OPTIma: Optimising Proton Therapy through Imaging

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Over 350,000 cancer cases are diagnosed annually in the UK with some 40% of patients receiving radiotherapy as part of their curative treatment. Most radiotherapy treatments employ external x-ray beams generated by linacs. However, there is a growing interest in the use of high-energy proton beams for radiotherapy. Within the UK, two NHS centres and several private ones will open in the next few years. Proton Beam Therapy is most useful for tumours in the head/neck region, some brain tumours, tumours near to organs at risk and childhood cancers. Protons lose their energy in a very different way to x-rays (photons) as they have a finite range in tissue with most of their energy being deposited near the end of this range. So protons can target a tumour with a focused dose with less exposure of healthy tissue to radiation. The challenge is, clearly, predicting accurately where the protons will deposit the bulk of their energy - in the target tumour and not in neighbouring healthy tissue. Treatment planning is currently based on x-ray CT imagery but this gives rise to unavoidable uncertainties in translating from images based on low energy x-rays to the ranges of high energy protons. The answer is to use the same radiation type to treat and to image - the concept of the 'same ruler'. Imaging with protons has proved difficult as it is necessary to track individuals protons as they pass through a patient or phantom and record the corresponding residual energy of each proton. Our previous project, PRaVDA, laid the foundations of this for a broad beam of protons. Current Proton Beam Therapy facilities use small diameter beams that are electromagnetically scanned over the target region. This implies a radically different instrument concept and design, but based on our experience with PRaVDA. The philosophy is to provide a robust, turn-key (as far as feasible for a cutting-edge instrument) that can be exploited by a wider community.This project will provide a national facility in the unique Research Room at The Christie Proton Beam Therapy Centre, Manchester, for exploring proton imaging with a state-of-the-art scanning pencil-beam delivery system. This will open up to the research community a new medical imaging modality - charged-particle imaging in radiotherapy. The main project aims are:Explore the capabilities of proton CT and radiography in reducing range uncertainties to a level that do not influence optimum treatment planning.Develop algorithms for complex biological samples that provide in a computationally efficient manner satisfactory and quantifiable imagery.Combining different modes of proton CT and other imagery (x-ray CT, PET, etc) to provide more clinical information and improved imagery.Providing a facility and a methodology for the accurate calibration of phantoms for other proton therapy centres.Understanding how proton CT can be successfully integrated in treatment workflows from planning to in and between treatment monitoring. Further the development of proton imaging for gantry systems and encourage commercial exploitation.