SU-FF-T-258: Hypofractionated Stereotactic Radiotherapy for Prostate Cancer Using the CyberKnife

Abstract

Purpose: To describe the investigational design, treatment planning,treatment delivery, and initial clinical results of a study on hypofractionated image‐guided prostate cancertreatment using the CyberKnife. Design characteristics of the CyberKnife that enable real‐time, 6‐D fiducial tracking with sub‐millimetric accuracy will be discussed. Treatment planning techniques, technical aspects of treatment delivery, and clinical outcome data will be presented. Method and Materials: Greater than 50 prostate cancer patients have been accrued. Patients were treated in five fractions of 7Gy each, for a total of 35 Gy over 5 to 7 days. Four fiducials were implanted using a transperineal approach. Technical details of each treatment were recorded along with treatment planning quality indicators. Follow‐up clinical data were collected including PSA kinetics and rectal and urinary complications. Results: Data will be presented from MDACC Dosimetry Service that independently confirm the dosimetric accuracy and spatial precision of the CyberKnife system used in this study. Results will be presented summarizing the mean and range of technical and physical parameters used for this study: number of beams, number of nodes, number and size of collimators,treatment time, DVH indices, along with dose conformality and homogeneity indices. Typical intra‐fraction drifts in prostate position detected by the real‐time tracking system will be discussed. At the time of abstract submission, follow‐up time for some patients exceeds twelve months. PSA and short‐term morbidity data will be presented. Conclusion: This paper reports on the first clinical study of image‐guidedrobotic x‐ray therapy for the hypofractionated treatment of prostate cancer. The study has shown that accurate, spatially precise hypofractionated treatment can be delivered in a reasonable time using the CyberKnife. The study has shown that the short‐term morbidity associated with this hypofractionated treatment regimen is very low. However, conclusions regarding long‐term morbidity and biochemical disease‐free survival will require significantly longer follow‐up.