Purpose

To evaluate oncologic outcomes and treatment-related toxicity in patients with prostate cancer treated with permanent seed implant brachytherapy, either as monotherapy or combined with external beam radiation therapy (EBRT) and/or androgen deprivation therapy (ADT).

Material and methods

Between 2008 and 2023, a retrospective cohort of 805 patients with prostate cancer underwent permanent iodine-125 seed implant brachytherapy. Of these, 394 (48.9%) were classified as low risk, 303 (37.6%) as intermediate risk, and 108 (13.4%) as high risk, according to the D’Amico classification. Low-risk patients were treated with brachytherapy alone, whereas intermediate- and high-risk patients received combined brachytherapy with EBRT (50 Gy). ADT was administered for 6 months in intermediate-risk patients and for 18-36 months in high-risk patients, according to institutional practice. The prescribed brachytherapy dose was 145 Gy for monotherapy and 110 Gy for brachytherapy combined with EBRT. Biochemical recurrence was defined according to the Phoenix criteria.

Results

Biochemical relapse-free survival (bRFS) remained high across risk groups, with disease control rates of 95.3% in low-risk, 96.0% in intermediate-risk, and 94.3% in high-risk patients. Eight patients with local recurrence after prior radiotherapy underwent salvage brachytherapy; seven remained disease-free at last follow-up. Late grade ≥ 2 genitourinary or gastrointestinal toxicity occurred in 0.9% of patients treated with brachytherapy alone and in 4.0% of those receiving combined therapy. No grade 4 or 5 toxicities were observed.

Conclusions

Permanent seed brachytherapy provides durable oncologic control with a low incidence of clinically significant toxicity across different risk groups. In the salvage setting, outcomes should be interpreted cautiously due to small number of patients. These findings support the role of permanent seed brachytherapy as an effective and well-tolerated treatment option for appropriately selected patients.