TU-D-224C-05: Validation of a Linear Accelerator Source Model and Commissioning Process for Routine Clinical Monte Carlo Calculations

Cui, Jing; Zakaryan, K.; Alaly, J; Vićić, M.; Wiesmeyer, Mark; Deasy, J

doi:10.1118/1.2241563

Cited by 1 publication

(5 citation statements)

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“…Leaf transmission, interleaf leakage, and rounded leaf ends were modeled as part of the fluence map. 11,16,17…”

Section: A Source Modelmentioning

confidence: 99%

“…All fitting parameters were determined at once using an automated optimization process for the specific linac model and linac energy based on the 10×10 cm field size by setting parameter boundary conditions and minimizing the differences between the measured and calculated percent depth dose (PDD) curve and dose profiles. 11,16,17 Three parameters formed the shape of the primary energy spectrum function. 11 One parameter reduced the scale of the primary spectrum to construct the extra-focal energy spectrum.…”

Section: B Commissioningmentioning

confidence: 99%

“…Cui et al has shown that repeating the commissioning process by tightening the parameter boundary conditions in an iterative fashion may improve the accuracy of the dose calculation. 16,17 However this was found to be inefficient and did not yield satisfactory results. Instead, the initial commissioned model used in this work was improved by applying a hyperbolic function to correct for the difference between the calculated and measured output based on field size.…”

Section: B Commissioningmentioning

confidence: 99%

“…36 The standard deviation of the Gaussian kernel was one of the seven parameters determined in the model optimization commissioning process. 16,17 The agreement of the calculated data with the measured data (PDDs and dose profiles) for field sizes from 4 × 4 to 40 × 40 cm 2 was tested using a gamma criterion 37 of ±2% of the maximum dose along the central axis and ±2 mm distance to agreement (DTA). In addition, local dose differences were studied for PDD and dose profiles.…”

Section: C Validation Testingmentioning

confidence: 99%

“…Specifically, a parameterized multisource model was derived from a standard set of measurements for the Varian 2100 series linac (Varian Medical Systems, Inc., Palo Alto, CA) 6 and 10 MV photon beams. 11,16,17 The source model coupled to the dose planning method (DPM) Monte Carlo method 12 provided a unique and accurate solution for addressing the problem of multiple institutions reporting dose distributions using various TPSs. Further, the analytical model approach provides a generic way to extend the model to other linacs regardless of manufacturer or model type.…”

Section: Introductionmentioning

confidence: 99%

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Purpose: A dose calculation tool, which combines the accuracy of the dose planning method (DPM) Monte Carlo code and the versatility of a practical analytical multisource model, which was previously reported has been improved and validated for the Varian 6 and 10 MV linear accelerators (linacs). The calculation tool can be used to calculate doses in advanced clinical application studies. One shortcoming of current clinical trials that report dose from patient plans is the lack of a standardized dose calculation methodology. Because commercial treatment planning systems (TPSs) have their own dose calculation algorithms and the clinical trial participant who uses these systems is responsible for commissioning the beam model, variation exists in the reported calculated dose distributions. Today's modern linac is manufactured to tight specifications so that variability within a linac model is quite low. The expectation is that a single dose calculation tool for a specific linac model can be used to accurately recalculate dose from patient plans that have been submitted to the clinical trial community from any institution. The calculation tool would provide for a more meaningful outcome analysis. Methods: The analytical source model was described by a primary point source, a secondary extra-focal source, and a contaminant electron source. Off-axis energy softening and fluence effects were also included. The additions of hyperbolic functions have been incorporated into the model to correct for the changes in output and in electron contamination with field size. A multileaf collimator (MLC) model is included to facilitate phantom and patient dose calculations. An offset to the MLC leaf positions was used to correct for the rudimentary assumed primary point source.Results: Dose calculations of the depth dose and profiles for field sizes 4 × 4 to 40 × 40 cm agree with measurement within 2% of the maximum dose or 2 mm distance to agreement (DTA) for 95% of the data points tested. The model was capable of predicting the depth of the maximum dose within 1 mm. Anthropomorphic phantom benchmark testing of modulated and patterned MLCs treatment plans showed agreement to measurement within 3% in target regions using thermoluminescent dosimeters (TLD). Using radiochromic film normalized to TLD, a gamma criteria of 3% of maximum dose and 2 mm DTA was applied with a pass rate of least 85% in the high dose, high gradient, and low dose regions. Finally, recalculations of patient plans using DPM showed good agreement relative to a commercial TPS when comparing dose volume histograms and 2D dose distributions. Conclusions: A unique analytical source model coupled to the dose planning method Monte Carlo dose calculation code has been modified and validated using basic beam data and anthropomorphic phantom measurement. While this tool can be applied in general use for a particular linac model, specifically it was developed to provide a singular methodology to independently assess treatment

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“…Leaf transmission, interleaf leakage, and rounded leaf ends were modeled as part of the fluence map. 11,16,17…”

Section: A Source Modelmentioning

confidence: 99%