Current role of image-guided robotic radiosurgery (Cyberknife®) for prostate cancer treatment

Objectives To describe the most recent data from phase I and II clinical trials of stereotactic body radiation therapy (SBRT) using image-guided robotic radiosurgery, specifically the Cyberknife (R) (Accuracy Incorporated, Sunnyvale, CA, USA). To better determine thecurrent role of this type of radiosurgery in prostate cancer (PCa) management. Materials and Methods Current clinical trials and relevant retrospective studies were identified from the literature, clinical trial databases, websites and conference abstracts. The indications, technical aspects, efficacy and toxicity of SBRT using the Cyberknife (R) system were summarized. Results The Cyberknife (R) system is an experimental treatment mostly used for localized PCa in stage cT1/T2a-b N0 M0 with a Gleason score <= 7 and PSA level <= 20 ng/mL. Hypofractionated radiation therapy was delivered in five fractions of 7-7.25 Gy for a total dose of 35-36.25 Gy. After treatment, the median PSA levelfell from 4.9-8.3 ng/mL to 0.1-1.6 ng/mL at a median follow-up of 4-60 months. The biochemical progression-free survival rates ranged from 78.3 to 100%. Acute and late toxicities were mostly grade 1/2 rectal or urinary complications. Few grade 3 and no grade 4 toxicities occurred during follow-up; however, erectile dysfunction and testes toxicity were also reported. Conclusions The use of the Cyberknife (R) system is limited mainly by its pretreatment and maintenance costs. Despite encouraging preliminary results, longer-term follow-up and randomized controlled phase III clinical trials are necessary before the Cyberknife (R) system becomes a standard treatment method.