Program Information
Comparison of Output Factors for Small Radiation Fields Used in SBRT Treatment
R Gupta*, A Eldib , J Li , C Ma , Fox Chase Cancer Center, Philadelphia, PA
Presentations
SU-F-T-610 (Sunday, July 31, 2016) 3:00 PM - 6:00 PM Room: Exhibit Hall
Purpose:In order to fundamentally understand our previous dose verification results between measurements and calculations from treatment planning system (TPS) for SBRT plans for different sized targets, the goal of the present work was to compare output factors for small fields measured using EDR2 films with TPS and Monet Carlo (MC) simulations.
Methods:6MV beam was delivered to EDR2 films for each of the following field sizes; 1x1 cm², 1.5x1.5 cm², 2x2 cm², 3x3 cm², 4x4 cm², 5x5 cm² and 10x10 cm². The films were developed in a film processer, then scanned with a Vidar VXR-16 scanner and analyzed using RIT113 version 6.1. A standard calibration curve was obtained with the 6MV beam and was used to get absolute dose for measured field sizes. Similar plans for all fields sizes mentioned above were generated using Eclipse with the Analytical Anisotropic Algorithm. Similarly, MC simulations were carried out using the MCSIM, an in-house MC code for different field sizes. Output factors normalized to 10x10 cm² reference field were calculated for different field sizes in all the three cases and compared.
Results:For field sizes ranging from 1x1 cm² to 2x2 cm², the differences in output factors between measurements (films), TPS and MC simulations were within 0.22%. For field sizes ranging from 3x3cm² to 5x5cm², differences in output factors were within 0.10%.
Conclusion:No clinically significant difference was obtained in output factors for different field sizes acquired from films, TPS and MC simulations. Our results showed that the output factors are predicted accurately from TPS when compared to the actual measurements and superior dose calculation Monte Carlo method. This study would help us in understanding our previously obtained dose verification results for small fields used in the SBRT treatment.
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