Dosimetric verification of the dose calculation algorithms in real time prostate brachytherapy

BACKGROUND: During real time prostate brachytherapy different calculation algorithms can be used which gives the opportunity to modulate the dwell times and positions of the source and consequently the dose distribution and values of therapeutic indices [1]. AIM: The aim of this study was the dosimetric verification (in-phantom) of three optimization algorithms for dose calculation during real-time prostate brachytherapy. MATERIALS/METHODS: Three optimization algorithm were evaluated: geometric optimization (GO), inverse optimization (IO) and blind inverse optimization (BIO). Then treatment plans for the tissue-equivalent phantom were prepared. For each plan the same CTV, organs at risk (OARs: urethra, rectum), number of needles and geometry of implant were used. RESULTS: Measured mean doses and their standard deviations for GO, IO and BIO were respectively: 11.13 Gy and 0.01 Gy, 15.71 Gy and 0.01 Gy, 14.74 Gy and 0.02 Gy for the urethra and 10.11 Gy and 0.01 Gy, 8.97 Gy and 0.01 Gy, 8.70 Gy and 0.01 Gy for the rectum. Comparison between doses measured by semiconductor detectors and calculated doses revealed differences in the range from 0.10 Gy between doses compared in the urethra for IO and BIO even to 2.46 Gy for GO for the same analyzed organ. For the rectum these differences were between 0.32 and 0.66 Gy. CONCLUSIONS: Qualitative comparative analysis performed for a phantom study for 3D-CBRT prostate treatment proved the correctness of verified optimization algorithms implemented in Oncentra Prostate vs. 3.0.9.