Room: ePoster Forums
Purpose: Use of mixed energies is very common in 3D treatment planning and also various investigators have reported clinical advantage of use of mixed energies for IMRT treatment planning. Limitations were noted to use mixed energies for VMAT using Eclipse planning system. In this study an innovative approach was adopted to implement VMAT with mixed energies and compare plans with IMRT and VMAT with single and mixed energies using 6MV and 15MVphoton beams.
Methods: Ten prostate cancer patients treated with hypofractionated radiation to 70 Gy in 28 fractions at our institution were re-planned. Keeping optimization parameters and techniques the same, eight separate plans were generated for each patient: static IMRT 6MV (SI6), static IMRT 15 MV (SI15), static IMRT mixed energy (SIME), single arc 6 MV (SA6), single arc 15MV (SA15), double VMAT 6MV (DA6), double arc 15MV (DA15), and double arc mixed energy (DAME). To circumvent the inability of Eclipse(VMAT} plans, mixed energy plans (SIME and DAME) were created by summing a 6MV and 15MV VMAT plans. Dose-volumetric data for all plans for PTV, Rectum, Bladder and femoral heads were compared for the entire cohort using Mann-Whitney U test to evaluate variance per parameter and once identified, individual plans were tested for superiority using across the minimum, maximum and median using nonparametric testing.
Results: 8 plans were generated for each patient. Mann-Whitney testing identified significant variance for PTV and other structures. However, nonparametric testing of these clinical endpoints did not show significant statistical difference. VMAT plans could take advantage of the dosimetric characteristics of mixed energy photons to improve plan quality and outcomes.
Conclusion: Although no significant statistical difference for VMAT plans with mixed energy photons was noted in this study. However, there is clinical advantage of mixed energy VMAT plans for deep seated tumors.