Micro-and nanodosimetry for radiobiological planning in radiotherapy and cancer risk assessment in radiation environment

Full text: Microdosimetry and nanodosimetry can provide unique information for prediction of radiobiological properties of radiation, which is important in radiation therapy for accurate dose planning and in radiation protection for cancer induction risk assessment. This demand measurements of the pattern of energies deposited by ionizing radiation on cellular scale and DNA levels.Silicon microelectronics technology is offering a unique opportunity for replacing gas proportional counters (TEPC) with miniature detectors for regional microdosimetry. Silicon on Insulator (SOI) technology has been used for the development of arrays of micron size sensitive volumes for modelling energy deposited in biological cells. The challenge in silicon microdosimetry is the development of well defined sensitive volume (SV) and full charge collection deposited by ionizing radiation in the SV. First generation SOI microdosimeters were developed at CMRP and investigated in a wide range of radiation fields for proton and neutron therapies and recently on isotopic neutron sources and heavy ions with energy up to lGeV/jj,m which are typical for deep space radiation environment. Microdosimetric spectra were obtained in a phantom that are well matched to TEPC and Monte Carlo simulations. Evidence that radiations with the same LET exhibit different biological effects demand development of new sensors sensitive to the track structure of ions or the type of particle for prediction of radiobiological effect of radiation using radiobiological models. New monolithic Si AE-E telescope of cellular size for simultaneous regional microdosimetry and particle identification will be presented and results will be discussed. The new design of the SOI microdosimeter is based on 3D micron and submicron size of Si SVs. This approach allows improvement in the accuracy of the Si microdosimetry because of full charge collection and the ability to measure low LET as low as 0.01 keV/jjm, which is similar to TEPC. Microdosimetric and nanodosimetric measurements of 250 MeV proton radiation fields at the proton accelerator of Loma Linda University Medical Center (LLUMC) using SOI microdosimeter and gas nanodosimeter will be presented. Good agreement between GEANT Monte Carlo simulations of ionization cluster and pattern of deposited energies measured by nanodosimeter and microdosimeter have been achieved. Replacement of a gas nanodosimeter with 10 nm SV volume of a silicon detector is a challenge. However with the development of Si nanotechnology it is feasible and track structure sensitive array of 3D submicron size Si detectors will be presented. Challenges in the conversion of Si microdosimetric and nanodosimetric spectra to tissue equivalent will be discussed. This project is a large scale collaboration with ANSTO and U NSW in Australia and LLUMC, USNA, Johns Hopkins Uni and MSKCC in the USA