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要旨:
Deep-seated
tumors can be efficiently treated with heavy charged particles. The characteristic
depth dose profile inside the tissue (Bragg peak) allows to deliver
a high dose inside the tumor, while sparing the neighboring healthy tissue.
As compared to protons, heavy ions like carbon or oxygen produce a higher
amount of ionization events along their track (and in particular at the end
of the ion beam path), resulting in an irreparable damage to the DNA of the
tumor cells. The density of such ionization events is described in terms of
Linear Energy Transfer (LET), an important physical quantity, but difficult
to be measured directly. The aim of this work is to determine LET of hadrontherapy
beams by using Liquid Ionization Chambers (LIC). The ionization
signal in LICs is affected by recombination effects that depend on the LET
of the incident radiation. Differences in recombination effects in LICs and
air-filled ionization chambers can be exploited to obtain the recombination
index, which can be related to the LET, calculated by Monte Carlo methods.
We thus developed a method to construct a calibration curve, which relates
the recombination index with the LET at each depth in water. The result of
this work can be used for online monitoring of the ion beam quality.
