Abstract
The tissue equivalent proportional counter (TEPC) is the most accurate device for measuring the microdosimetric properties of a particle beam, showing to assess the relative biological effectiveness by linking the physical parameters of the radiation field with the corresponding biological response. Nevertheless, no detailed information on the track structure of the impinging particles can be obtained, since the lower operation limit of the common TEPCs is about 0.3 μm. On the other hand, the pattern of particle interactions at the nanometer level, which demonstrated to have a strong correlation with radiation-induced damages to the DNA, is measured directly by only three different nanodosimeters worldwide: practical instruments are not yet available. The gap between microdosimetry and track-nanodosimetry can be filled partially by extending the TEPC response down to the nanometric region. A feasibility study of a novel TEPC designed to simulate tissue-equivalent sites in the nanometric domain was performed. The present paper aims at describing the design, the development and the characterization of this avalanche-confinement TEPC. Irradiations with photons, fast neutrons and low-energy carbon ions demonstrated the capability of this TEPC of measuring in the range 0.3 μm–25 nm.
Highlights
In the last three decades a great interest has grown for hadron therapy, which consists in a radiation therapy modality based on charged particles for treating radio-resistant cancers and malignant tumors close to critical organs[1]
The assessment of the biological effective dose of clinical hadron beams is based on the measurements of the absorbed dose, which is a macroscopic quantity that demonstrated to be not adequate to describe the energy deposition process at micrometric level, because it does not take into account neither the stochastic of particle interaction in the target volume nor the track structure of ionizing charged particles, which is fundamental for initiating of the radiation damage[3]
A more comprehensive physical knowledge of the local energy deposition can be accomplished with high accuracy by innovative methodologies and instruments provided by microdosimetry, which aims at characterizing the statistical fluctuations of the local energy imparted at the micrometric level, and track-nanodosimetry, devoted to the description of the pattern of particle interactions at the nanometric level
Summary
In the last three decades a great interest has grown for hadron therapy, which consists in a radiation therapy modality based on charged particles (protons and other ions such as carbon ions) for treating radio-resistant cancers and malignant tumors close to critical organs[1]. The assessment of the biological effective dose of clinical hadron beams is based on the measurements of the absorbed dose, which is a macroscopic quantity that demonstrated to be not adequate to describe the energy deposition process at micrometric level, because it does not take into account neither the stochastic of particle interaction in the target volume nor the track structure of ionizing charged particles, which is fundamental for initiating of the radiation damage[3]. In order to fill the gap between standard TEPCs and nanodosimeters, an avalanche-confinement TEPC capable of simulating biological sites down to the nanometric region was designed and constructed. This detector was calibrated with an internal alpha source. Its response to fast neutrons and to low-energy carbon ions was assessed experimentally
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