Feasibility of dose escalation in prostate cancer : a dosimetric study between IMRT, VMAT and Hybrid-arc

Abstract

Background and objectives: Prostate cancer is one of the most prevalent cancers among men in the world. Radiotherapy is one of the mainstream treatments. Intensity modulated radiation therapy (IMRT), Volumetric modulated arc therapy (VMAT) and Hybrid-Arc are the advanced treatment modalities in the radiotherapy that can deliver high dose to the planning target volumes (PTVs) while provide good sparing to the organs at risk (OARs). Dose escalation in prostate cancer is encouraged in many studies. The purpose of this study is (1) to assess the feasibility of dose escalation by boosting the dose to whole prostate to 84Gy using IMRT, VMAT and Hybrid-Arc under Queen Elizabeth Hospital protocol (2) to compare the dosimetric outcomes between 9-field IMRT, 2-arc VMAT and Hybrid-Arc (3-field conformal plus 1 full VMAT arc) in these dose escalated plans. Methods and Materials: The planning computed tomography images of 16 patients who received radiotherapy treatment for prostate cancer before were recruited. Each case will have 3 plans using IMRT, VMAT and Hybrid-Arc planning. Dose escalation was attempted with 84Gy to whole prostate as clinical target volume (CTV1), and 78Gy and 72Gy prescribed to, PTV1 and PTV2 respectively. All plans have to meet the constraint of the OARs and the dose coverage of PTVs were assessed for the feasibility. Target volumes parameters and OAR parameters between IMRT, VMAT and Hybrid-Arc were compared. Results: D95% of CTV1, PTV1 and PTV2 could be boosted up to 81Gy, 75Gy and 68Gy respectively. The homogeneity index of PTV1 in VMAT was statistically significantly better than IMRT plans (VMAT: 0.186; IMRT: 0.210). V30Gy of rectum in Hybrid-Arc plans were statistically significantly lower than IMRT and VMAT plans (Hybrid-Arc: 57%; IMRT: 68%; VMAT: 64%) while IMRT plans showed the lowest V70Gy of rectum (IMRT: 5%; VMAT: 8%; Hybrid-Arc: 8%). VMAT plans showed the lowest value of both V30Gy and V40Gy in bilateral femoral heads. The monitor units required for VMAT and Hybrid-Arc plans were also statistically significantly fewer than IMRT plans. Conclusions: Dose escalation of prostate plans to the target doses under current study protocol was not feasible. VMAT was suggested to perform better than IMRT and Hybrid-Arc in these plans.