3511 - Combining Lu177-PSMA and External Beam Radiation Therapy: A Retrospective Safety Analysis
Presenter(s)
D. Rafizadeh1, S. Dwabe2, O. Yazdanpanah2, D. Kaakour2, S. Feinstein3, A. Rezazadeh4, N. Mar5, and S. N. Seyedin6,7; 1University of California, Irvine, School of Medicine, Irvine, CA, 2University of California, Irvine, Division of Hematology/Oncology, Orange, CA, 3University of California, Irvine, Department of Radiation Oncology, Orange, CA, 4Division of Hematology/Oncology, Department of Medicine, UC Irvine School Of Medicine, Orange, CA, 5UC Irvine School Of Medicine, Division of Hematology/Oncology, Department of Medicine, Orange, CA, 6Department of Radiation Oncology, University of California - Irvine, Orange, CA, 7University of California, San Francisco, Department of Radiation Oncology, San Francisco, CA
Purpose/Objective(s): 177Lu-PSMA-617 (Lu177-PSMA) delivers internal radiation therapy to those with metastatic castrate resistant prostate cancer. External beam radiation therapy (EBRT) is utilized regularly for prostate cancer metastases symptom relief. The primary goal of this study was to identify treatment-related adverse events (TRAEs) following the completion of both Lu177-PSMA and EBRT.
Materials/Methods: This single-institution retrospective study selected patients with metastatic prostate cancer who underwent at least 1 cycle of Lu177-PSMA and initiated EBRT to any site, at any point in their treatment. Patient characteristics, EBRT dose, location of irradiated sites, sequence and timing of co-administration, number of Lu177-PSMA cycles and dose administered, concurrent therapies, severity/type of radiation TRAEs, and symptom relief after EBRT and dual treatment were recorded. Treatment toxicity after both modalities was classified utilizing the common terminology criteria for adverse events (CTCAE) version 5.0. Acute toxicity and chronic toxicities were defined as occurring within or greater than 90 days following the completion of both treatments, respectively. In addition, symptom relief was characterized as none, minimal, significant, or complete.
Results: With a median age of 75, eleven patients with 34 irritated sites met eligibility criteria. The median EBRT dose and number of fractions were 20 Gy and 5, respectively. The median total number of cycles and total dose of Lu177-PSMA received were 5 and 921.7 mCi. At a median follow-up of 1.2 months, two patients demonstrated any grade acute toxicity. One patient who completed palliative radiation to the cervical spine experienced acute grade 1 toxicity which included decreased energy and generalized weakness. The second patient experienced acute grade 3 toxicity, which was noted to be worsening of grade 3 fatigue that was present prior to initiating either EBRT or Lu177-PSMA. Of the two patients with a follow up of >90 days, neither patient was found to have chronic toxicity of any grade. Of the five patients that had clear documentation of symptom relief following dual treatment, four patients demonstrated some degree of relief, and two patients experienced complete resolution of cancer related symptoms at the irradiated site.
Conclusion: This study appreciated one case of acute grade 1 toxicity and one case of worsening pre-existing high-grade acute toxicity with the co-administration of EBRT with Lu177-PSMA. Combination therapy is likely effective for symptom palliation but longer follow-up for chronic toxicity is needed.