Salvage image guided radiation therapy to the prostate after cryotherapy failure

Cryotherapy is an option for the primary treatment of localized prostate cancer, along with radical prostatectomy, external beam radiation therapy, and brachytherapy. Although it is known that local recurrence can occur in >20% of patients treated with primary cryotherapy, unfortunately there is a paucity of data on later salvage treatments. The use of external beam radiation therapy is an attractive option after cryotherapy failure, but there is little data on its efficacy and toxicity. We evaluated the biochemical control and complication rates of salvage dose-escalated image guided intensity modulated radiation therapy (IG-IMRT) after cryotherapy failure.

Patients who were treated at our institution from 2005 to 2016 were reviewed for those who underwent cryotherapy as initial treatment followed by salvage IGRT. Patients were treated with dose-escalated IG-IMRT using standard treatment margins of 3 mm posterior and 7 mm in all other directions and daily cone beam computed tomography or kv imaging to implanted fiducial markers. Biochemical progression was defined in accordance with the Phoenix consensus conference definition.

Eight patients were identified as having received post-cryotherapy salvage radiation within the study period. The median total dose was 77.7 Gy (range, 75.6-81.0 Gy). Median follow-up was 55 months (range, 6-88 months). Six patients remained biochemically controlled at the latest follow-up. One patient developed distant metastases after 22 months and one experienced biochemical failure at 30 months with no evidence of distant metastases. No patients experienced acute gastrointestinal toxicities of grade 2 or higher. There were no cases of late gastrointestinal or genitourinary toxicity.

High-dose IG-IMRT results in high rates of salvage and extremely low rates of serious late toxicity for patients with locally recurrent prostate cancer after cryotherapy. Although the results are encouraging, given the small number of patients in this and other series, we remain cautious with regard to this treatment and believe the use of salvage radiation therapy after cryotherapy warrants further study.