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Development of An Independent, Monte Carlo, Dose Calculation, Quality Assurance Tool for Clinical Trials

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A Faught

A Faught1,2*, S Davidson3 , S Kry1 , J Fontenot4 , C Etzel1,5 , G Ibbott1 , D Followill1 , (1) UT MD Anderson Cancer Center, Houston, TX, (2) University of Texas Health Science Center Houston, Graduate School of Biomedical Sciences, Houston, Texas, (3) University of Texas Medical Branch of Galveston, Galveston, Texas, (4) Mary Bird Perkins Cancer Center, Baton Rouge, LA, (5) Consortium of Rheumatology Researchers of North America (CORRONA), Inc., Southborough, MA


SU-E-T-110 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose: To commission a multiple-source Monte Carlo model of Elekta linear accelerator beams of nominal energies 6MV and 10MV.

Methods: A three source, Monte Carlo model of Elekta 6 and 10MV therapeutic x-ray beams was developed. Energy spectra of two photon sources corresponding to primary photons created in the target and scattered photons originating in the linear accelerator head were determined by an optimization process that fit the relative fluence of 0.25 MeV energy bins to the product of Fatigue-Life and Fermi functions to match calculated percent depth dose (PDD) data with that measured in a water tank for a 10x10cm2 field. Off-axis effects were modeled by a 3rd degree polynomial used to describe the off-axis half-value layer as a function of off-axis angle and fitting the off-axis fluence to a piecewise linear function to match calculated dose profiles with measured dose profiles for a 40x40cm2 field. The model was validated by comparing calculated PDDs and dose profiles for field sizes ranging from 3x3cm2 to 30x30cm2 to those obtained from measurements. A benchmarking study compared calculated data to measurements for IMRT plans delivered to anthropomorphic phantoms.

Results: Along the central axis of the beam 99.6% and 99.7% of all data passed the 2%/2mm gamma criterion for 6 and 10MV models, respectively. Dose profiles at depths of dmax, through 25cm agreed with measured data for 99.4% and 99.6% of data tested for 6 and 10MV models, respectively. A comparison of calculated dose to film measurement in a head and neck phantom showed an average of 85.3% and 90.5% of pixels passing a 3%/2mm gamma criterion for 6 and 10MV models respectively.

Conclusion: A Monte Carlo multiple-source model for Elekta 6 and 10MV therapeutic x-ray beams has been developed as a quality assurance tool for clinical trials.

Funding Support, Disclosures, and Conflict of Interest: This work was funded in part by grants CA10953 and CA81647 (NCI, DHHS)

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