RADT-41. RADIOSURGERY FOR GLOMUS TUMORS: IMPACT OF MRI-PET FUSION ON TREATMENT PLANNING AND OUTCOMES

Abstract Paragangliomas present a challenge for stereotactic radiosurgery (SRS) treatment planning, particularly regarding the delineation of tumor boundaries. We propose that integrating 68Ga-DOTATATE PET scans alongside MRI in SRS planning will facilitate superior target identification and tumor coverage compared to reliance on MRI alone. A retrospective analysis of 9 patients diagnosed with paraganglioma who underwent MRI and 68Ga-DOTATATE PET imaging over a 20-month period was conducted. Images were imported into GammaPlan treatment planning software, partitioned into separate sessions: one with MRI and another with MRI-PET fusion. A single evaluator contoured paragangliomas as gross tumor volume (GTV) initially using MRI alone and subsequently with PET/MRI fusion. The pre- and post-PET fusion GTV volumes were compared. The standard deviation of the percentage increases in volume was calculated to assess variability across the sample. Of included 9 patients, 7 were females and median age was 58.3 years. Four patients had prior surgery. Seven patients were treated with Gamma Knife, while 2 with LINAC. Two patients were treated with single fraction SRS while 7 with hypofractionated SRS. Across all treated patients (n=9), GTV volumes significantly increased with PET fusion, with an average volume increase of 26.02% (n=8). One patient reported dryness of throat after SRS. Significant PET avidity over structures like temporal bone, internal jugular vein, petrous internal carotid artery and sigmoid sinus-IJV junction were included in PET/MRI fusion GTVs, which were missed on isolated MRI contours. At median 6-month follow up, all patients had a stable radiological response. Integration of 68Ga-DOTATATE PET scans with MRI enhances the visualization of paragangliomas in patients undergoing SRS. Further extensive studies are warranted to validate this observation and to better understand the variability in treatment response observed across the patient population. Our practice has initiated routine utilization of DOTATATE-PET imaging in paraganglioma patients undergoing SRS planning.