Prostate Delineation for LDR Prostate Brachytherapy: Concordance Study Between Clinical Specialist Radiation Therapist and Radiation Oncologist

Abstract

Permanent seed brachytherapy for prostate cancer is a transperineal technique where radioactive sources are either permanently implanted into the prostate. Recently, funding guidelines for permanent seed implants as a treatment option for men with prostate cancer have changed in Ontario with funding now available for men with low and intermediate risk disease. As a result, the number of permanent seed prostate brachytherapy treatments has increased. Given radiation oncologist (RO) time constraints, we propose exploring the delegation of target delineation of the prostate for permanent seed treatment planning to an advanced practice clinical specialist radiation therapist (CSRT) in brachytherapy. The primary aim of this study is to determine the feasibility of CTV target delineation by the brachytherapy CSRT by testing the concordance between CSRT delineation and the gold standard. Between February 2013 and May 2013, 23 TRUS volume studies were completed on prostate cancer patients considering LDR permanent seed brachytherapy treatment. Acquired ultrasound images were imported into VariSeed treatment planning system (Varian Medical System Inc. Palo Alto, CA) for contouring. Prostate contours were completed independently by one CSRT and one Radiation Oncologist (RO, gold standard). All contours were then exported to MiMVISTA (MIM software Inc. Cleveland, OH) for analysis. Total prostate volume, union and intersection volumes were determined. To assess similarity of prostate volumes between the CSRT and the RO, the DICE index was used. The index is a scale from zero to one with an index of zero indicating no overlap of contours and an index of one representing complete unity or overlap of contours. The mean prostate volume for all 23 patients was 34.75cc vs. 37.33cc between the CSRT and the gold standard respectively. The mean DICE index value was 0.92 (range 0.82-0.95). The areas of greatest variability occurred at the base and apex of the prostate. This feasibility study found that there is high concordance between prostate delineation performed by an advanced practice CSRT and an RO. These early findings provide evidence that CSRTs are capable of accurately contouring prostate volumes on TRUS volume studies. Future work will describe the variability between all ROs performing prostate brachytherapy and the CSRT.