Clinical Implementation of Electron Energy Changes of Varian Linear Accelerators

Abstract

Modern dual (photon) energy linear accelerators often comes with a limited selection of electron beams. The high-energy electron beam has limited range and relative sharp distal falloff in its depth dose curve compared to that of high-energy photon beams. Its radiation dose is often delivered appositionally to cover the target volume to its distal 90% depth dose (d90), while avoiding the normal, sometimes critical structure, immediately distal to the target.  The intermediate electron energy is often needed for optimal dose distribution. In this study we investigated electron beam characteristics and implemented two new electron beams on two Varian linear accelerators. Comprehensive tests and measurements indicated the new electron beams met all dosimetry parameter criteria and operational safety standards.  With these two new electron beams in addition to existing electron beams we were able to provide a choice of electron beams which had d90depth between 1.5 cm and 6.0 cm and from 1.5 cm to 4.0 cm in 0.5 cm increment to meet our clinical need.