Characterization of an innovative p-type epitaxial diode for dosimetry in modern external beam radiotherapy

Due to the ever-increasing complexity of treatment modalities in radiation therapy, there has been a greater need for detectors to perform quality assurance to ensure patients are treated correctly and safely. Modern radiation therapy techniques involve small field sizes, high dose gradients, and varying intensity of energy and rate. The ideal dosimeter for this treatment should display high spatial resolution, high linearity, accuracy, and radiation hardness. Silicon detectors have been widely used for radiotherapy measurements and have many attractive qualities as a dosimeter; weaknesses of silicon detectors are, however, decreases in sensitivity with accumulated dose. The Centre for Medical Radiation Physics has developed a new technology with an unusual charge collection efficiency variation with accumulated dose which stabilizes the response of the detector within 5% after 120 kGy photon irradiation. The sensor has been also characterized by irradiation by an 18 MV medical LINAC with sensitivity to a photoneutron-induced damage of less than 0.5%/100 Gy. The radiation damage mechanism has been validated by TCAD simulations which confirmed the mechanism behind the CCE increase as a function of the accumulated dose.