Conversión de un Clinac de fotones a electrones de 6 MeV para pruebas del dispositivo Converay

J. GUARDA; F. LEYTON; J. LEIVA; J. VELÁSQUEZ; M. VALENTE; F. MALANO; R. FIGUEROA

Concepción

Congreso; Tercer Congreso de la sociedad de Fiísica Médica de Chile y 7mo Congreso de Física Médica en La frontera; 2021

SOFIMECH & UFRO

This work reports on the modifications to a 6 MV photon clinac to obtain a monochromatic electronbeam. The W target of a VARIAN 600C electron accelerating guide was replaced by a 50 μm thickBe window. The modified guide was installed in a CLINAC 6-100. A new electron-gun filamentpower connector was designed and manufactured, adjusting the linac operational parameters asrequired by the replaced filament, and also removing the photon flattening filter and monitoringchambers, among other elements. Remarkably, safety has not been compromised.The linac magnetron was re-tuned according to the replaced waveguide, which was accomplishedby monitoring different electrical signals to surpass the lack of target current and monitor units.After the modifications, the emergent electron beam output has been successfully attained, and theelectrons now travel to the linac head exit, where a novel convergent beam device (conVeray®) willbe installed.Direct measurements of the electron beam were performed using Gafchromic EBT3 films,processed with an Epson Perfection V370 photo scanner, obtaining results showing a divergentconical spatial distribution instead of a pencil-beam.A virtual model was developed based on FLUKA Monte Carlo code to be used as reference duringthe device design and testing phases. The characterization of the electron beam aperture at differentdistances along with effective energy assessments have been accomplished to perform furtherdeflection experiments for the conVeray® project, obtaining (5.83 ± 0.05) MeV at the isocenterand transversal beam size around (3,615 ± 0,015) mm, that represents a 1.8° divergence. In practice,achieving such electron divergence requires a magnetic focusing system, which is being prepared.In summary, converting a standard photon mode linac to produce an emergent electron beamrequired strong technical and scientific skills, along with non-conventional solutions to overcomethe challenges to achieve a functional convergent beam device.