Poster - Thurs Eve-15: Comparison of Cobalt-60 and 6 MV linac based tomotherapy: A prostate case study

Previous work reported by us has shown the potential for Cobalt-60 (Co-60) tomotherapy for sites with small separations such as in head and neck site. In this work we extend our investigations by comparing tomotherapy plans for the treatment of a typical prostate cancer obtained for 6 MV and Co-60 beams. Beam collimation was provided by the MIMiC® (NOMOS Corporation, Sewickly, PA) multi-leaf collimator (MLC). Both plans used 21 beam angles, each utilizing the central 10 leaf-pairs of the MLC for intensity modulation. An in-house inverse treatment planning program, based on the active-set conjugate gradient method, was used for dose-volume optimization. BEAMnrc and DOSXYZnrc Monte Carlo simulated beam and dose data, including inhomogeneity corrections, were used to calculate the optimized tomotherapy dose distributions. Prostate, rectum, and external body contours were outlined and dose-volume optimization objectives were set to deliver a minimum of 95% and a maximum of 105% of the 76 Gy dose prescription to the prostate and limiting only 20% of the rectum volume to receive ⩾ 70 Gy. A quantitative analysis of the dose distributions and dose-area histograms show that both Co-60 and 6 MV plans achieve the initial objectives for target (prostate) and organ at risk (rectum). Although the dose to the body and rectum for Co-60 is slightly higher than that for 6 MV, it satisfies the plan objectives based on the clinical dose tolerance. Our results demonstrate that Co-60 based tomotherapy can provide clinically competitive dose distributions for the treatment of prostate cancer.