Dose Distribution Analysis for Electron Beam Irregular Fields in Treatment of Superficial Tumors: A Monte Carlo Study



Bamneshin K¹ ; Shokrani P² ; Tavakkoli MB² Show Affiliations
Source: Journal of Isfahan Medical School Published:2011

Abstract

Background: In the superficial treatment with Electron beam, the Irregular radiation fields are produced because of the shield at the end of the applicator or on the surface of the body in the treatment field. In this situation the dispersion amount in irregular fields change in comparison to the regular field and causes dosimeter value changes. Methods: In this study, in order to study the effect of the shield, the simulation code BEAMnrc based on EGSnrc, which is installed on Linux OS, was used for simulating and calculating R90 irregular fields, which were made of shielding square fields of (15*15)(20*20)(25*25) CM. For experimental measurement a type P silicon diode manufactured by Scanditronix was used. R90 simulated irregular fields were compared with dosimetric amounts gained by methods of equivalent open field and open field. Findings: The depth of R90 changed as a result of change in the shielded area and the shape of the field and there was no specific order in its increasing or decreasing. The amount of change in irregular fields with 6 mega electron volt energy compared to an equivalent field are less than 2 millimeters and compared to an open field are less than 1 millimeter. Conclusion: The study proved that using the open field method is better than the equivalent field method in measuring R90. © 2011 Isfahan University of Medical Sciences(IUMS). All rights reserved.