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Implementation of Genetic Algorithm for PTV-Margin in Single Isocenter Multiple Metastases Using Brainlab ElementsTM

J Rojas Lopez1*, R Diaz Moreno2, C Venencia2, (1) Instituto Nacional de Ciencias Medicas y Nutricion Salvador Zubiran, Mexico City, MEXICO (2) Instituto Zunino - Fundacion Marie Curie, Cordoba, ARGENTINA

Presentations

MO-C930-IePD-F7-4 (Monday, 7/11/2022) 9:30 AM - 10:00 AM [Eastern Time (GMT-4)]

Exhibit Hall | Forum 7

Purpose: To optimize PTV margins for single isocenter multiple metastases stereotacticradiosurgery (SIMM-SRS) through a genetic algorithm (GA) that determines the máximum displacement of each target (GTV) due to rotations.

Methods: 10 SIMM-SRS plans were created with Elements Multiple Mets (BrainLab) 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 ± 1.3 cc [0.02, 5.1]. Dosimetrical variations between the original and rotated GTV were evaluated. Then GTV maximum displacement by rotations was obtained using GA. A new PTV margin was optimized based on GTV displacements. The original plans were recalculated using the PTV optimized margin and new dosimetrical variations were obtained. The variations of the mean dose, D99, conformity Padding index (CPI) and gradient index (GI) were studied. The impact of the PTV optimization to the healthy brain was also evaluated. In-house software (MatLab) was developed to perform calculations.

Results: Regarding targets located shorter than 50 mm from the isocenter, the maximum calculated displacement was 2.5 mm. Regarding targets with distances greater than 50 mm, it was 4 mm. The differences between original and rotated GTV were Dmean 1% and for D99, CPI and GI less than 13%. 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). The differences between original and optimized plans for healthy brain were statistically significant for V12 (p = 0.0218) and V10 (p = 0.0264).

Conclusion: The proposed GA allows to determine an optimized PTV margin based on the maximum displacement of the GTV. Optimized margins avoid the detriment of dosimetric parameters and greater margins are associated with an increase in healthy brain volume, which could increase the risk of necrosis.

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