Mikayla Eskens, MS, Helen Nguyen, MS ∗, William Deere, MS, RT(T), Nishele Lenards, PhD, CMD, RT(R)(T), FAAMD, Ashley Hunzeker, MS, CMD, Matt Tobler, CMD, R.T.(T)
Medical Dosimetry Program at the University of Wisconsin, La Crosse, WI, USA

Applying dual, or mixed photon energies during radiation therapy is a common practice in 3-dimensional conformal radiation therapy (3D-CRT). Mixed photon energies are used to provide uniform dose coverage to a planning target volume (PTV) that ranges in depth from the skin surface. Though the application of mixed photon energies in 3D-CRT was once the convention for treating anal cancers with lymph node involvement (AC-LNI), the advantages offered by volumetric modulated arc therapy (VMAT) prove to be the optimal form of therapy for AC-LNI. Recently, multiple researchers have uncovered benefits in employing multiple photon energies in VMAT planning for prostate cancer. A retrospective study was completed to assess the impact of implementing mixed energy VMAT planning in comparison to conventional single energy VMAT planning for AC-LNI. Data from 20 patients with AC-LNI was collected to analyze the dosimetric effects of mixed energy VMAT treatments in terms of PT V conformity index, PT V homogeneity index, monitor unit usage, and organs at risk sparing. For each patient 3 treatment plans were created: a single energy 6 MV plan, a single energy 10 MV plan, and a mixed 6 MV and 10 MV energy plan. Analysis of the resulting dosimetric outcomes showed statistical significance. The current study concluded that mixed energy VMAT plans have some effect on treating AC-LNI when compared to single energy VMAT plans.