Abstract
The purpose of this study is to evaluate the accuracy of the electron Monte Carlo (eMC) dose calculation algorithm included in a commercial treatment planning system and compare its performance against an electron pencil beam algorithm. Several tests were performed to explore the system's behavior in simple geometries and in configurations encountered in clinical practice. The first series of tests were executed in a homogeneous water phantom, where experimental measurements and eMC‐calculated dose distributions were compared for various combinations of energy and applicator. More specifically, we compared beam profiles and depth‐dose curves at different source‐to‐surface distances (SSDs) and gantry angles, by using dose difference and distance to agreement. Also, we compared output factors, we studied the effects of algorithm input parameters, which are the random number generator seed, as well as the calculation grid size, and we performed a calculation time evaluation. Three different inhomogeneous solid phantoms were built, using high‐ and low‐density materials inserts, to clinically simulate relevant heterogeneity conditions: a small air cylinder within a homogeneous phantom, a lung phantom, and a chest wall phantom. We also used an anthropomorphic phantom to perform comparison of eMC calculations to measurements. Finally, we proceeded with an evaluation of the eMC algorithm on a clinical case of nose cancer. In all mentioned cases, measurements, carried out by means of XV‐2 films, radiographic films or EBT2 Gafchromic films. were used to compare eMC calculations with dose distributions obtained from an electron pencil beam algorithm. eMC calculations in the water phantom were accurate. Discrepancies for depth‐dose curves and beam profiles were under 2.5% and 2 mm. Dose calculations with eMC for the small air cylinder and the lung phantom agreed within 2% and 4%, respectively. eMC calculations for the chest wall phantom and the anthropomorphic phantom also showed a positive agreement with the measurements. The retrospective dosimetric comparison of a clinical case, which presented scatter perturbations by air cavities, showed a difference in dose of up to 20% between pencil beam and eMC algorithms. When comparing to the pencil beam algorithm, eMC calculations are definitely more accurate at predicting large dose perturbations due to inhomogeneities.PACS numbers: 87.55.de, 87.55.kd
Highlights
Monte Carlo (MC) techniques are widely used in radiotherapy to simulate the propagation of photons and charged particles through matter.[1,2,3] MC algorithms are considered to be the ultimate treatment planning dose calculation tool
The purpose of this study is to evaluate the accuracy of the electron Monte Carlo dose calculation algorithm included in a commercial treatment planning system and compare its performance against an electron pencil beam algorithm
The first series of tests were executed in a homogeneous water phantom, where experimental measurements and electron Monte Carlo (eMC)-calculated dose distributions were compared for various combinations of energy and applicator
Summary
Monte Carlo (MC) techniques are widely used in radiotherapy to simulate the propagation of photons and charged particles through matter.[1,2,3] MC algorithms are considered to be the ultimate treatment planning dose calculation tool. The electron Monte Carlo (eMC) dose calculation algorithm included in the Eclipse treatment planning system (Varian, Palo Alto, CA) is a fast implementation of the Monte Carlo method used for computation of dose, from high-energy electron beam. It is based on standard EGS Monte Carlo methods[5] and reduces the processing time by introducing simplifications to the calculation algorithm. The system’s behavior of this commercial product has previously been studied,(6,7,8) and ionization chamber dosimetry, film dosimetry, and Monte Carlo simulations were used to validate dose distributions with the eMC algorithm. A calculation time evaluation was performed to validate the clinical viability of this commercial product, especially since the introduction of the Distributed Calculation Framework that permits parallelized dose calculation
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