Does helical tomotherapy improve dose conformity and normal tissue sparing compared to conventional IMRT? A dosimetric comparison in high risk prostate cancer.

The study was designed to compare Helical Tomotherapy (HT) based IMRT and conventional sliding window (SW IMRT) in patients with high risk prostate cancer. Complementary plans with HT and SWIMRT were compared using DVH parameters. The PTV Prostate was prescribed 74 Gy in 37 fractions and the nodal PTV received 55 Gy in 37 fractions by simultaneous integrated boost. Conformity Index, Homogeneity Index and dose-volume parameters were compared. The conformity index (CI) of HT (0.77, SD = 0.54) plans tended to be better (p = 0.069) compared to SWIMRT (0.70, SD = 0.01) for prostate PTV. CI for nodal PTV was similar. Helical tomotherapy plans were more homogeneous, with homogeneity index (HI) of 0.04 compared to 0.06 in SWIMRT (p = 0.018) for PTV prostate and HI of 0.06 and 0.15 (p = 0.025) for PTV nodes respectively. Median dose to bladder (p = 0.025) and rectum (p = 0.012) were less with HT. However, HT delivered a higher D10Gy and D1Gy to rectum and bladder overlap volumes as a consequence of achieving better homogeneity. Femoral heads were better spared with HT plans (p = 0.012). HT improves dose homogeneity, target coverage and conformity as compared to SWIMRT, with overall improvement in critical organ sparing.