Microdosimetry for hadron therapy: A state of the art of detection technology

Abstract

The interest in hadron therapy is growing fast thanks to the latest technological advances in accelerators and delivery technologies, to the development of more and more efficient and comprehensive treatment planning tools, and due to its increasing clinical adoption proving its efficacy. A precise and reliable beam quality assessment and an accurate and effective inclusion of the biological effectiveness of different radiation qualities are fundamental to exploit at best its advantages with respect to conventional radiotherapy. Currently, in clinical practice, the quality assurance (QA) is carried out by means of conventional dosimetry, while the biological effectiveness of the radiation is taken into account considering the Relative Biological Effectiveness (RBE). The RBE is considered a constant value for protons and it is estimated as a function of the absorbed dose in case of carbon ions. In this framework, microdosimetry could bring a significant improvement to both QA and RBE estimation. By measuring the energy deposited by the radiation into cellular or sub-cellular volumes, microdosimetry could provide a unique characterisation of the beam quality on one hand, and a direct link to radiobiology on the other. Different detectors have been developed for microdosimetry, from the more conventional tissue equivalent proportional counter (TEPC), silicon-based and diamond-based solid-state detectors, to ΔE-E telescope detectors, gas electrons multiplier (GEM), hybrid microdosimeters and a micro-bolometer based on Superconducting QUantum Interference Device (SQUID) technology. However, because of their different advantages and drawbacks, a standard device and an accredited experimental methodology have not been unequivocally identified yet. The establishment of accepted microdosimetry standard protocols and code of practice is needed before the technique could be employed in clinical practice. Hoping to help creating a solid ground on which future research, development and collaborations could be planned and inspired, a comprehensive state of the art of the detector technologies developed for microdosimetry is presented in this review, discussing their use in clinical hadron therapy conditions and considering their advantages and drawbacks.

Space radiation quality factor for Galactic Cosmic Rays and typical space mission scenarios using a microdosimetric approach

“…Various passive and active detectors are available for space missions toward radiation quality (e.g., LET spectra) measurements. Active detectors such as TEPCs, besides providing real-time read-out, are generally considered tissue-equivalent and, therefore, suitable for simulating energy deposition spectra in the human tissue (Parisi et al 2022 ). However, TEPC measurements for simulated tissue volumes at the nanometer scale (diameter < 100 nm) are difficult and less reliable.…”

Investigating different geometrical parameters affecting the electric field of cylindrical microdosimeter

“…As energetic ions interact with matter, they dissipate energy to atoms and molecules in a unique and stochastic manner [2]. Microdosimetry is a radiation science whose aim is to investigate the stochastic nature of the interaction between radiation and the matter and stochastic deposition of ionizing energy by ions moving in the matter in micrometric volumes of the size of similar dimensions to biological cells [3][4][5][6]. Since microdosimetry research provides a better understanding of the fundamental mechanisms of radiation damage in biological effects, experimental microdosimetry has found applications in radiation biology, radiation therapy for cancer treatment, and radiation protection [7].…”

Diamond based integrated detection system for dosimetric and microdosimetric characterization of radiotherapy ion beams

“…To date, the reference microdosimeter is the tissue‐equivalent proportional counter (TEPC), whose SV is filled with low pressure tissue equivalent (TE) gas 9,10 . Microdosimetric measurements with TEPCs were proposed and used to assess the RBE of the radiation though appropriate response functions and models 11–14 . However, there are several issues in using TEPCs in clinical practice, mainly due to the relatively large physical size of the detector, such as the limitation in the sustainable beam particle flux leading to pile‐up effects and the poor capability to perform beams characterizations with high spatial accuracy.…”

“…9,10 Microdosimetric measurements with TEPCs were proposed and used to assess the RBE of the radiation though appropriate response functions and models. [11][12][13][14] However,there are several issues in using TEPCs in clinical practice, mainly due to the relatively large physical size of the detector, such as the limitation in the sustainable beam particle flux leading to pile-up effects and the poor capability to perform beams characterizations with high spatial accuracy.In addition,they operate using high voltages and their use can be impractical in clinical facilities.…”