VIRTUAL HDR CYBERKNIFE® TREATMENT FOR LOCALIZED PROSTATE CANCER. PRELIMINARY EXPERIENCE

Aim: The Cyberknife is an imaging-guided device for delivering high radiation doses to a precisely defined threedimensional target volume. The Virtual HDR Cyberknife is indicated for patients with localized cancer prostate (T1-T2b) with favorable prognosis (Gleason score ≤6, PSA ≤10 ng/ml) and selected patients with intermediate prognosis (Gleason score of 7, PSA 10.2-20 ng/ml). The low α/ß ratio for prostate cancer requires high radiation with an hypofractionated schedule of dose for tumor control and it has been shown to be biologically lethal for prostate cancer cells. In this report, we summarize preliminary experience with planning emulating HDR brachytherapy dose distribution. Patients and Methods: At our institution, over a period of 36 months, 11 patients with a median age of 78 (range 73-86) years and a median Gleason score of 6 (range 5-7) were submitted to treatment with the Virtual HDR Cyberknife. The planning target volume (PTV), defined with MRI and CT imaging, included the prostate and seminal vesicles, plus 2 mm of expansion for favorable prognosis or 5 mm for intermediate prognosis in all directions, except posteriorly. The prescription dose was 38 Gy in four fractions with an extraurethral PTV Dmax at least 150% of the prescription of dose. The Fiducial Tracking System follows the fiducials that are placed one week before. Results: A dose of 38 Gy in four fractions with a median dose of 60% (range 57-75%) was prescribed for all patients. No biochemical failures were observed in a median follow-up of 12 (range 3- 36) months. The median value of pre-treatment PSA was 8.8 (range 4.5-14.3) ng/ml and this decreased in patients with a follow-up of more than three months, with a median value of 0.16 (range 0.032-1.21) ng.ml. Acute and late grade 2-3 rectal or urinary toxicities were observed in some patients. Only one patient had acute G3 rectal toxicity. One patient died of other causes. Conclusion: The Virtual HDR Cyberknife is a noninvasive and safe method for low-intermediate risk prostate cancer, improving PSA response. Further work is needed to investigate late complications and effective tumor control.