Dependence of LET on material and its impact on current RBE model

• Published in: Physics in medicine & biology Vol. 64; no. 13; p. 135022
• Main Authors: Qi Tan, Hong, Yang Calvin Koh, Wei, Kuan Rui Tan, Lloyd, Hao Phua, Jun, Wei Ang, Khong, Yong Park, Sung, Siang Lew, Wen, Cheow Lei Lee, James
• Format: Journal Article
• Language: English
• Published: England 05-07-2019
• Subjects: Humans; Linear Energy Transfer; Models, Biological; Proton Therapy; Radiometry; Relative Biological Effectiveness; Uncertainty
• ISSN: 1361-6560
• DOI: 10.1088/1361-6560/ab1c90

Biological uncertainty remains one of the main sources of uncertainties in proton therapy, and is encapsulated in a scalar quantity known as relative biological effective (RBE). It is currently recognised that a constant RBE of 1.1 is not consistent with radiobiological experiment and may lead to sub-optimal exploitation of the benefits of proton therapy. To overcome this problem, several RBE models have been developed, and in most of these models, there is a dependence of RBE on dose-averaged linear energy transfer (LET), [Formula: see text]. In this work, we show that the [Formula: see text] estimation in these models during the data-fitting (or parameter estimation) phase could be subjected to a huge uncertainty due to not taking into account cellular materials during simulation, and this uncertainty can propagate down to the resulting RBE models. The dosimetric impact of this [Formula: see text] uncertainty is then evaluated on a simple clinical spread out Bragg peak (SOBP) and a prostate example. Our simulation shows that [Formula: see text] uncertainty due to the use of water as cellular material is non-negligible under low [Formula: see text] and low dose (2 Gy), and can be neglected otherwise. Thus, this study indicates that further dose and range margins may be required for low [Formula: see text] target under low dose. This is due to greater uncertainties in RBE model associated with incomplete knowledge of cellular composition for [Formula: see text] computation.