Metastasis-directed Therapy in Treating Nodal Oligorecurrent Prostate Cancer: A Multi-institutional Analysis Comparing the Outcome and Toxicity of Stereotactic Body Radiotherapy and Elective Nodal Radiotherapy.

BACKGROUND: Stereotactic body radiotherapy (SBRT) and elective nodal radiotherapy (ENRT) are being investigated as metastasis-directed treatments in oligorecurrent prostate cancer (PC); however, comparative data are still lacking. OBJECTIVE: To compare outcome and toxicity between both treatments. Primary endpoint was metastasis-free survival, adjusted for selected variables (aMFS). DESIGN, SETTING, AND PARTICIPANTS: This was a multi-institutional, retrospective analysis of 506 (SBRT: 309, ENRT: 197) patients with hormone-sensitive nodal oligorecurrent PC (five or fewer lymph nodes (LNs; N1/M1a), treated between 2004 and 2017. Median follow-up was 36 mo (interquartile range 23-56). INTERVENTION: SBRT was defined as a minimum of 5 Gy per fraction to each lesion with a maximum of 10 fractions. ENRT was defined as a minimum dose of 45 Gy in up to 25 fractions to the elective nodes, with or without a simultaneous boost to the suspicious node(s). The choice of radiotherapy (RT) was at the discretion of the treating physician, with treatments being unbalanced over the centers. OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS: In total, 506 patients from 15 different treatment centers were included. Primary treatment was radical prostatectomy, RT, or their combination. Nodal recurrences were detected by positron emission tomography/computer tomography (97%) or conventional imaging (3%). Descriptive statistics was used to summarize patient characteristics. RESULTS AND LIMITATIONS: ENRT was associated with fewer nodal recurrences compared with SBRT (p < 0.001). In a multivariable analysis, patients with one LN at recurrence had longer aMFS after ENRT (hazard ratio: 0.50, 95% confidence interval 0.30-0.85, p = 0.009). Late toxicity was higher after ENRT compared with that after SBRT (16% vs. 5%, p < 0.01). Limitations include higher use of hormone therapy in the ENRT cohort and nonstandardized follow-up. CONCLUSIONS: ENRT reduces the number of nodal recurrences as compared with SBRT, however at higher toxicity. Our findings hypothesize that ENRT should be preferred to SBRT in the treatment of nodal oligorecurrences. This hypothesis needs to be evaluated in a randomized trial. PATIENT SUMMARY: This study investigated the difference between stereotactic and elective nodal radiotherapy in treating limited nodal metastatic prostate cancer. Nodal relapse was less frequent following elective nodal radiotherapy than following stereotactic body radiotherapy, and thus elective nodal radiotherapy might be the preferred treatment.