Most modern LINAC are installed with a variety of photon energies varying from 6 MV to 18 MV. The conventional wisdom in external radiotherapy has been that higher energies (>10 MV) are preferred for deep seated pelvic and/or abdominal lesions, especially for larger target volume or larger patients. 1. Laughlin JS Mohan R Kutcher GJ. Choice of optimum megavoltage for accelerators for photon beam treatment.

Int J Radiat Oncol Biol Phys. 1986; 12: 1551-1557

The usefulness for higher energy is more evident with 3DCRT, as compared to IMRT and VMAT. 2. Soderstrom S Eklof A Brahme A. Aspects on the optimal photon beam energy for radiation therapy.

Acta Oncol. 1999; 38: 179-187

The recent paper by Eskens et al. 3. Eskens M Nguyen H Deere W et al. A retrospective evaluation of mixed energy volumetric modulated arc therapy for anal cancers with lymph node involvement.

Med Dosim. 2020; 45 (Winter): 339-345

shades more light into the usefulness of using different energies or a combination of energies for anal cancers with lymph node involvement. This is a well written paper; however, certain useful information was not addressed in the manuscript.