TY - JOUR
T1 - Experimentally validated pencil beam scanning source model in TOPAS
AU - Lin, Liyong
AU - Kang, Minglei
AU - Solberg, Timothy D.
AU - Ainsley, Christopher G.
AU - McDonough, James E.
N1 - Publisher Copyright:
© 2014 Institute of Physics and Engineering in Medicine.
PY - 2014/11/21
Y1 - 2014/11/21
N2 - The presence of a low-dose envelope, or 'halo', in the fluence profile of a proton spot can increase the output of a pencil beam scanning field by over 10%. This study evaluated whether the Monte Carlo simulation code, TOPAS 1.0-beta 8, based on Geant4.9.6 with its default physics list, can predict the spot halo at depth in phantom by incorporating a halo model within the proton source distribution. Proton sources were modelled using three 2D Gaussian functions, and optimized until simulated spot profiles matched measurements at the phantom surface out to a radius of 100 mm. Simulations were subsequently compared with profiles measured using EBT3 film in Solidwater® phantoms at various depths for 100, 115, 150, 180, 210 and 225 MeV proton beams. Simulations predict measured profiles within a 1 mm distance to agreement for 2D profiles extending to the 0.1% isodose, and within 1 mm/1% Gamma criteria over the integrated curve of spot profile as a function of radius. For isodose lines beyond 0.1% of the central spot dose, the simulated primary spot sigma is smaller than the measurement by up to 15%, and can differ by over 1 mm. The choice of particle interaction algorithm and phantom material were found to cause ∼1 mm range uncertainty, a maximal 5% (0.3 mm) difference in spot sigma, and maximal 1 mm and ∼2 mm distance to agreement in isodoses above and below the 0.1% level, respectively. Based on these observations, therefore, the selection of physics model and the application of Solidwater® as water replacement material in simulation and measurement should be used with caution.
AB - The presence of a low-dose envelope, or 'halo', in the fluence profile of a proton spot can increase the output of a pencil beam scanning field by over 10%. This study evaluated whether the Monte Carlo simulation code, TOPAS 1.0-beta 8, based on Geant4.9.6 with its default physics list, can predict the spot halo at depth in phantom by incorporating a halo model within the proton source distribution. Proton sources were modelled using three 2D Gaussian functions, and optimized until simulated spot profiles matched measurements at the phantom surface out to a radius of 100 mm. Simulations were subsequently compared with profiles measured using EBT3 film in Solidwater® phantoms at various depths for 100, 115, 150, 180, 210 and 225 MeV proton beams. Simulations predict measured profiles within a 1 mm distance to agreement for 2D profiles extending to the 0.1% isodose, and within 1 mm/1% Gamma criteria over the integrated curve of spot profile as a function of radius. For isodose lines beyond 0.1% of the central spot dose, the simulated primary spot sigma is smaller than the measurement by up to 15%, and can differ by over 1 mm. The choice of particle interaction algorithm and phantom material were found to cause ∼1 mm range uncertainty, a maximal 5% (0.3 mm) difference in spot sigma, and maximal 1 mm and ∼2 mm distance to agreement in isodoses above and below the 0.1% level, respectively. Based on these observations, therefore, the selection of physics model and the application of Solidwater® as water replacement material in simulation and measurement should be used with caution.
KW - Monte Carlo simulation
KW - Solidwater®
KW - pencil beam scanning
KW - proton therapy
KW - treatment planning
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U2 - 10.1088/0031-9155/59/22/6859
DO - 10.1088/0031-9155/59/22/6859
M3 - Article
C2 - 25349982
AN - SCOPUS:84908568354
SN - 0031-9155
VL - 59
SP - 6859
EP - 6873
JO - Physics in medicine and biology
JF - Physics in medicine and biology
IS - 22
ER -