Fully-Depleted Silicon-on-Insulator Devices for Radiation Dosimetry in Cancer Therapy

Abstract

The potential of using fully-depleted silicon-on-insulator (FDSOI) devices as dosimeters for radiation cancer therapy is investigated. The response of long-channel FDSOI MOSFETs to radiation from a linear accelerator under various clinical conditions has been measured. Linear response of the device threshold voltage, ${V_{\rm th}}$ , is observed for typical interventional energy X-rays up to absorbed doses as high as 160 Gy. The device response is observed to be strongly influenced by the application of a substrate bias, ${V_{\rm bg}}$ , with sensitivity improvements of up to $20 \times $ observed for ${V_{\rm bg}} =+ 5~\hbox{V}$ compared to ${V_{\rm bg}} = 0$ . The results have been used to calibrate numerical simulations that show the design space for using FDSOI variable capacitors (varactors) as passive wireless radiation dosimeters suitable for in vivo implantation. Simulation studies show that a design space exists to realize wireless sensors with both high quality factor ( $Q > 20$ at 1 GHz) and good sensitivity ( $\Delta f/f = 0.12\% /\hbox{Gy}$ ). These results indicate the promise of FDSOI to realize a new, convenient class of in vivo dosimeters for radiation therapy.