Abstract
Accurate dose measurement in the buildup region is extremely difficult. Studies have reported that treatment planning systems (TPS) cannot calculate surface dose accurately. The aim of the study was to compare the film measurements and TPS calculations for surface dose in head and neck cancer treatment using intensity modulated radiation therapy (IMRT). IMRT plans were generated for 5 head and neck cancer patients by using Varian Eclipse TPS. Quality assurance (QA) plans of these IMRT plans were created on rando phantoms for surface dose measurements. EBT3 films were cut in size of 2.5 x 2.5 cm 2 and placed on the left side, right side and the center of larynx and then the films were irradiated with 6 MV photon beams. The measured doses were compared with TPS. The results of TPS calculations were found to be lower compared to the EBT3 film measurements at all selected points. The lack of surface dose calculation in TPS should be considered while evaluating the radiotherapy plans.
Highlights
The dose deposited between air and phantom is defined as the surface dose
The surface doses were found to be higher with Gafchromic EBT3 film compared to Eclipse treatment planning systems (TPS) for all points
In this study film measurements and TPS calculations compared in 10x10 cm2 open field
Summary
The dose deposited between air and phantom is defined as the surface dose. Surface dose measurement is a challenging issue, due to steep dose reduction in surface area because of the absence of electron equilibrium. This steep dose gradient is causing requirement of special measurement techniques with appropriate dosimetric devices. The most accurate dosimetric device for surface dose measurement is extrapolation ionization chamber, yet it is not owned in all institutes. Parallel plate ionization chambers can be used after making Gerbi’s overresponse corrections [2]. The overresponse occurs because of the scattering electrons from the sidewall of the parallel plate chamber. The physical properties of these chambers confine the usage with only phantom measurements
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