Design and evaluation of electron beam energy degraders for breast boost irradiation

Abstract

BackgroundFor breast cancer patients who require electron boost energies between 6 and 9 MeV, an energy degraders (ED) in the 9 MeV beamline was specially designed and manufactured to increase the skin dose of 6 MeV and to reduce the penetration depth of 9 MeV beams.MethodsWe used Monte Carlo (MC) techniques as a guide in the design of ED for use with linear accelerators. In order to satisfy percent depth dose (PDD) characteristics and dose profile uniformity in water, the shape and thickness of Lucite® ED in the 9 MeV beamline was iteratively optimized and then manufactured. The ED geometry consists of a truncated cone attached on top of a plane plate, with total central thickness of 1.0 cm. The ED was placed on the lower most scraper of the electron applicator. The PDDs, profiles, and output factors were measured in water to validate the MC-based design.ResultsSkin doses with the EDs increased by 8–9 %, compared to those of the 9 MeV beam. The outputs with the EDs were 0.882 and 0.972 for 10 × 10 and 15 × 15 cm2 cones, respectively, as compared to that of a conventional 9 MeV beam for a 10 × 10 cm2 cone. The X-ray contamination remained less than 1.5 %. In-vivo measurements were also performed for three breast boost patients and showed close agreement with expected values.ConclusionsThe optimally designed ED in the 9 MeV beamline provides breast conserving patients with a new energy option of 7 MeV for boost of the shallow tumor bed. It would be an alternative to bolus and thus eliminate inconvenience and concern about the daily variation of bolus setup.

Influence of 3D-printed collimator thickness on near-the-edge scattering of high-energy electrons

“…They demonstrated that the percent horn relative to the central axis decreases when size of the field entering the applicator approaches the collimation hole size and increases with growing beam energy [24]. Park et al [25] and Northey et al [26], moreover, performed numerical simulations modeling the parameters of energy degraders [25] and plastic inserts [26] that are necessary to lower the dose profile horns and reach the predetermined field homogeneity level. They found that optimally shaped additional forming samples provide control of radiation field parameters such as penetration and flatness.…”