(Monday, 7/15/2019) 3:45 PM - 4:15 PM
Room: Exhibit Hall | Forum 1
Purpose: To validate RayStation Monte Carlo (MC) dose calculation for electron treatment planning.
Methods: The doses/MUs calculated by RayStation v6.1 MC dose engine are compared to hand calculated doses/MUs using beam data. Several scenarios are verified for standard/extended SSDs, normal/oblique incident angles and direct lead-on-skin collimation. MC calculated dose distributions were validated by GAFCHROMIC EBT3 film dosimetry for oblique beam angles, clinical cutouts, and at bone/lung/water interface with a heterogeneous phantom using tissue equivalent bone/lung slabs from CIRS at various depths.
Results: The RMS % differences between calculated and measured PDDs are within 2.4% and 0.8% for buildup and falloff region respectively. Comparing to hand calculated MUs, the MC calculated MUs are within 1.3% at 100cm SSD and 2.6% at 110cm SSD for all energies/open cone combinations, and 2.2% for any energies/cone/cutout combinations, even with the present of bolus and lead cutout on skin, as far as lateral electron equilibrium is preserved. MU differences are within 3% for any clinically used energy/cone/cutout combinations with cone cutout size down to 3x3 cm, or skin cutout size down to 2.5cm with or without bolus. For film results in homogenous phantom, MC absolute dose agreement is better than 95% passing rate for 3%/3mm/TH10% criteria for all cases including oblique incidence up to 30 degree. For clinical cutouts, the MC results are better than 99.2% except for the largest cutout, which passed at 94.5%/90%/91.8% for 12MeV/15Mev/18Mev. For the heterogeneous phantom results, the relative passing rate is 96.1% with 2% norm point difference for all energies and depths except for 6 Mev at 1.5cm and 18 Mev at 2cm, which passed at 90.9%/94.4% with 5% norm point difference, using 3%/3mm/TH10% criteria.
Conclusion: The successful implementation of electron MC dose calculation eliminated time-consuming measurements and facilitated accurate dosimetry for cases with heterogeneity or without electron equilibrium.
Keywords
Monte Carlo, Radiochromic Film
Taxonomy
Not Applicable / None Entered.
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