Encrypted login | home

Program Information

Impact of Daily Image Guidance to Prostate Fiducial Markers On Pelvic Lymph Node (PLN) Irradiation for Prostate Patients Receiving SBRT

no image available
M Cloutier

M Cloutier*, E Hipp , X Tang , C Tomer , J Mechalakos , M Hunt , M Zelefsky , N Tyagi , Memorial Sloan-Kettering Cancer Center, New York, NY


SU-H1-GePD-J(B)-3 (Sunday, July 30, 2017) 3:00 PM - 3:30 PM Room: Joint Imaging-Therapy ePoster Lounge - B

Purpose: To determine the impact of using fiducial marker s to match for daily image guidance on the PLN for prostate cancer patients treated with SBRT

Methods: 36 patients underwent SBRT treatment to prostate and PLN from 2014-2016. Each patient received either 800cGyx5 or 500cGyx5 to the prostate and 500cGyx5 to PLN. A 5 mm margin around the PLN was used for planning. Two registrations for each of the daily cone beam CTs were performed: a rigid registration to fiducials and a rigid registration to the pelvic bones (surrogates of PLN match). Bladder and rectum variation during treatment was evaluated by contouring the rectum and bladder volume within the CBCT scans volume. Average translation difference between fiducial and bony match as well as percentage fractions with shifts greater than 5 mm were calculated for the entire population. Changes in bladder and rectum volume with respect simulation volume and their impact on translational shifts were also evaluated.

Results: A total of 12 patients (60 CBCTs) have been analyzed to date. The average translational difference between fiducial match and bony match was -0.1±0.9, 1.7±3.9, -1.9±4.2 and 5±3.8 mm for lateral, vertical, longitudinal and vector shifts, respectively. percentage fractions with shifts greater than 5 mm are 0, 25, 5, and 33 percent for lateral, vertical, longitudinal and vector shifts. Average change in bladder and rectum volume from simulation volume and was -36.8±138.7 cc and -0.7±26 cc.

Conclusion: Our preliminary analysis suggests that the current 5 mm margin is sufficient for majority of prostate patients getting PLN irradiation with SBRT. Patients with larger shift were due to larger variation in bladder volume as compared to variation in rectum volume. A consistent bladder and/or rectum filling compared to pre-simulation volume is essential for adequate coverage of PLN in hypofractionation setting.

Contact Email: