Author: Aliasghar Rohani, Rui Zhang 👨🔬
Affiliation: Louisiana State University, Baton Rouge, Louisiana, Department of Radiation Oncology, Mary Bird Perkins Cancer Center 🌍
Purpose: This study aimed to evaluate the impact of simultaneous optimization of multi-photon beam energy and fluence on IMRT and VMAT treatment planning.
Methods: An Elekta linear accelerator (linac) model was created using Monte Carlo simulations (BEAM/EGS nrc) for 6 MV beam, and after validation, the model was used to generate 2 and 4 MV beams. We developed an in-house framework to optimize the fluence and beam energies (2-18 MV) simultaneously, and evaluated the combinations of two, three and four photon beam energies for both IMRT and VMAT planning. The methodology was applied to a prostate cancer patient, comparing standard 6 MV VMAT plans with multi-energy IMRT (ME-IMRT) and VMAT (ME-VMAT) plans. Dosimetric assessments were performed for planning target volume (PTV) and organs-at-risk (OARs).
Results: We evaluated 23 different energy combinations. Incorporating higher energies like 10 MV and 18 MV into the optimization process reduced entrance dose, benefiting cases requiring skin sparing while maintaining comparable dose coverage to 6 MV plans. Multi-energy optimization with three or four energies didn’t significantly improve dose statics. Plans combining 4 MV and 10 MV achieved similar mean doses as 6 MV plan while reducing the maximum bowel dose by 11.3 %. Compared to the 6 MV VMAT plan, the combination of 6 and 18 MV in the VMAT plan resulted in a 7.5% reduction in D50 and a 14.8% reduction in the maximum dose to normal tissues outside the PTV.
Conclusion: While multi-energy optimization with more than three energies showed limited dosimetric improvement, selective two-energy combinations could improve normal tissue sparing without compromising target coverage. Further investigation is needed to identify clinical scenarios where multi-energy approaches may have a greater impact.