Prostate HDR brachytherapy catheter displacement between planning and treatment delivery.

Abstract

HDR brachytherapy is used as a conformal boost for treating prostate cancer. Given the large doses delivered, it is critical that the volume treated matches that planned. Our outpatient protocol comprises two 9 Gy fractions, two weeks apart. We prospectively assessed catheter displacement between CT planning and treatment delivery. Three fiducial markers and the catheters were implanted under transrectal ultrasound guidance. Metal marker wires were inserted into 4 reference catheters before CT; marker positions relative to each other and to the marker wires were measured from the CT scout. Measurements were repeated immediately prior to treatment delivery using pelvic X-ray with marker wires in the same reference catheters. Measurements from CT scout and film were compared. For displacements of 5mm or more, indexer positions were adjusted prior to treatment delivery. Results are based on 48 implants, in 25 patients. Median time from planning CT to treatment delivery was 254 min (range 81-367 min). Median catheter displacement was 7.5mm (range -2.9-23.9 mm), 67% of implants had displacement of 5mm or greater. Displacements were predominantly caudal. Catheter displacement can occur in the 1-3h between the planning CT scan and treatment. It is recommended that departments performing HDR prostate brachytherapy verify catheter positions immediately prior to treatment delivery.