Radiotherapy Dose Verification with Cherenkov Light

Modern radiotherapy delivers treatment with a 360 rotating gantry that produces X-rays in a continuous arc around the patient. This X-ray beam is continuously modulated and shaped by adjusting both its intensity and the shape of the beam. This results in a highly conformal dose distribution that changes continuously over time, making dosimetry during treatment significantly more complex than when treatment is delivered with static fields. There is currently no widely accepted method for 4D in-vivo dosimetry in the clinical setting, and we believe that imaging the Cherenkov light emission of excited electrons could fill that gap. As the X-rays deposit dose, energetic electrons moving faster than the speed of light in tissue are produced: the subsequent emission of Cherenkov light can be recorded to reconstruct the 4D dose distribution. Cherenkov imaging therefore allows the radiation field to be imaged in real time and connected to anatomical landmarks (registration). This will give greater confidence that the planned dose is actually being delivered, enabling real-time detection - and ultimately correction - of discrepancies between the planned and delivered dose, giving clinicians the confidence to trial more advanced therapies. Experiments at UCL have demonstrated that the radiotherapy treatment beam from a radiotherapy gantry generates visible Cherenkov light which can be imaged with a standard consumer digital SLR camera. Other groups have generated in vivo movies showing the Cherenkov light emitted as treatment progresses. This project will build on this previous work and demonstrate the application of Cherenkov imaging for real-time in-vivo verification. The techniques that are developed in this project are medical image reconstruction, Geant4-based Monte Carlo simulations which are used to simulate the Cherenkov emissions, and the application of deep-learning techniques to optimise the reconstruction of the Cherenkov emissions.