3460 - Stereotactic Body Radiation Therapy (SBRT) to Sites of Oligoprogression during Lutetium-177-PSMA-617 (Lu-PSMA) Treatment for Metastatic Castrate Resistant Prostate Cancer

02:30pm - 03:45pm PT

Hall F

Screen: 28

POSTER

Presenter(s)

Adam Kessel, MD - Mayo Clinic Rochester, Rochester, MN

A. C. Kessel¹, M. Muniz², T. J. O'Byrne³, R. Phillips¹, S. S. Park¹, B. J. Davis¹, B. J. Stish¹, C. R. Choo¹, K. W. Merrell¹, E. D. Kwon⁴, G. B. Johnson⁵, F. J. Quevedo², J. Orme², D. Childs², and J. M. Wilson¹; ¹Department of Radiation Oncology, Mayo Clinic, Rochester, MN, ²Department of Medical Oncology, Mayo Clinic, Rochester, MN, ³Department of Quantitative Health Sciences, Mayo Clinic, Rochester, MN, ⁴Department of Urology, Mayo Clinic, Rochester, MN, ⁵Mayo Clinic, Division of Nuclear Medicine, Rochester, MN

Purpose/Objective(s): The use of SBRT to address sites of resistant disease in men receiving Lu-PSMA for metastatic prostate cancer has been implemented in only limited situations. Patients may be treated with SBRT for up to 5 sites of oligoprogression or non-responding lesions, as determined by therapy monitoring SPECT/CT and followed by interim restaging PSMA PET/CT after 3 or 6 cycles. We have previously described the safety of this approach and now report on the efficacy of SBRT to resistant metastases among patients receiving Lu-PSMA.

Materials/Methods: This retrospective single institution study analyzed patients with metastatic prostate cancer treated with Lu-PSMA, who had 1-5 sites of oligoprogression or persistent disease treated with SBRT. Radiographic progression-free survival (rPFS) was defined as the time from SBRT initiation to radiologic progression per PSMA or Choline PET, while overall PFS included PSA and/or radiographic recurrence. Most patients (n = 29) on this study received PET (PSMA or Choline) every 3-6 months.

Results: 51 lesions in 31 patients were treated with SBRT (median 1 lesion per patient; range 1-4). All patients had previously progressed on prior taxane based chemotherapy and androgen receptor pathway inhibitor, 16% of patients had progressed on second-line chemotherapy as well. Most (84%) patients completed all 6 cycles of Lu-PSMA (range 4-6). SBRT was delivered after cycle 3 or 4 in 42% and after cycle 6 in 32%. SBRT was delivered in 1-5 fractions, most common being 20 Gy in 1 fraction (67%) followed by 30 Gy in 3 fractions (21%). At median follow-up of 1.2 years, local control rate at 6 months was 96.8%. The median rPFS and PFS were 3.6 months (2.4, 4.8), and 19.4% of patients (n=6) remained free of progression at 6 months. Overall survival at 6 and 12 months was 90.3% and 80.4%, with a median overall survival of 1.1 years (0.6-1.5). At time of progression, 60% had oligo-progression in 5 or less lesions.

Conclusion: SBRT to non-responding disease during Lu-PSMA provides excellent local control, and nearly 20% achieved durable disease control. Most patients had potentially salvageable disease with local therapies. Additionally, patients had excellent OS for this population that would be expected to have worse outcomes given early progression. These results support the concept that the selective addition of SBRT to sites refractory to Lu-PSMA therapy is a viable option for heavily-treated populations with limited alternative therapy.