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Patients with local recurrence after prostatectomy and post-operative radiotherapy are a real challenge  for salvage treatment. The local treatment options are limited and literature on that issue is scarce. This study aims to evaluate the value of stereotactic body radiation therapy (SBRT) in the treatment of local recurrence, in patients who had already undergone salvage or adjuvant post-prostatectomy radiotherapy to the prostate bed.

The study group consists of 23 patients with locally recurrent prostate cancer after prostatectomy and salvage (20; 87%) or adjuvant (3; 13%) radiotherapy, treated with salvage SBRT between 2014 and 2020, at a mean age of 69 years (51-80). The mean pre-SBRT PSA level was 4.62 ng/ml (0.008-39 ng/ml), 14 patients (61%) had ISUP Grade Group (GG) of ≤3, and 9 patients (39%) had GG ≥4. The average time between salvage/adjuvant RT and local recurrence was 5 years. The recurrence was retrovesical in 12 (52%), periurethral in 9 (39%), and both regions were involved in two (9%) patients. In 14 patients (61%) local recurrence was the only site of failure, whereas in 9 patients (39%) it was accompanied by oligometastatic regional (8; 35%) or distant lesions (1; 4%), which were also treated with SBRT. All patients were treated with focal SBRT to the local failure with dose per fraction ranging from 5 Gy to 12 Gy and the total dose ranging from 24 Gy to 36.25 Gy. The most common (12; 52%) SBRT schedule was 33.75- 36.25 Gy in 5 fractions. 11 patients (48%) were treated with CyberKnife, and 12 (52%) with linear accelerator. Fifteen patients (65%) continued or were given ADT together with SBRT. The treatment outcome was evaluated for biochemical response (BR) defined as the decrease of PSA below the pre-SBRT level, biochemical control (BC) defined as PSA value below 0.2 ng/ml, and overall survival (OS). All that end-points were calculated with an actuarial method. The chance of biochemical control was also assessed in relation to selected clinical factors.

Median follow-up was 28 months. One- and 2-years OS were 95% and 85%, 1- and 2-years BR were 84% and 66%, and 1- and 2-year BC were 50% and 50%, respectively. The biochemical recurrence was observed in 50% and 75% of patients with GG of ≤3 and ≥4, respectively. Patients who experienced biochemical recurrence after SBRT had a mean pre-SBRT PSA value of 6.9 ng/ml as compared to 2.34 ng/ml in those with BC. The time between primary RT and local failure was 59 and 69 months, respectively. Despite numerical differences between some comparisons, none of the analyzed factors were statistically significant.

SBRT for locally recurrent prostate cancer after prostatectomy and radiotherapy may lead to the biochemical response in a majority of patients. However, the durable biochemical control is somewhat limited. Proper selection of patients can be of pivotal importance.