Radiation dose distribution under the area protected using a Cerrobend block during external beam radiotherapy: a film study

Abstract

BACKGROUND In radiation therapy, to spare normal surrounding tissues, either Multileaf Collimators or Cerrobend blocks are used. PURPOSE The current study focuses on the relative dose distribution under the areas protected by Cerrobend blocks. MATERIALS AND METHODS A dual-energy linear accelerator and a Cobalt-60 machine were utilised as radiation sources. Several blocks were designed using commercially available materials to shield radiation fields. The relative dose distribution was then evaluated using extended dose range 2 films. RESULTS Results showed that the dose distribution under protected areas depends on several parameters including the width and height of protecting blocks, incident photon beam energy, radiation field size and source to surface distance. An increase in Cerrobend block height from 80 to 95 mm significantly decreases the dose at the protected areas. CONCLUSION An increase in the block width and photon energy decreases the relative dose deposition at the protected area. However, electron and neutron contaminations should also be taken into consideration.