Image-Based Recurrence Patterns After Reirradiation in Prostate Cancer with Long-Term Follow-Up.

Purpose: Local failure of prostate cancer after definitive radiation therapy is associated with poor prognosis. Studies on reirradiation have primarily focused on toxicity and oncologic outcome and only partially reported recurrence patterns. Investigating the recurrence pattern may help guide future therapy decisions. Methods and Materials: Thirty-three men with local recurrence of prostate cancer after primary definitive radiation therapy were enrolled between 2012 and 2018 (median age 69.8 years [IQR: 6.8], median prostate-specific antigen 4.1 ng/mL [IQR: 3.8]). Twenty-three patients received reirradiation with focal high dose-rate brachytherapy, and 10 received stereotactic body radiation therapy to the prostate with (8/10) or without (2/10) a simultaneous integrated boost to the recurrent tumor. The sites of recurrences were examined with multiparametric magnetic resonance imaging and compared with the dose distribution maps. Results: During the median 99 months (IQR: 56) follow-up, 25 patients had biochemical rerecurrence. Twenty had adequate imaging. Five patients had rerecurrences solely inside the high-dose region, and 7 had both inside and outside the high-dose region. Two patients with a prostatic recurrence received whole-gland stereotactic body radiation therapy without a boost to the tumor. Four had a combination of rerecurrence within the prostate as well as regional lymph node metastases. One patient had a prostatic rerecurrence and a single bone metastasis. One patient had prostatic rerecurrence, lymph node metastases, and bone metastases. No patients had only regional or distant metastases. Conclusions: After reirradiation of prostate cancer, the tumor frequently recurred within the prostate, both inside and outside the high-dose region. About 1 in 3 patients also had regional or distant metastatic disease at rerecurrence.