External beam radiation therapy for advanced/unresectable malignant paraganglioma and pheochromocytoma

Purpose/Objectives To evaluate the role of external beam radiation therapy (EBRT) for treatment of malignant paraganglioma (PGL) and pheochromocytoma (PCC). Methods and materials A retrospective review was performed of all patients with malignant PGL/PCC treated with EBRT at our institution between 1973 and 2015. Local control (LC) per treated lesion and overall survival were estimated using the Kaplan-Meier method. Toxicities were scored using the Common Toxicity Criteria for Adverse Events (AE), version 4. Results The cohort included 41 patients with 107 sites treated. Median (range) age at EBRT was 33 (11-80) years. Treatment intention was curative in 20 patients (30 lesions) and palliative in 21 patients (77 lesions). The primary tumor was PGL (63%) and PCC (37%). Previous local therapies were surgical resection (90%) and percutaneous ablation (19%). Indications for EBRT were local control (66%), pain (22%), or spinal cord compression (12%). Treatment site included bone (69%), soft tissue (30%), and liver (1%). Median (range) EBRT dose was 40 (6.5-70) Gy. Median biologic effective dose using α/β = 10 (BED₁₀) was 53 (9-132). Median follow-up was 3.8 years (0.04-41.5), and mean follow-up was 9.7 years. Overall survival at 5 years was 65%: 79% for curative- and 50% for palliative-intention patients (P =.028). LC at 5 years was 81% for all lesions; 91% for lesions receiving BED₁₀ ≥53, and 62% for lesions receiving BED₁₀ <53 (P =.001). All 11 lesions treated with stereotactic body RT or radiosurgery had LC at a median of 3.0 (0.2-5.4) years. For the symptomatic lesions, symptoms improved in 94%. There were no acute grade ≥3 treatment-related AEs, including no hypertensive crises. Two patients developed a late grade ≥3 AE. Conclusions EBRT is a useful treatment modality for malignant PGL and PCC. Higher RT dose was associated with improved LC.