Abstract
The aim of this work was to model the characteristics of a clinical proton spot scanning beam using Monte Carlo simulations with the code MCNP6. The proton beam was defined using parameters obtained from beam commissioning at the Skandion Clinic, Uppsala, Sweden. Simulations were evaluated against measurements for proton energies between 60 and 226 MeV with regard to range in water, lateral spot sizes in air and absorbed dose depth profiles in water. The model was also used to evaluate the experimental impact of lateral signal losses in an ionization chamber through simulations using different detector radii. Simulated and measured distal ranges agreed within 0.1 mm for R90 and R80, and within 0.2 mm for R50. The average absolute difference of all spot sizes was 0.1 mm. The average agreement of absorbed dose integrals and Bragg-peak heights was 0.9%. Lateral signal losses increased with incident proton energy with a maximum signal loss of 7% for 226 MeV protons. The good agreement between simulations and measurements supports the assumptions and parameters employed in the presented Monte Carlo model. The characteristics of the proton spot scanning beam were accurately reproduced and the model will prove useful in future studies on secondary neutrons.
Highlights
The interaction properties of protons enabling substantial energy depositions in the Bragg peak at welldefined depths have established proton radiation therapy as a suitable option for treating tumors with considerable sparing of the surrounding normal tissues [1,2,3]
Integral depth dose (IDD) curves in water for nominal proton energies between 60 and 226 MeV in steps of 5 MeV were obtained from measurements performed at commissioning using a PTW 34070 Bragg peak plane-parallel ionization chamber (IC) with an active radius of 4.08 cm (PTWFreiburg, Freiburg, Germany)
Integral depth dose in water and lateral beam size in air Ranges derived from simulated and measured IDD agreed within 0.1 mm for R90 and R80, and within 0.2 mm for R50
Summary
The interaction properties of protons enabling substantial energy depositions in the Bragg peak at welldefined depths have established proton radiation therapy as a suitable option for treating tumors with considerable sparing of the surrounding normal tissues [1,2,3]. The properties of proton beams can vary substantially between different proton facilities and should be characterized to allow for an independent validation of the performance of the treatment planning system (TPS). In order to characterize a proton beam a verification of different physical quantities such as depth and lateral dose distribution is essential. This verification can be performed by modelling the proton interactions, the beam transport through the beamline and the patient using Monte Carlo (MC) simulations.
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