Monte Carlo and analytic modeling of an Elekta Infinity linac with Agility MLC: Investigating the significance of accurate model parameters for small radiation fields

Abstract

PurposeTo explain the deviation observed between measured and Monaco calculated dose profiles for a small field (i.e., alternating open‐closed MLC pattern). A Monte Carlo (MC) model of an Elekta Infinity linac with Agility MLC was created and validated against measurements. In addition, an analytic model which predicts the fluence at the isocenter plane was used to study the impact of multiple beam parameters on the accuracy of dose calculations for small fields.MethodsA detailed MC model of a 6 MV Elekta Infinity linac with Agility MLC was created in EGSnrc/BEAMnrc and validated against measurements. An analytic model using primary and secondary virtual photon sources was created and benchmarked against the MC simulations and the impact of multiple beam parameters on the accuracy of the model for a small field was investigated. Both models were used to explain discrepancies observed between measured/EGSnrc simulated and Monaco calculated dose profiles for alternating open‐closed MLC leaves.Results MC‐simulated dose profiles (PDDs, cross‐ and in‐line profiles, etc.) were found to be in very good agreements with measurements. The best fit for the leaf bank rotation was found to be 9 mrad to model the defocusing of Agility MLC. Moreover, a very good agreement was observed between results from the analytic model and MC simulations for a small field. Modifying the radial size of the incident electron beam in the BEAMnrc model improved the agreement between Monaco and EGSnrc calculated dose profiles by approximately 16% and 30% in the position of maxima and minima, respectively.ConclusionAccurate modeling of the full‐width‐half‐maximum (FWHM) of the primary photon source as well as the MLC leaf design (leaf bank rotation, etc.) is essential for accurate calculations of dose delivered by small radiation fields when using virtual source or MC models of the beam.

Investigation of pixel scale calibration on the Elekta iView electronic portal imager

“…Alternatively, this result may be due to the use of Elekta linear accelerators, which have been suggested to display a wider focal spot in the crossplane direction relative to in-plane. 11,12 This would cause a wider cross-plane beam penumbra, increasing the number of pixels measured, and a correspondingly smaller pixel scale factor which is consistent with the study findings. Change in pixel scale factor with SSD followed a predictable linear trend, varying by 0.00025 mm/pixel for each millimeter error in SSD.…”

Design and Evaluation of Structural Shielding of a Typical Radiotherapy Facility Using EGSnrc Monte Carlo Code

“…Based on the previous studies, MC simulation has been considered to be the most accurate tool to describe the underlying physical interactions between radiation and matter. EGSnrc MC Software has been successfully used in various dosimetry principles,[ 12 13 ] HVL evaluation of orthovoltage machine,[ 14 ] simulation of radiotherapy treatment units,[ 15 16 17 18 ] beam quality correction factor,[ 19 ] and so forth. Furthermore, previous studies have shown that MC can be used in the evaluation of X-rays transmission through some shielding materials,[ 11 ] evaluation of the attenuation coefficient of personal radiation shielding protective clothing,[ 20 ] determination of shielding properties of concrete,[ 21 ] shielding analysis,[ 22 ] and the simulation of X-ray room shielding in diagnostic radiology.…”

Monte Carlo modeling of the Elekta Versa HD and patient dose calculation with EGSnrc/BEAMnrc

“…There have been previous groups to model Elekta's 160 leaf Agility collimator. [27][28][29] However, to the best of our knowledge, there is currently no model of Elekta's Versa HD linear accelerator that can be used for routine dose calculation on patients' CT datasets. We have developed a method for routine, independent patient dose calculations from treatment plans generated in a commercial TPS with our own Monte Carlo model.…”