Abstract
A commercial electron Monte Carlo (eMC) dose calculation algorithm has become available in Eclipse treatment planning system. The purpose of this work was to evaluate the eMC algorithm and investigate the clinical implementation of this system. The beam modeling of the eMC algorithm was performed for beam energies of 6, 9, 12, 16, and 20 MeV for a Varian Trilogy and all available applicator sizes in the Eclipse treatment planning system. The accuracy of the eMC algorithm was evaluated in a homogeneous water phantom, solid water phantoms containing lung and bone materials, and an anthropomorphic phantom. In addition, dose calculation accuracy was compared between pencil beam (PB) and eMC algorithms in the same treatment planning system for heterogeneous phantoms. The overall agreement between eMC calculations and measurements was within 3%/2 mm, while the PB algorithm had large errors (up to 25%) in predicting dose distributions in the presence of inhomogeneities such as bone and lung. The clinical implementation of the eMC algorithm was investigated by performing treatment planning for 15 patients with lesions in the head and neck, breast, chest wall, and sternum. The dose distributions were calculated using PB and eMC algorithms with no smoothing and all three levels of 3D Gaussian smoothing for comparison. Based on a routine electron beam therapy prescription method, the number of eMC calculated monitor units (MUs) was found to increase with increased 3D Gaussian smoothing levels. 3D Gaussian smoothing greatly improved the visual usability of dose distributions and produced better target coverage. Differences of calculated MUs and dose distributions between eMC and PB algorithms could be significant when oblique beam incidence, surface irregularities, and heterogeneous tissues were present in the treatment plans. In our patient cases, monitor unit differences of up to 7% were observed between PB and eMC algorithms. Monitor unit calculations were also preformed based on point‐dose prescription. The eMC algorithm calculation was characterized by deeper penetration in the low‐density regions, such as lung and air cavities. As a result, the mean dose in the low‐density regions was underestimated using PB algorithm. The eMC computation time ranged from 5 min to 66 min on a single 2.66 GHz desktop, which is comparable with PB algorithm calculation time for the same resolution level.PACS number: 87.55.K‐
Highlights
Electron beams are advantageous in the treatment of superficial tumors and frequently find applications in the treatment of head and neck cancers, chest wall irradiation for breast cancer, skin and lip cancers, and nodes boost
One major limitation of the pencil beam (PB) algorithm is its inaccuracy in predicting the dose in a variety of clinical situations such as perturbations by air cavities or other heterogeneities, as well as the backscatter from high-density materials such as bone.[1,2,3,4,5] Due to the limitations of the PB algorithm, electron beam isodose calculations are rarely performed in some institutions
It is widely accepted that Monte Carlo simulations are an accurate method for calculating dose distributions in radiation therapy, provided the radiation source and phantom are accurately modeled and a sufficient number of particle histories are simulated.[6,7,8,9,10,11,12,13,14,15] The superior accuracy of several Monte Carlo codes such as EGSnrc, PENELOPE, and DPM has been demonstrated for a wide range of materials and energies.[16,17,18,19,20,21] the routine use of Monte Carlo simulations for external beam radiotherapy has been impeded by the long calculation time
Summary
Electron beams are advantageous in the treatment of superficial tumors and frequently find applications in the treatment of head and neck cancers, chest wall irradiation for breast cancer, skin and lip cancers, and nodes boost. It is widely accepted that Monte Carlo simulations are an accurate method for calculating dose distributions in radiation therapy, provided the radiation source and phantom are accurately modeled and a sufficient number of particle histories are simulated.[6,7,8,9,10,11,12,13,14,15] The superior accuracy of several Monte Carlo codes such as EGSnrc, PENELOPE, and DPM has been demonstrated for a wide range of materials and energies.[16,17,18,19,20,21] the routine use of Monte Carlo simulations for external beam radiotherapy has been impeded by the long calculation time. The utilization of computer resources and variance reduction techniques makes Monte Carlo algorithm more practical for clinical situations
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