On the Possibility to Use the Charge Imbalance in Patients Undergoing Radiotherapy: A New Online, In Vivo, Noninvasive Dose Monitoring System

This paper describes a new real-time, in vivo, noninvasive, biasless detector system acting as a beam monitoring and relative dose measurement system. The detector is based on the idea that when a beam current is injected into the body of a patient undergoing a charged particle therapy, the current itself can be collected using a conductive electrode in contact with the patient’s skin. This new approach was studied in vitro using an electrically isolated water tank irradiated with monoenergetic proton beams. The conductive electrode was immersed in water and positioned outside the irradiation field. The detection system performance was evaluated by comparing its response against a SEM (Secondary Emission Monitor) detector, used as a reference beam current monitor, and an Advanced Markus ionization chamber. Short-, mid- and long-term reproducibility, current monitoring capability, field size dependence, electrode position and environment temperature dependence, linearity with dose, and dose rate dependence were investigated. Few preliminary in vivo tests were also performed that demonstrated the possibility to apply the system in clinical practice. The potential of the proposed method is considerable, representing a simple and economical system for online, in vivo, and noninvasive monitoring of the beam current and relative released dose into the patient during treatment, without perturbing the irradiation field. The system presented in this work is protected with both a National Italian (N. 102017000087851) and an International N. WO 2019/025933 patent