3D-mesa 'bridge' silicon microdosimeter: charge collection study and application to RBE studies in 12C radiation therapy

Microdosimetry is an extremely useful technique, used for dosimetry in unknown mixed radiation fields typical of space and aviation, as well as in hadron therapy. A new silicon microdosimeter with 3D sensitive volumes has been proposed to overcome the shortcomings of the conventional Tissue Equivalent Proportional Counter. In this article, the charge collection characteristics of a new 3D mesa microdosimeter were investigated using the ANSTO heavy ion microprobe utilizing 5.5 MeV rm He2 + and 2 MeV rm H + ions. Measurement of the microdosimetric characteristics allowed for the determination of the Relative Biological Effectiveness of the 12rm C heavy ion therapy beam at the Heavy Ion Medical Accelerator in Chiba (HIMAC), Japan. Well-defined sensitive volumes of the 3D mesa microdosimeter have been observed and the microdosimetric RBE obtained showed good agreement with the TEPC. The new 3D mesa 'bridge' microdosimeter is a step forward towards a microdosimeter with fully free-standing 3D sensitive volumes.