effective displacement of each target (GTV) due to rotations. 10 plans were optimized. The plans were created with Elements Multiple Mets™ (Brainlab AG, Munchen, Germany) from a predefined template. The mean number of metastases per plan was 5±2 [3,9] and the mean volume of GTV was 1.1±1.3cc [0.02, 5.1]. PTV margin criterion was based on GTV-isocenter distance and target dimensions. The effective displacement to perform specific rotational combination (roll, pitch, yaw) was optimized by GA. The original plans were re-calculated using the PTV optimized margin and new dosimetric variations were obtained. The Dmean, D99, Paddick conformity index (PCI), gradient index (GI) and dose variations in healthy brain were studied. Regarding targets located shorter than 50mm from the isocenter, the maximum calculated displacement was 2.5mm. The differences between both PTV margin criteria were statistically significant for Dmean (p=0.0163), D99 (p=0.0439), PCI (p=0.0242), GI (p=0.0160) and for healthy brain V12 (p=0.0218) and V10 (p=0.0264). The GA allows to determine an optimized PTV margin based on the maximum displacement. Optimized PTV margins reduce the detriment of dosimetric parameters. Greater PTV margins are associated with an increase in healthy brain volume.