Stereotactic body re-irradiation therapy for locally recurrent prostate cancer after external-beam radiation therapy: Initial report.

Purpose: Management of prostate cancer relapses after external-beam radiation therapy is still undefined. Re-irradiation schedules have been explored in different tumour sites. In this report, we present our preliminary experience of re-irradiation using stereotactic body radiotherapy for localized prostate cancer failure.

Material And Methods: Between March 2011 and October 2014, robotic stereotactic body radiation therapy was administered to patients previously treated with external-beam radiation therapy to a median dose of 71.1Gy (range, 45-76.5Gy) and with biochemical failure corresponding to a local in-field recurrence of prostate cancer. Ten patients had recurrences after postoperative external-beam radiotherapy. Patients underwent a pelvic MRI to confirm the recurrence and a total body staging using a ((18)F)-fluorocholine PET/CT. The prescription dose consisted of five fractions of 7.25Gy to a total dose of 36.25Gy. Efficacy was evaluated based on biochemical response and toxicity was evaluated according to CTCAE v.4.0 questionnaires and International Prostate Symptom Score.

Results: Twenty-one patients were treated and followed for a median time of 11.7 months (mean: 13.4 months; range: 2.5-46.5 months). Median time between the first external-beam radiation therapy of prostate cancer and the first day of CyberKnife(®) treatment was 111 months (range: 38-398 months). One-year biochemical recurrence-free survival rate was 83.3%, and only one in-field progression was reported. Two patients had a biochemical failure corresponding to metastatic progression without evidence of local recurrence. Treatment was well tolerated, with only one grade 2 acute genitourinary toxicity, no grade≥2 acute gastrointestinal or late toxicities were reported.

Conclusion: Stereotactic body re-irradiation therapy using CyberKnife(®) after failed external-beam radiation therapy showed favourable results in terms of in-field local and biochemical control. Toxicity was low and acceptable. Further prospective studies are needed to confirm these results to select patient and to evaluate the introduction of androgen-deprivation therapy.