ABSTRACT
Purpose: Herein is reported our initial experience of the CyberKnife to show its safety and feasibility as a treatment modality for non-metastatic prostate cancer. Materials and Methods: Twenty patients, with biopsy-proven prostate cancers, were recruited into a phase I clinical trial using the CyberKnife. The distribution of clinical risks, as assessed using the ASTRO criteria, was as follows: low (4), intermediate (5) and high (11). The mean age and follow up of the patients were 71.4 years and 15 months, respectively. The patients received 7.5-9Gy of radiation in a single fraction for 4-5 days. The total radiation dose to the prostate was 34-37.5Gy, which approximates to 86.4Gy in 2Gy fractions. The rectal and bladder acute toxicities were graded using the criteria of the Radiation Therapy Oncology Group (RTOG). The results of acute toxicities were compared to those of the historical control, which had been treated with conventional four field box techniques (received median dose 70.2Gy). The prostate-specific antigen (PSA)- based short-term efficacy was described. Results: The acute rectal toxicity scores were 0, 1 and 2 in 13, 5, and 2 patients, respectively. The acute bladder toxicity scores were 0, 1 and 2 in 16, 3 and 1 patient, respectively. No grade 3 or 4 acute toxicity was noted. These figures contrast sharply with those found for the historical control. All toxicities spontaneously subsided within 3 months after treatment. Continuous PSA reduction was noted in all patients, and no PSA failure was noted during the follow up period. Conclusions: Our data show the feasibility of the CyberKnife in terms of its efficacy and acute toxicity. Moreover, the capability of using a hypo-fractionation schedule lead to marked improvement in patient convenience, with substantial resource savings.