Technical Note: Study of the electron transport parameters used in penelope for the Monte Carlo simulation of Linac targets. Issue 6 (18th May 2015)

• Record Type: Journal Article
• Authors: Rodriguez, Miguel; Sempau, Josep; Brualla, Lorenzo
• Is Part Of: Medical physics. Volume 42:Issue 6(2015)Part 1
• Page Start: 2877
• Page End: 2881
• Publication Date: 2015-05-18
• Subjects: dosimetry -- electron transport theory -- linear accelerators -- Monte Carlo methods -- phantoms; Dose‐volume analysis -- Monte Carlo methods; Linear accelerators -- Scintigraphy; PENELOPE -- step length -- Monte Carlo -- linac target -- Bremsstrahlung; Linear accelerators -- Photons -- Collisional energy loss -- Electron beams -- Monte Carlo methods -- Elastic collisions -- Electronic transport -- Tungsten -- Elasticity -- Positrons; Medical physics -- Periodicals; Medical physics; Geneeskunde; Natuurkunde; Toepassingen; Biophysics; Periodicals; Periodicals; Electronic journals; 610.153
• DOI: 10.1118/1.4916686
• Languages: English
• ISSNs: 0094-2405

Abstract

Abstract : Purpose: The Monte Carlo simulation of electron transport in Linac targets using the condensed history technique is known to be problematic owing to a potential dependence of absorbed dose distributions on the electron step length. In thepenelope code, the step length is partially determined by the transport parameters C 1 and C 2. The authors have investigated the effect on the absorbed dose distribution of the values given to these parameters in the target. Methods: A monoenergetic 6.26 MeV electron pencil beam from a point source was simulated impinging normally on a cylindrical tungsten target. Electrons leaving the tungsten were discarded. Radial absorbed dose profiles were obtained at 1.5 cm of depth in a water phantom located at 100 cm for values of C 1 and C 2 in the target both equal to 0.1, 0.01, or 0.001. A detailed simulation case was also considered and taken as the reference. Additionally, lateral dose profiles were estimated and compared with experimental measurements for a 6 MV photon beam of a Varian Clinac 2100 for the cases of C 1 and C 2 both set to 0.1 or 0.001 in the target. Results: On the central axis, the dose obtained for the case C 1 = C 2 = 0.1 shows a deviation of (17.2% ± 1.2%) with respect to the detailed simulation. This difference decreases to (3.7% ± 1.2%) for the case C 1 = C 2 = 0.01. The case C 1 = C 2 = 0.001 produces a radial dose profile that is equivalent to that of the detailed simulation within the reached statistical uncertainty of 1%. The effect is also appreciable in the crossline dose profiles estimated for the realistic geometry of the Linac. In another simulation, it was shown that the error made by choosing inappropriate transport parameters can be masked by tuning the energy and focal spot size of the initial beam. Conclusions: The use of large path lengths for the condensed simulation of electrons in a Linac target withpenelope conducts to deviations of the dose in the patient or phantom. Based on the results obtained in this work, values of C 1 and C 2 larger than 0.001 should not be used in Linac targets without further investigation.