SU‐C‐16A‐01: in Vivo Source Position Verification in High Dose Rate (HDR) Prostate Brachytherapy Using a Flat Panel Imager: Initial Clinical Experience

Purpose:We report our initial clinical experience with a novel position‐sensitive source‐tracking system based on a flat panel imager. The system has been trialled with 4 prostate HDR brachytherapy patients (8 treatment fractions) in this initial study.Methods:The flat panel imaging system was mounted under a customised carbon fibre couch top assembly (Figure 1). Three gold fiducial markers were implanted into the prostate of each patient at the time of catheter placement. X‐ray dwell position markers were inserted into three catheters and a radiograph acquired to locate the implant relative to the imaging device. During treatment, as the HDR source dwells were delivered, images were acquired and processed to determine the position of the source in the patient. Source positions measured by the imaging device were compared to the treatment plan for verification of treatment delivery.Results:Measured dwell positions provided verification of relative dwell spacing within and between catheters, in the coronal plane. Measurements were typically within 2.0mm (0.2mm – 3.3mm, s.d. 0.8mm) of the planned positions over 60 dwells (Figure 2). Discrimination between larger dwell intervals and catheter differentiation were clear. This confirms important delivery attributes such as correct transfer tube connection, source step size, relative catheter positions and therefore overall correct plan selection and delivery. The fiducial markers, visible on the radiograph, provided verification of treatment delivery to the correct anatomical location. The absolute position of the dwells was determined by comparing the measured dwell positions with the x‐ray markers from the radiograph, validating the programmed treatment indexer length. The total impact on procedure time was less than 5 minutes.Conclusion:The novel, noninvasive HDR brachytherapy treatment verification system was used clinically with minor impact on workflow. The system allows verification of correct treatment delivery, free of most potential human related errors identified in ICRP 97.This research is supported by funding from the Australian Government Department of Health through Cancer Australia grant no. 616614.