Fullarton, Ryan; (2025) Improving the accuracy of Particle Therapy in lung cancer through the development of integrated-mode particle imaging technology. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Particle therapy uses the localised dose deposition of particle beams to accurately treat cancers. However, as a consequence, particle therapy dose distributions are very susceptible to degradation from intrafraction organ motion particularly in the treatment of lung cancer. This work proposes that particle imaging, a technique that uses the transmission of particle beams to form radiological images, could be used to reduce this impact. An investigation of techniques in particle imaging was conducted, starting with the image quality achievable with state-of the art particle image processing. Fol lowing this, a particle imaging detector was designed, constructed and assessed for image quality using both proton beams and carbon ions. The same detector system was used to demonstrate lung tumour tracking using an anthropomorphic phantom simulating breathing motion. Through the development of sophisticated filtering methods for single-event particle imaging, high quality images can be produced with imaging doses as low as 1 µ Gy. Due to the need for faster acquisition, an integrated-mode particle imaging detector was designed and evaluated with two different reconstruction methods. A reconstruction method based on the back-projection of water-equivalent thickness (WET) showed the best image quality. Pencil beam depth measurements showed accuracy within a mean absolute error of < 1.0 mm. Carbon ions were found to produce higher image quality in terms of spatial resolution and contrast with similar accuracy of WET. Finally, it was demonstrated that the positions of objects can be tracked, using the system, to within 2 mm, under conditions where the motion was slowed due to a limitation in acquisition speed. This thesis demonstrated the potential for integrated-mode particle imaging to be used to track lung tumours, leading to more accurate particle therapy treatments. However, it is also shown that there are technological improvements required to achieve clinical translation, including faster beam delivery.

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