TITLE:
LET Monitoring Using Liquid Ionization Chambers
AUTHORS:
Sara Tegami, Stephen D. Bello, Shuang Luan, Andrea Mairani, Katia Parodi, Michael H. Holzscheiter
KEYWORDS:
Linear Energy Transfer, Relative Biological Effectiveness, Liquid Ionization Chambers
JOURNAL NAME:
International Journal of Medical Physics, Clinical Engineering and Radiation Oncology,
Vol.6 No.2,
May
26,
2017
ABSTRACT: Relative
biological effectiveness (RBE) is an important quantity in planning particle
beam cancer therapy. In general, the RBE describes the biological effectiveness
of a given primary beam with respect to a reference photon irradiation. RBE
varies not only for different primary beams but also with depth in the target
for a given beam modality. It is not a quantity that easily lends itself to
measurements or computation as it depends on many biological and physical
quantities. Numerous experiments in vitro using various cell
lines and irradiation modalities have shown that a general relationship between
RBE and the physical quantity Linear Energy Transfer (LET) exists. Several
groups have proposed including LET in the radiation therapy treatment planning
instead of the more complicated and elusive RBE. It has been shown that LET is an
important quantity to consider in treating radio-resistant tumors. The concept
of LET painting has been proposed with the goal of improving tumor control
probability (TCP) for hypoxic tumors by focusing high LET radiation on the
hypoxic region of the tumor while restricting the surrounding normal tissue to
low LET radiation. In order to properly incorporate LET in clinical treatment,
it is important to be able to experimentally measure and verify LET
distribution. We propose a novel method for measuring LET using a dual chamber
methodology exploiting the difference in the observed recombination between air
filled ionization chambers (IC) and liquid filled ionization chambers (LIC).
The resulting difference in the measured signals will be used to directly extract
the relative LET of an actual treatment beam in real time. This paper describes
our initial studies of this method, presents preliminary results, and discusses
further improvements toward a practical real-time LET measuring device.