RADT-06. SPARING OF MOTOR STRUCTURES IN ADJUVANT RADIATION THERAPY AFTER RESECTION OF BRAIN METASTASES: APPLICATION OF NTMS-DERIVED DTI-BASED MOTOR FIBER TRACKING IN ADJUVANT STEREOTACTIC RT TREATMENT PLANNING

Abstract

Abstract BACKGROUND Resection of brain metastases (BM) close to the motor cortex and the corticospinal tract (CST) bears a significant risk for treatment-related morbidity. Navigated transcranial mapping (nTMS) combined with diffusion-tensor-imaging (DTI) based fiber tracking (DTI-FTTMS) is a valuable tool to guide the neurosurgeon along the CST to preserve motor function. This study aims to proof the practicability of DTI-FTTMS in local adjuvant stereotactic RT planning in the management of BM. Method: Pre-surgical generated DTI-FTTMS-based CST reconstructions of 24 patients with 25 resected BM were incorporated into the RT planning system and elastic fused with planning imaging. The CST was delineated as the planning risk volume (PRV-FTTMS). Fractionated stereotactic intensity-modulated RT (IMRT) plans (7 x 5 Gy) were retrospectively calculated and then optimized to preserve PRV-FTTMS. Areas covered by the planning target volume (PTV) were not spared (overlap). RESULTS In regular plans mean dose (Dmean) of complete PRV-FTTMS was 5.4 ± 2.5 Gy. Regarding PRV-FTTMS portions within the 8.75 Gy (25% of prescription dose) isodose level Dmean was 18.2 ± 4.3 Gy and after plan optimization 13.1 ± 3.8Gy (-28.0%, p < 0.001). Within the 17.5 Gy (50%) isodose line PRV-FTTMS Dmean was reduced by 31.7% from 24.3 ± 3 Gy to 16.6 ± 4.8 Gy (p< 0.001). There was no decline of the effective treatment dose, PTV Dmean in regular plans was 36.9 ± 0.7 Gy vs. 37.7 ± 1.4Gy (p=0.013) after adaption. PTV coverage (V35Gy(%)*100) did not change with plan optimization: 0.99 vs. 0.99 (p=0.43). Dose constraints of organs at risk were all met both in regular and optimized plans. CONCLUSION DTI-FTTMS based motor tracts could be implemented in the adjuvant stereotactic RT planning of cavities after resection of BM. A significant dose reduction of motor structures within critical dose levels seems possible without reducing PTV treatment dose. However, the functional benefit needs to be investigated prospectively within clinical trials.