3507 - Clinical Outcomes and Safety of the Combination of External Beam Radiotherapy with <sup>177</sup>Lu-DOTATATE
Presenter(s)
A. Pepin1, J. Eads2, K. A. Cengel3, P. G. Mulugeta4, and N. K. Taunk5; 1Department of Radiation Oncology, Abramson Cancer Center, Hospital of University of Pennsylvania, Philadelphia, PA, 2Division of Hematology and Oncology, University of Pennsylvania, Philadelphia, PA, 3Department of Radiation Oncology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, 4University of Pennsylvania, Philadelphia, PA, 5Department of Radiation Oncology, Hospital of the University of Pennsylvania, Philadelphia, PA
Purpose/Objective(s): Patients with advanced neuroendocrine tumors (NET) who have progression on somatostatin analogue therapy have limited options. The NETTER-1 phase III trial using 177Lu-DOTATATE demonstrated improved progression free survival (PFS) rates in patients with advanced midgut neuroendocrine tumors. It is unknown the practice patterns and safety of the combination of external beam radiotherapy (EBRT) with 177Lu-DOTATATE (PRRT) in the real-world setting. Herein, we characterize the practice, efficacy, and toxicities following a combination of EBRT with PRRT in patients with NETs.
Materials/Methods: All patients treated with PRRT from 2013-2024 were retrospectively extracted from the medical record at a large academic medical center. Patients were stratified into having received EBRT vs no EBRT. Treatment characteristics of both systemic therapy and EBRT were extracted. Toxicities following PRRT and EBRT were assessed. Kaplan-Meier analysis was performed for PFS and overall survival (OS). Simple logistic regression analysis was performed analyzing local control by BED of EBRT.
Results: There were 216 patients analyzed (n=148 PRRT alone, n=68 PRRT+EBRT). Most patients included had a primary neuroendocrine tumor of the small bowel (49.3% PRRT, 23.5% PRRT+EBRT) followed by pancreas (34.5% PRRT alone, 26.5% PRRT+EBRT). Median pretreatment DOTATATE SUVMax were 53.1 and 39 in the PRRT+EBRT vs PRRT alone arms, respectively. Patients were heavily pretreated. Most patients received SSA prior to PRRT (92.6% PRRT+EBRT, 98.6% PRRT alone). The cohort that had EBRT had higher rates of prior chemotherapy (61.8% vs 29.7%, p<0.0001). The cohort without EBRT had higher rates of liver directed therapy (31.8% vs 16.2%, p=0.02). The median 177Lu-DOTATATE activity was 198 mCi for both arms. There was a total of 140 courses of EBRT. Most cases of EBRT were done prior to PRRT (66.4% prior, 6.4% in between cycles, 27.1% after). The use of EBRT prior to PRRT was not associated with receiving fewer cycles of PRRT (p=0.67). The majority of courses of EBRT were to bone (57.9%). The most common side effects following PRRT were fatigue, nausea/vomiting, and cytopenias (e.g., thrombocytopenia, neutropenia, and anemia). There were no significant differences in toxicities between PRRT+EBRT vs PRRT alone, apart from alopecia. There were higher rates of diarrhea (p=0.025) and leukopenia (p=0.032) in patients who received PRRT alone compared to those who had received EBRT within 3 months of PRRT. There were no differences between having received EBRT vs not having received EBRT in PFS (p=0.30) and OS (p=0.81). There were no significant differences between BED in patients who had local control vs did not (p=0.77). On simple logistic regression analysis, the odds ratio was 1.003 (95% CI [0.9858, 1.022], Cox-Snell’s R-squared=0.0007037).
Conclusion: The receipt of external beam radiotherapy in combination with PRRT appears safe. There were no differences in PFS or OS when adding predominantly palliative intent EBRT to PRRT.