SU-FF-T-35: Is High-Dose Rate (HDR) “better Than” and Low-Dose Rate (LDR) Prostate Brachytherapy? A Dosimetric Study Using Retrospective Data

Purpose: To compare high‐dose rate (HDR) and low‐dose rate (LDR permanent seeds) prostate brachytherapy using dosimetric parameters. Method and Materials: From January 2003 to August 2004, 102 HDR prostate implants were planned on the Nucletron PLATO Brachytherapy with subsequent treatment using Nucletron afterloader (I192 stepping source). During this time period, 72 LDR implants were pre‐planned on Varian Variseed Brachytherapy with subsequent treatment using I125 seeds (a combination of loose and stranded seeds). The HDR implants were forward planned using a combination of manual dwell time adjustments and graphical optimization on patient CTimages. The LDR implants were pre‐planned based on ultrasoundimages and post‐implant dosimetry was assessed at one month from CT. For this study, post‐plans were analyzed using Nucletron PLATO Brachytherapy Seeds. Parameters used for comparison included: Conformal index (COIN), Homogeneity Index (HI), Natural Dose Ratio (NDR) as well as volume and dose coverage indices. Maximum dose contribution to critical structures was reported. Results: Our results show the V100 for HDR with a mean of 96.1% is higher than LDR (post‐plan) with a mean of 81.8% (p<0.001). Conformal Index for HDR was 0.701 compared to LDR pre‐plan (COIN=0.627, p<0.001) and post‐plan (0.534, p<0.001). The homogeneity index showed a significant difference between techniques (HDR HI=0.628, LDR pre‐plan HI=0.518, HI post‐plan HI=0.425). The Natural Dose Ratio did not show a large difference (HDR NDR=1.025, LDR pre‐plan NDR=1.041, LDR post‐plan NDR=0.915). Conclusion: It has been shown high‐dose rate brachytherapy for prostate treatment delivers a more conformal and uniform dose throughout the target than low‐dose rate permanent seeds. The dose contribution to the rectum and urethra is much less with high‐dose rate than low‐dose rate. Dose contribution to the target can be tailored using existing optimization routines and newer algorithms for inverse planning that will make the planning procedure simpler.