Simultaneous Integrated Boost Plan Comparison between Volumetric Modulated Arc Therapy (VMAT) and Intensity Modulated Radiation Therapy (IMRT) for Prostate, Seminal vesicle and Lymph Node Irradiation

Objectives: We performed a planning study to evaluate the dosimetric differences between Volumetric Modulated Arc Therapy (VMAT) and Intensity Modulated Radiation Therapy (IMRT) using simultaneous Integrated Boost (SIB) for prostate cancer cases. Methods: 20 prostate cancer patients scheduled for SIB-VMAT treatment on the Halcyon TM 2.0 linear accelerator were recruited for this study and SIB-IMRT plans were generated for comparison purpose. The pelvic lymph nodes (PTV46), the seminal vesicle (PTV50), and the prostate (PTV60) were simultaneously treated to 46 Gy 50 Gy, and 60 Gy delivered in 20 fractions respectively. Results: SIB-VMAT was better due to its higher (1.41%) CI, lower (2.7%) HI, and lower (26%) GI than SIB-IMRT for PTV60. For PTV50, a higher (7.3%) CI, lower (48%) HI, and a lower (31.73%) GI for SIB-VMAT compared to SIB-IMRT. Also, for PTV46, a higher (9.4%) CI, lower (2.5%) HI, and a lower (16.4%) GI were achieved by SIB-VMAT compared to SIB-IMRT. Conclusion: Better conformal and slightly similar homogeneous dose distribution were noticed in SIB-VMAT plans compared to SIB-IMRT plans. However, SIB-IMRT provided better OARs sparing of the bladder and the femoral heads while SIB-VMAT had better sparing for rectum.