Sci-Sat AM(2): Brachy-02: Image guided brachytherapy (IGBT) for HDR prostate treatment : Pre-treatment verification...

Prostate HDR brachytherapy utilizes flexible catheters for treatment delivery. Catheters are inserted under US guidance and planning performed on CT images. This study investigates the efficacy of performing kV cone beam imaging prior to treatment to quantify catheter displacement and dose delivered.

Twenty consecutive patients undergoing HDR prostate brachytherapy were planned using CT images. Under US guidance, catheters and four fiducial markers were placed into the prostate. Before treatment, visual check confirmed no movement of the template sutured to the perineum and no movement relative to the template. Cone beam imaging was performed using an isocentric mobile c-arm. Catheters were re-adjusted if required by the Radiation Oncologist. The cone beam images prior to adjustment were later fused with the planning CT.

In 17 of the 20 patients, catheter displacements exceeding 0.5cm were observed. Compared to the CT based plan, an average catheter displacement of 1.0cm results in a decrease in the V100 of the prostate by approximately 27%, urethra V120 increased by about 7%, and urethra D10 increased by about 4%. Approximately 65% of patients had average catheter displacements of 1.0cm and larger. Three patients had catheter shifts larger than 2cm.

Catheter movement within the patient can be significant and cone beam imaging prior to treatment delivery provides precise imaging to determine catheter displacement. Cone beam imaging time using an isocentric C-arm is sufficiently short enough (∼ 2 minutes) so as to make this a viable quality assurance tool in the OR.