Perturbation of irradiated dose by treatment couch

Chu, S S; Choi, B S; Lee, D H

Abstract

The perturbation of dose distribution and attenuation by back plate and metal frame of treatment couch incobalt-60 teletherapy unit, Toshiba RCA-120-1. 4,000 Ci, was measured by various detectors and industrial film andprevented by using the styrofoam bed during irradiation as full rotation or four portal oblique technique. 1.Shielding the primary gamma ray beam by metal frame of treatment couch, the irradiated radiation dose wasattenuated about 40-70%. 2. The tumor center dose due to shielding with back plate of treatment couch duringirradiation as four portal oblique combination was attenuated 20-50% according to patients thickness. 3. The doseattenuation by 1cm acryl plate was about 3% and the back skin surface get to the build up equilibrium state bysecondary radiation from acry plate, therefor the advantage of skin sparing effect from high energy photonirradiation could not expected. 4. Situated the treatment couch between the source and tumor center, about 10-20%attenuation of full rotation dose was occured. 5. Using the styrofoam bad, air equivalent material, physicaldensity, =0.0015 and half value layer for cobalt-60 gamma ray, HVL=1.2x104cm, the attenuation of irradiated dosedue to shielding of back plate and metal frame from treatment couch was completely prevented during rotation orfour portal oblique irradiation.