The advancements in modern radiotherapy techniques have increased the demand for precise and reliable dosimeters capable of operating in small field and ultra-high dose rate environments. This research focuses on developing a single crystal chemical vapour deposition diamond dosimeter to address limitations in conventional dosimetry systems and improve accuracy in advanced radiotherapy applications.

Monte Carlo simulations and experimental evaluations, conducted in collaboration with the National Physical Laboratory, guided the optimisation of a sandwich-type diamond dosimeter prototype. Design refinements targeted to improve stability and signal-to-noise ratio, reduce leakage current, and enhance dosimetric measurement feasibility and dose distribution accuracy across the radiation field. By addressing perturbations arising from detector components, encapsulation materials, and the electrode/diamond interface, these efforts led to three generations of prototypes manufactured by Micron Semiconductor Ltd.

The final encapsulated prototype, the Micron DD, with a sensitive volume of ∼0.3 mm³, underwent comprehensive dosimetric characterisation in high-energy X-ray beams across conventional and high dose rates, including small fields. The detector demonstrated strong spatial resolution for dose profile and depth dose acquisition, dose linearity, short-term repeatability, and stability, with performance comparable to commercially established dosimeters. A small field output correction factor was required only for the 1 × 1 cm² field, agreeing within 1.6% with that of the PTW 60019 microDiamond. Experimental and Monte Carlo results of the above dosimetric properties were consistent across all field sizes investigated.

However, low charge collection efficiency, dose rate and energy dependence, and angular response variability indicated the need for further optimisation, particularly in electrode/diamond interface quality and detector design. A proposed Monte Carlo-modelled design, incorporating reduced printed circuit board plating and improved symmetry, demonstrated reduced perturbations and enhanced performance.

This research demonstrates the feasibility of a high-performance diamond dosimeter for small field radiotherapy and lays the groundwork for future investigations in proton therapy and ultra-high dose rate applications.