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Feasibility of Using Monte-Carlo Based Treatment Planning System to Calculate Output Factors for Patients Receiving Electron Radiation Therapy

H Xu

S Mossahebi , H Xu*, P Aryal , N Lamichhane , M Guerrero , B Yi , K Prado , S Chen , Univ. of Maryland School Of Medicine, Baltimore, MD


SU-I-GPD-T-65 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: For patients receiving electron radiation therapy with dimension of cutout less than the half of electron energy, the standard practice is to perform the cutout factor measurement. RayStation v5.0 electron Monte Carlo algorithm provides a way to calculate cutout factors instead of measurements. This study evaluates the accuracy of RayStation Monte Carlo for cutout factor calculations.

Methods: Twenty five cutout blocks with cutout sizes of 20×20, 15×15, 10×10, 6×6, 4×4, and 3×3 were made for respective electron applicators. The dose was of same MU calculated with RayStation v5.0 treatment planning system for open cones and the 25 cutout in a water phantom for all electron energies (6, 9 12, 16, 20 MeV) at the depth of maximum dose of each cutout, and the cutout factor was calculated as the ratio of cutout to open field calculated doses. The cutout factor was also measured in the water phantom with a CC-04 ion-chamber. The measurements were compared to calculated cutout factors. The algorithm was also validated using 2 clinical electron patient cutout.

Results: RayStation Cone factor calculations were within 1% agreement with ion chamber measurements for all energies. Cutout factor calculations were within 3% agreement with measurement for 6, 9, 12, 16 MeV. For 20 MeV and small cutouts (smaller than half of cone size) the disagreement can be up to 6% (3×3 cutout in 25×25 cone size). For two clinical cutouts the calculated point doses were within 1% agreement with measurements.

Conclusion: Output factors calculations of RayStation electron Monte Carlo are clinically acceptable for standard treatment. Caution should be paid for high energy (20 MeV) when small cutout size is utilized.

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