3D silicon microdosimetry and RBE study using 12C ion of different energies

L T Tran,M Jackson,D Prokopovich,D Bolst,N Matsufuji,M Lerch,D Hinde,L Chartier,A Stuchbery,V Perevertaylo,M Reinhard,M Petasecca,A B Rosenfeld,M Dasgupta,S Guatelli

doi:10.1088/1742-6596/777/1/012037

Abstract

This paper presents a new version of the 3D mesa “bridge” microdosimeter comprised of an array of 4248 silicon cells fabricated on 10 µm thick silicon-on-insulator substrate. This microdosimeter has been designed to overcome limitations existing in previous generation silicon microdosimeters and it provides well-defined sensitive volumes and high spatial resolution. The charge collection characteristics of the new 3D mesa microdosimeter were investigated using the ANSTO heavy ion microprobe, utilizing 5.5 MeV He2+ ions. Measurement of microdosimetric quantities allowed for the determination of the Relative Biological Effectiveness of 290 MeV/u and 350 MeV/u 12C heavy ion therapy beams at the Heavy Ion Medical Accelerator in Chiba (HIMAC), Japan. The microdosimetric RBE obtained showed good agreement with the tissue-equivalent proportional counter. Utilizing the high spatial resolution of the SOI microdosimeter, the LET spectra for 70 MeV 12C+6 ions, like those present at the distal edge of 290 and 350 MeV/u beams, were obtained as the ions passed through thin layers of polyethylene film. This microdosimeter can provide useful information about the lineal energy transfer (LET) spectra downstream of the protective layers used for shielding of electronic devices for single event upset prediction.

Highlights

Heavy ions deposit energy in matter much differently to X-rays, depositing most of their energy near the end of their range, commonly known as the Bragg peak (BP)
For measurements with 70 MeV carbon ions the microdosimeter was able to measure at the end of the carbon BP with 10 μm depth increments while mesurements were done with 0.5 mm depth increments for the 290 MeV/u beam. These results have demonstrated the BridgeV2 microdosimeters extremely high spatial resolution and ability to detect pecularities in ion lineal energy transfer (LET) within extremely thin layers of shielding material, relevant for space application and shielding verification
The new Centre for Medical Radiation Physics (CMRP) 3D bridge microdosimeter was investigated in detail using scanning electron microscopy and 5.5 MeV He2+ microbeams

Summary

Introduction

Heavy ions deposit energy in matter much differently to X-rays, depositing most of their energy near the end of their range, commonly known as the Bragg peak (BP). This characteristic is advantageous for radiotherapy as the highest dose can be delivered to the target volume with much lower doses to the surrounding healthy tissue. Published under licence by IOP Publishing Ltd or in cancer therapy, it is important to understand how the ion LET varies with depth, in addition to its relative biological effectiveness (RBE)

Methods

Results

Conclusion