Monitoring late radiation damage in normal muscle tissue with electrical impedance spectroscopy

During radiation treatment for cancer, normal tissue will be exposed to radiation and it is the response of this tissue and the risk of complications that limits the prescribed dose and the efficacy of treatment. The response to radiation exposure is dose, time and tissue-type dependent and has been studied extensively in animal and human systems. However, there remains significant heterogeneity among individuals. Systematic and quantitative monitoring of tissue response with electrical impedance spectroscopy (EIS) might providing insight into early warning signs of late effects which could be used to alter the course of therapy on an individual patient basis. The implementation of EIS in three clinically relevant radiation settings is described. A kilovolt unit (orthovoltage, x-ray), a linear accelerator (x-ray), and an implantable radionuclide source (high dose rate, iridium-192 seed) were employed for the irradiation of muscle in the hind leg of rats. Doses of 70 Gy, 90 Gy, and 150 Gy were delivered with orthovoltage, nominal doses of 70 and 90 Gy which translate to doses of approximately 50 and 63 Gy at a 5mm distance from the center were employed with the linear accelerator, and doses of 26 and 52 Gy, at 5mm, were employed with the HDR system. The responses were monitored from 1–4 months post-irradiation. In all cases, EIS was capable of detecting a dose and time response, suggesting that EIS may indeed have a role to play in three of the most common irradiation procedures.