Program Information
The Effect of Varying Target Size in Eclipse in Dose Calculation Accuracy for Small Fields
Y Qin*, H Zhong , N Wen , A Doemer , J Gordon , I Chetty , Henry Ford Health System, Detroit, MI
Presentations
PO-BPC-Exhibit Hall-9 (Saturday, March 7, 2015) Room: Exhibit Hall
Purpose:To investigate the dosimetric impact of varying effective target size in Eclipse on the accuracy of the AAA and AcurosXB algorithms for dose calculation of small fields, using Monte Carlo (MC) simulations and measurements.
Methods:The effective target size parameter was tuned to 0, 1, 2, and 3mm in the beam model for AAA v11 and AcurosXB v11 for the 6X Flattening Filter Free (FFF) beam of the Edge Linear Accelerator (Varian Medical System, Palo Alto, CA). Dose calculation was performed in a virtual water phantom for 4 fields: 10x10, 2x2, 1x1, and 0.5x0.5 at 100cm SSD. An IAEA-compliant phase space file generated based on camera measured spot geometry1 was set as input into the EGSnrc/BEAMnrc MC code to simulate particle transport in jaws. Subsequently, dose in the phantom was calculated using DOSXYZnrc. Gafchromic EBT3 film measurement was done at 100cm SSD, 10cm depth in solid water. Measured and MC doses were compared against calculations with varying target. Percent-depth-dose and profiles were evaluated.
Results:Agreement against MC within 2% was observed for all targets at 10x10 and 2x2 fields. Significant differences exist for field sizes less than 2x2cm2. At 0.5x0.5cm2, dose at dmax differed by 50% between target sizes of 0 and 3mm for both algorithms; dmax depth differed by 2mms. MC simulations were validated against film measurements. Varian’s recommended spot sizes in Eclipse are 0mm for AAA and 1mm for AcurosXB2. Our results show that MC simulation agrees most with AAA1mm and AcurosXB1mm. 3%/1mm Gamma analysis between AAA1mm and MC profiles at 10cm yields 92.6%(0.5x0.5cm2), 90.7%(1x1cm2), and 99.1%(2x2cm2). Between AcurosXB and MC, gamma indices are 77%(0.5x0.5cm2), 86%(1x1cm2), and 83.6%(2x2cm2).
Conclusion:Dose calculation using AAA and AcurosXB utilizing varying target sizes shows significant difference at field sizes smaller than 2x2cm2. The optimal target size is 1mm for both algorithms based on MC simulations.
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