RADT-31. 68GA-DOTATATE PET VERSUS MRI-BASED TREATMENT PLANNING FOR POST-OPERATIVE AND INTACT MENINGIOMA: A DOSIMETRIC ANALYSIS

Abstract Background Nearly all meningiomas express somatostatin receptor 1/2 (SSTR1/SSTR2); therefore, SSTR ligands such as 68Ga-DOTATATE can be utilized for meningioma radiotherapy treatment planning. Incorporation of PET assists with target delineation and may reduce the dose to organs-at-risk (OARs). We hypothesize that PET-based plans will OARs when compared MRI-based plans. METHODS All were rendered on computed tomography (CT) planning datasets, using RapidArc 6MV photon energy. Two arcs positioned coplanar axis alternated collimator settings 0 90 degrees promote MLC sparing a third unique vertex arc chosen independently spare normal brain tissue associated organs at risk (OAR). For MRI structures, 1 cm expansion from gross tumor volume (GTV) created clinical (CTV)60. A 2 CTV54. GTV CTV60. 3 mm isotropic volumes (PTVs). Plans optimized Dmax brainstem remained limited 60Gy or less optic structures was 54Gy less. RESULTS 18 patients included (9 post-operative, 9 intact). The mean PTV 258 ccs (306 210 intact), 60 (97 91 radiation both nerves, chiasm, hippocampi, reduced favoring post-operative intact patients. CONCLUSION Our study shows incorporation patients, this difference translate toxicity. guided treatments are worthy future prospective investigation.