Magnetic resonance guided stereotactic reirradiation for locally recurrent prostate cancers: Long-term results from a prospective registry study.

[BACKGROUND AND PURPOSE] Local recurrence is the most common site for prostate cancer after radical prostatectomy (RP) or radiation therapy. Treatment beyond palliative androgen deprivation therapy (ADT) are required. Stereotactic reirradiation using magnetic resonance-guided radiation therapy (MRgRT) emerged as a promising approach. This study assessed the outcomes and toxicities of 5 × 6 Gy and 6 × 6 Gy MRgRT for local-only recurrences.

[MATERIALS AND METHODS] 108 patients treated with MRgRT were included and divided into two groups: 5 × 6 Gy (67 patients) and 6 × 6 Gy (41 patients). The primary endpoint was biochemical recurrence-free survival (bRFS). Secondary endpoints included local recurrence free-survival (lRFS), metastasis-free survival (MFS), overall survival (OS) rates, and treatment toxicities. Toxicity was assessed according to CTCAE v5.0.

[RESULTS] The median follow-up was 31.9 months (range 1.5-63): 50.0 months (range 4-63) in the 5 × 6 Gy group and 17.2 months (range 1.5-34) in the 6 × 6 Gy group. The median bRFS was 18.3 months (95 % CI: 15.0 - 24.3) and 22.8 months (95 % CI: 18.3-not reached) in the 5 × 6 Gy and 6 × 6 Gy groups, respectively (p = 0.32). The median lRFS was 25.3 months (95 % CI: 18.5 - NA) in the 5 × 6 Gy group and was not reached in the 6 × 6 Gy group (p = 0.07). PSA doubling-time was statistically associated with bRFS (p = 0.04). Three cases of grade 3 late genitourinary toxicity appeared in the 5 × 6 Gy group.

[CONCLUSION] Reirradiation with MRgRT is an effective treatment for locally recurrent prostate cancer. Dose escalation showed promising outcomes with low toxicity, highlighting the need for larger prospective studies.