Experimental assessment of proton dose calculation accuracy in inhomogeneous media

J Sorriaux; M Testa; H Paganetti; J Orban de Xivry; J A Lee; E Traneus; K Souris; S Vynckier; E Sterpin

doi:10.1016/j.ejmp.2017.04.020

Experimental assessment of proton dose calculation accuracy in inhomogeneous media

Phys Med. 2017 Jun:38:10-15. doi: 10.1016/j.ejmp.2017.04.020. Epub 2017 May 8.

Authors

J Sorriaux¹, M Testa², H Paganetti³, J Orban de Xivry⁴, J A Lee⁵, E Traneus⁶, K Souris⁵, S Vynckier⁷, E Sterpin⁸

Affiliations

¹ Université catholique de Louvain, Molecular Imaging Radiotherapy & Oncology, Brussels, Belgium; Université catholique de Louvain, ICTEAM Institute, Louvain-la-Neuve, Belgium. Electronic address: jefferson.sorriaux@gmail.com.
² Yonsei University, Department of Radiation Convergence Engineering, Wonju, South Korea.
³ Massachusetts General Hospital and Harvard Medical School, Department of Radiation Oncology, Boston, MA 02114, USA.
⁴ Ion Beam Applications s.a, Louvain-la-Neuve, Belgium.
⁵ Université catholique de Louvain, Molecular Imaging Radiotherapy & Oncology, Brussels, Belgium; Université catholique de Louvain, ICTEAM Institute, Louvain-la-Neuve, Belgium.
⁶ Raysearch Laboratories AB, Stockholm, Sweden.
⁷ Cliniques Universitaires Saint-Luc, Brussels, Belgium.
⁸ Université catholique de Louvain, Molecular Imaging Radiotherapy & Oncology, Brussels, Belgium; KU Leuven, Department of Oncology, Laboratory of Experimental Radiotherapy, Leuven, Belgium.

PMID: 28610689
DOI: 10.1016/j.ejmp.2017.04.020

Abstract

Purpose: Proton therapy with Pencil Beam Scanning (PBS) has the potential to improve radiotherapy treatments. Unfortunately, its promises are jeopardized by the sensitivity of the dose distributions to uncertainties, including dose calculation accuracy in inhomogeneous media. Monte Carlo dose engines (MC) are expected to handle heterogeneities better than analytical algorithms like the pencil-beam convolution algorithm (PBA). In this study, an experimental phantom has been devised to maximize the effect of heterogeneities and to quantify the capability of several dose engines (MC and PBA) to handle these.

Methods: An inhomogeneous phantom made of water surrounding a long insert of bone tissue substitute (1×10×10 cm³) was irradiated with a mono-energetic PBS field (10×10 cm²). A 2D ion chamber array (MatriXX, IBA Dosimetry GmbH) lied right behind the bone. The beam energy was such that the expected range of the protons exceeded the detector position in water and did not attain it in bone. The measurement was compared to the following engines: Geant4.9.5, PENH, MCsquare, as well as the MC and PBA algorithms of RayStation (RaySearch Laboratories AB).

Results: For a γ-index criteria of 2%/2mm, the passing rates are 93.8% for Geant4.9.5, 97.4% for PENH, 93.4% for MCsquare, 95.9% for RayStation MC, and 44.7% for PBA. The differences in γ-index passing rates between MC and RayStation PBA calculations can exceed 50%.

Conclusion: The performance of dose calculation algorithms in highly inhomogeneous media was evaluated in a dedicated experiment. MC dose engines performed overall satisfactorily while large deviations were observed with PBA as expected.

Keywords: Inhomogeneous phantom; Monte carlo; Pencil beam scanning; Proton therapy; Quality assurance.

MeSH terms

Algorithms*
Humans
Monte Carlo Method
Phantoms, Imaging*
Protons
Radiometry
Radiotherapy Dosage*
Radiotherapy Planning, Computer-Assisted*

Substances

Protons