Session Item

In microdosimetry (microdosimetric kinetic model) precise measurements of the lineal energy of particles are used to model the relative biological effectiveness (RBE) of clinical beams. The aim of this work was to measure the microdosimetric distributions of different ion beams, namely proton, carbon and silicon, using a novel diamond-based microdosimeter with well-defined micro-sensitive volumes (µSV). 

DIAµDOS Guard-Ring microdosimeter is an scCVD (single crystal chemical vapor deposition) diamond-membrane-based microdosimeter with cylindrical-shaped µSVs of 60 μm diameter and 12 μm thickness. During the irradiation with particle beams, the diamond microdosimeters were connected to low noise electronics allowing the detection of lineal energies of less than 10 keV/µm. The diamond microdosimeters provide very high spatial resolution and are more tissue-equivalent when compared with other existing alternative technologies. The response of DIAµDOS Guard-Ring microdosimeters was studied in 290 MeV/u carbon and 230 MeV/u silicon passive ion beams, and 200 MeV proton and 290 MeV/u carbon scanning therapy beams at heavy-ion medical accelerator in Chiba (HIMAC) in Japan, Institute Curie Proton Therapy Center in Orsay (CPO) in France and Gunma University Heavy Ion Medical Center (GHMC) in Japan, respectively. The diamond microdosimeters were positioned at various depths in a water phantom or behind a solid-water wall along the central axis of the ion beam. The microdosimetric lineal energy spectra were measured for pristine Bragg peak (BP). Geant4 simulations were performed in order to compare the simulated spectra to the experimental results.

Figure 1 (A) shows the measured energy spectra of a passive 290 MeV/u carbon ion beam at HIMAC in Japan. The insert in the right corner represents the measured absorbed dose for this ion beam. Characteristic spectra for the corresponding positions in the Bragg peak can be observed. In Figure 1 (B) and (C) the microdosimetric spectra of the carbon beam are shown. A general trend can be observed in which there is an increase in lineal energy at Bragg peak and its distal part. These characteristics have been observed for all measured ion types and energies. 

The diamond DIAµDOS Guard-Ring microdosimeter with its well-defined micro-sensitive-volumes has shown its ability in characterization of particle radiation fields and can measure relevant physical parameters for the later determination of the RBE. Good agreement was observed between the experimental and simulation results, confirming the potential application of this microdosimeter in particle therapy.