Pitfalls in the beam modelling process of Monte Carlo calculations for proton pencil beam scanning.

Winterhalter, Carla; Aitkenhead, Adam; Oxley, David; Richardson, Jenny; Weber, Damien C.; MacKay, Ranald I; Lomax, Antony J; Safai, Sairos (2020). Pitfalls in the beam modelling process of Monte Carlo calculations for proton pencil beam scanning. The British journal of radiology, 93(1107), p. 20190919. British Institute of Radiology 10.1259/bjr.20190919

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OBJECTIVE Monte Carlo (MC) simulations substantially improve the accuracy of predicted doses. This study aims to determine and quantify the uncertainties of setting up such a MC system. METHODS Doses simulated with two Geant4-based MC calculation codes, but independently tuned to the same beam data, have been compared. Different methods of MC modelling of a pre-absorber have been employed, either modifying the beam source parameters (descriptive) or adding the pre-absorber as a physical component (physical). RESULTS After the independent beam modelling of both systems in water (resulting in excellent range agreement) range differences of up to 3.6/4.8 mm (1.5% of total range) in bone/brain-like tissues were found, which resulted from the use of different mean water ionisation potentials during the energy tuning process. When repeating using a common definition of water, ranges in bone/brain agreed within 0.1 mm and gamma-analysis (global 1%,1mm) showed excellent agreement (>93%) for all patient fields. However, due to a lack of modelling of proton fluence loss in the descriptive pre-absorber, differences of 7% in absolute dose between the pre-absorber definitions were found. CONCLUSION This study quantifies the influence of using different water ionisation potentials during the MC beam modelling process. Furthermore, when using a descriptive pre-absorber model, additional Faraday cup or ionisation chamber measurements with pre-absorber are necessary. ADVANCES IN KNOWLEDGE This is the first study quantifying the uncertainties caused by the MC beam modelling process for proton pencil beam scanning, and a more detailed beam modelling process for MC simulations is proposed to minimise the influence of critical parameters.

Item Type:

Journal Article (Original Article)

Division/Institute:

04 Faculty of Medicine > Department of Haematology, Oncology, Infectious Diseases, Laboratory Medicine and Hospital Pharmacy (DOLS) > Clinic of Radiation Oncology

UniBE Contributor:

Weber, Damien Charles

Subjects:

600 Technology > 610 Medicine & health

ISSN:

1748-880X

Publisher:

British Institute of Radiology

Language:

English

Submitter:

Beatrice Scheidegger

Date Deposited:

18 Feb 2020 14:48

Last Modified:

23 Feb 2020 01:42

Publisher DOI:

10.1259/bjr.20190919

PubMed ID:

32003576

BORIS DOI:

10.7892/boris.140280

URI:

https://boris.unibe.ch/id/eprint/140280

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