Assessment of Surface and Build-up Doses for a ۶ MV Photon Beam using Parallel Plate Chamber, EBT۳ Gafchromic Films, and PRIMO Monte Carlo Simulation Code

Background: Accurate assessment of surface and build-up doses has a key role in radiotherapy, especially for the superficial lesions with uncertainties involved while performing measurements in the build-up region.Objective: This study aimed to assess surface and build-up doses for ۶ MV photon beam from linear accelerator using parallel plate ionization chamber, EBT۳ Gafchromic films, and PRIMO Monte Carlo (MC) simulation code.Material and Methods: In this experimental study, parallel plate chamber (PPC۰۵) and EBT۳ Gafchromic films were used to measure doses in a build-up region for ۶ MV beam from the linear accelerator for different field sizes at various depths ranging from ۰ to ۲ cm from the surface with ۱۰۰ cm source to surface distance (SSD) in a solid water phantom. Measured results were compared with Monte Carlo simulated results using PENELOPE-based PRIMO simulation code for the same setup conditions. Effect of gantry angle incidence and SSD were also analyzed for depth doses at the surface and build-up regions using PPC۰۵ ion chamber and EBT۳ Gafchromic films.Results: Doses measured at the surface were ۱۴.۷۸%, ۱۹.۸۷%, ۲۵.۸۳%, and ۳۱.۵۴% for field sizes of ۵×۵, ۱۰×۱۰, ۱۵×۱۵, and ۲۰×۲۰ cm۲, respectively for a ۶ MV photon beam with a parallel plate chamber and ۱۴.۲۰%, ۱۹.۱۴%, ۲۵.۱۴۹%, and ۳۰.۹۰%, respectively for EBT۳ Gafchromic films. Both measurement sets were in good agreement with corresponding simulated results from the PRIMO MC simulation code; doses increase with the increase in field sizes. Conclusion: Good agreement was observed between the measured depth doses using parallel plate ionization chamber, EBT۳ Gafchromic films, and the simulated depth doses using PRIMO Monte Carlo simulation code.

Keywords:

Chamber , Dosimetry , Monte Carlo Method , Radiotherapy