A Dosimetric Comparison of Tomotherapy and Volumetric Modulated Arc Therapy in the Treatment of High-Risk Prostate Cancer With Pelvic Nodal Radiation Therapy

Abstract

To compare the dosimetric results of volumetric modulated arc therapy (VMAT) and helical tomotherapy (HT) in the treatment of high-risk prostate cancer with pelvic nodal radiation therapy. Plans were generated for 10 consecutive patients treated for high-risk prostate cancer with prophylactic whole pelvic radiation therapy (WPRT) using VMAT and HT. After WPRT, a sequential boost was delivered to the prostate. Plan quality was assessed according to the criteria of the International Commission on Radiation Units and Measurements 83 report: the near-minimal (D98%), near-maximal (D2%), and median (D50%) doses; the homogeneity index (HI); and the Dice similarity coefficient (DSC). Beam-on time, integral dose, and several organs at risk (OAR) dosimetric indexes were also compared. For WPRT, HT was able to provide a higher D98% than VMAT (44.3 ± 0.3 Gy and 43.9 ± 0.5 Gy, respectively; P=.032) and a lower D2% than VMAT (47.3 ± 0.3 Gy and 49.1 ± 0.7 Gy, respectively; P=.005), leading to a better HI. The DSC was better for WPRT with HT (0.89 ± 0.009) than with VMAT (0.80 ± 0.02; P=.002). The dosimetric indexes for the prostate boost did not differ significantly. VMAT provided better rectum wall sparing at higher doses (V70, V75, D2%). Conversely, HT provided better bladder wall sparing (V50, V60, V70), except at lower doses (V20). The beam-on times for WPRT and prostate boost were shorter with VMAT than with HT (3.1 ± 0.1 vs 7.4 ± 0.6 min, respectively; P=.002, and 1.5 ± 0.05 vs 3.7 ± 0.3 min, respectively; P=.002). The integral dose was slightly lower for VMAT. VMAT and HT provided very similar and highly conformal plans that complied well with OAR dose-volume constraints. Although some dosimetric differences were statistically significant, they remained small. HT provided a more homogeneous dose distribution, whereas VMAT enabled a shorter delivery time.