Quality Assurance Dosimetry in Particle Therapy

This thesis presents research pertaining to the application of silicon microdosimetry for radiation protection and quality assurance (QA) in heavy ion therapy. Heavy ion therapy has a number of advantages compared to conventional photon therapy, particularly for treating tumours near high risk organs, due to its greater conformal energy deposition. However, successful treatment with heavy ions depends largely on knowledge of the relative biological effectiveness (RBE) of the radiation produced by primary and secondary charged particles. Sparsely ionising radiation such as x-rays, electrons and gamma rays produce approximately equivalent biological effects for the same absorbed dose. However, heavy ions produce different biological effects for the same absorbed dose. This variation in biological effect is quantified using the relative biological effectiveness (RBE). Regional microdosimetry considers the process of stochastic energy deposition in a region comparable in size to a human cell, allowing for the determination of RBE based on deposited energy by mixed radiation fields. The tissue equivalent proportional counter (TEPC) or miniaturised version (mini-TEPC) remains the gold standard for microdosimetry, however silicon microdosimetry has recently become a viable replacement. This thesis presents continuing development and application of the Mushroom silicon-on-insulator (SOI) 3D microdosimeters developed by the Centre for Medical Radiation Physics (CMRP) at the University of Wollongong (UOW).