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Cancers 2015, 7(1), 460-480; doi:10.3390/cancers7010460

Towards Achieving the Full Clinical Potential of Proton Therapy by Inclusion of LET and RBE Models

Gray Laboratory, CRUK/MRC Oxford Oncology Institute, The University of Oxford, ORCRB-Roosevelt Drive, Oxford OX3 7DQ, UK
Academic Editor: Xiaodong Zhang
Received: 2 December 2014 / Revised: 19 January 2015 / Accepted: 6 March 2015 / Published: 17 March 2015
(This article belongs to the Special Issue Proton Therapy for Cancer)
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Abstract

Despite increasing use of proton therapy (PBT), several systematic literature reviews show limited gains in clinical outcomes, with publications mostly devoted to recent technical developments. The lack of randomised control studies has also hampered progress in the acceptance of PBT by many oncologists and policy makers. There remain two important uncertainties associated with PBT, namely: (1) accuracy and reproducibility of Bragg peak position (BPP); and (2) imprecise knowledge of the relative biological effect (RBE) for different tissues and tumours, and at different doses. Incorrect BPP will change dose, linear energy transfer (LET) and RBE, with risks of reduced tumour control and enhanced toxicity. These interrelationships are discussed qualitatively with respect to the ICRU target volume definitions. The internationally accepted proton RBE of 1.1 was based on assays and dose ranges unlikely to reveal the complete range of RBE in the human body. RBE values are not known for human (or animal) brain, spine, kidney, liver, intestine, etc. A simple efficiency model for estimating proton RBE values is described, based on data of Belli et al. and other authors, which allows linear increases in α and β with LET, with a gradient estimated using a saturation model from the low LET α and β radiosensitivity parameter input values, and decreasing RBE with increasing dose. To improve outcomes, 3-D dose-LET-RBE and bio-effectiveness maps are required. Validation experiments are indicated in relevant tissues. Randomised clinical studies that test the invariant 1.1 RBE allocation against higher values in late reacting tissues, and lower tumour RBE values in the case of radiosensitive tumours, are also indicated. View Full-Text
Keywords: proton therapy; radiotherapy; RBE; mathematical model; radiobiology proton therapy; radiotherapy; RBE; mathematical model; radiobiology
This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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Jones, B. Towards Achieving the Full Clinical Potential of Proton Therapy by Inclusion of LET and RBE Models. Cancers 2015, 7, 460-480.

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