A Monte Carlo model of photon beams used in radiation therapy

Lovelock, David; Chui, Chen‐Shou; Mohan, Radhe

doi:10.1118/1.597620

Cited by 104 publications

(94 citation statements)

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“…energy, orientation, aperture, and wedge angle) were converted to the format accessible to the MC calculation. An energy spectrum that was derived from phase‐space data and benchmarked by measurement 17 was used instead of the nominal energy for the specific treatment machine. The incident fluence distribution was obtained by convolution of each beam aperture with the source distribution 13 The MC algorithm calculated the dose by simulating all of the radiation interactions based on a probability distribution derived from first principles.…”

Section: Methodsmentioning

confidence: 99%

Dosimetric advantage of using 6 MV over 15 MV photons in conformal therapy of lung cancer: Monte Carlo studies in patient geometries

Wang

Yorke

Desobry

et al. 2002

J Applied Clin Med Phys

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Many lung cancer patients who undergo radiation therapy are treated with higher energy photons (15‐18 MV) to obtain deeper penetration and better dose uniformity. However, the longer range of the higher energy recoil electrons in the low‐density medium may cause lateral electronic disequilibrium and degrade the target coverage. To compare the dose homogeneity achieved with lower versus higher energy photon beams, we performed a dosimetric study of 6 and 15 MV three‐dimensional (3D) conformal treatment plans for lung cancer using an accurate, patient‐specific dose‐calculation method based on a Monte Carlo technique. A 6 and 15 MV 3D conformal treatment plan was generated for each of two patients with target volumes exceeding 200 cm3 on an in‐house treatment planning system in routine clinical use. Each plan employed four conformally shaped photon beams. Each dose distribution was recalculated with the Monte Carlo method, utilizing the same beam geometry and patient‐specific computed tomography (CT) images. Treatment plans using the two energies were compared in terms of their isodose distributions and dose‐volume histograms (DVHs). The 15 MV dose distributions and DVHs generated by the clinical treatment planning calculations were as good as, or slightly better than, those generated for 6 MV beams. However, the Monte Carlo dose calculation predicted increased penumbra width with increased photon energy resulting in decreased lateral dose homogeneity for the 15 MV plans. Monte Carlo calculations showed that all target coverage indicators were significantly worse for 15 MV than for 6 MV; particularly the portion of the planning target volume (PTV) receiving at least 95% of the prescription dose false(V95false) dropped dramatically for the 15 MV plan in comparison to the 6 MV Spinal cord and lung doses were clinically equivalent for the two energies. In treatment planning of tumors that abut lung tissue, lower energy (6 MV) photon beams should be preferred over higher energies (15–18 MV) because of the significant loss of lateral dose equilibrium for high‐energy beams in the low‐density medium. Any gains in radial dose uniformity across steep density gradients for higher energy beams must be weighed carefully against the lateral beam degradation due to penumbra widening.PACS number(s): 87.90.+y, 87.52.–g

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Section: Methodsmentioning

confidence: 99%

Dosimetric advantage of using 6 MV over 15 MV photons in conformal therapy of lung cancer: Monte Carlo studies in patient geometries

Wang

Yorke

Desobry

et al. 2002

J Applied Clin Med Phys

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“…Recently, application of Monte Carlo simulation has experienced tremendous growth, particularly in studying clinical accelerators. [13][14][15][16] This is because Monte Carlo simulation enables us to study the accelerator at a greater depth in identifying individual sources of the backscatter from collimator jaws. The motivation for this work is to model the backscattered radiation as functions of the upper ͑Y͒ and lower ͑X͒ jaw positions.…”

Section: Introductionmentioning

confidence: 99%

Modeling photon output caused by backscattered radiation into the monitor chamber from collimator jaws using a Monte Carlo technique

2000

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Dose per monitor unit in photon fields generated by clinical linear accelerators can be affected by the backscattered radiation into the monitor chamber from collimator jaws. Thus, it is necessary to account for the backscattered radiation in computing monitor unit setting for a treatment field. In this work, we investigated effects of the backscatter from collimator jaws based on Monte Carlo simulations of a clinical linear accelerator. The backscattered radiation scored within the monitor chamber was identified as originating either from the upper jaws ͑Y jaws͒, or from the lower jaws ͑X jaws͒. From the results of Monte Carlo simulations, ratios of the monitor-chamber-scored dose caused by the backscatter to the dose caused by the forward radiation, R(x,y), were modeled as functions of the individual X and Y jaw positions. The amount of the backscattered radiation for any field setting was then computed as a compound contribution from both the X and Y jaws. The dose ratios of R(x,y) were then used to calculate the change in photon output caused by the backscatter, S cb (x,y). Results of these calculations were compared with available measured data based on counting the electron pulses or charge from the electron target of an accelerator. Data from this study showed that the backscattered radiation contributes approximately 3% to the monitorchamber-scored dose. A majority of the backscattered radiation comes from the upper jaws, which are located closer to the monitor chamber. The amount of the backscatter decreases approximately in a linear fashion with the jaw opening. This results in about a 2% increase of photon output from a 10 cmϫ10 cm field to a 40 cmϫ40 cm field. The off-axis location of the jaw opening does not have a significant effect on the magnitude of the backscatter. The backscatter effect is significant for monitor chambers using kapton windows, particularly for treatment fields using moving jaws. Applying the backscatter correction improves the accuracy of monitor-unit calculation using a model-based dose calculation algorithm such as the convolution method. © 2000 American Association of Physicists in Medicine. ͓S0094-2405͑00͒00904-4͔

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“…The electron beam incident upon the target is modeled as a parallel circular beam with a 0.1 cm radius. ( 9 , 20 ) The incident electrons possessed an energy distribution with a Gaussian outline with a center at 6.5 MeV for 6 MV beam and FWHM of 0.5 MeV (Varian Oncology Systems Ltd.). As with the study by Siebers et al, ( 19 ) the photon energy transport cutoff was set to 0.01 MeV, while the electron kinetic energy cutoff was 0.189 MeV.…”

Section: Methodsmentioning

confidence: 99%

“…( 9 , 10 ) Each of these works used EGS4‐based Monte Carlo transport. Calculations of the PSD and the patient dependent portion of the beam line have been performed using the BEAM user code, ( 11 ) too.…”

Section: Introductionmentioning

confidence: 99%

Suggesting a new design for multileaf collimator leaves based on Monte Carlo simulation of two commercial systems

Hariri

Shahriari

2010

J Applied Clin Med Phys

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Due to intensive use of multileaf collimators (MLCs) in clinics, finding an optimum design for the leaves becomes essential. There are several studies which deal with comparison of MLC systems, but there is no article with a focus on offering an optimum design using accurate methods like Monte Carlo. In this study, we describe some characteristics of MLC systems including the leaf tip transmission, beam hardening, leakage radiation and penumbra width for Varian and Elekta 80‐leaf MLCs using MCNP4C code. The complex geometry of leaves in these two common MLC systems was simulated. It was assumed that all of the MLC systems were mounted on a Varian accelerator and with a similar thickness as Varian's and the same distance from the source. Considering the obtained results from Varian and Elekta leaf designs, an optimum design was suggested combining the advantages of three common MLC systems and the simulation results of this proposed one were compared with the Varian and the Elekta. The leakage from suggested design is 29.7% and 31.5% of the Varian and Elekta MLCs. In addition, other calculated parameters of the proposed MLC leaf design were better than those two commercial ones. Although it shows a wider penumbra in comparison with Varian and Elekta MLCs, taking into account the curved motion path of the leaves, providing a double focusing design will solve the problem. The suggested leaf design is a combination of advantages from three common vendors (Varian, Elekta and Siemens) which can show better results than each one. Using the results of this theoretical study may bring about superior practical outcomes.PACS number: 87.56.nk, 87.55.K, 87.56.N

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A Monte Carlo model of photon beams used in radiation therapy

Cited by 104 publications

References 0 publications

Dosimetric advantage of using 6 MV over 15 MV photons in conformal therapy of lung cancer: Monte Carlo studies in patient geometries

Dosimetric advantage of using 6 MV over 15 MV photons in conformal therapy of lung cancer: Monte Carlo studies in patient geometries

Modeling photon output caused by backscattered radiation into the monitor chamber from collimator jaws using a Monte Carlo technique

Suggesting a new design for multileaf collimator leaves based on Monte Carlo simulation of two commercial systems

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