Program Information
Validation of the MCNPX Monte Carlo Model of the Ocular Beam Line at the Proton Therapy Center Houston
U Titt*, K Suzuki , The Univ. of Texas MD Anderson Cancer Center, Houston, TX
Presentations
SU-E-T-794 (Sunday, July 12, 2015) 3:00 PM - 6:00 PM Room: Exhibit Hall
Purpose: The PTCH is preparing the ocular proton beam nozzle for clinical use. Currently commissioning measurements are being performed using films, diodes and ionization chambers. In parallel, a Monte Carlo model of the beam line was created for integration into the automated Monte Carlo treatment plan computation system, MC². This work aims to compare Monte Carlo predictions to measured proton doses in order to validate the Monte Carlo model.
Methods: A complete model of the double scattering ocular beam line has been created and is capable of simulating proton beams with a comprehensive set of beam modifying devices, including eleven different range modulator wheels. Simulations of doses in water were scored and compare to ion chamber measurements of depth doses, lateral dose profiles extracted from half beam block exposures of films, and diode measurements of lateral penumbrae at various depths.
Results: All comparison resulted in an average relative entrance dose difference of less than 3% and peak dose difference of less than 2%. All range differences were smaller than 0.2 mm. The differences in the lateral beam profiles were smaller than 0.2 mm, and the differences in the penumbrae were all smaller than 0.4%.
Conclusion: All available data shows excellent agreement of simulations and measurements. More measurements will have to be performed in order to completely and systematically validate the model. Besides simulating and measuring PDDs and lateral profiles of all remaining range modulator wheels, the absolute dosimetry factors in terms of number of source protons per monitor unit have to be determined.
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