Radiotherapy is a critical component of modern cancer treatment. This complex, multidisciplinary process, however, is susceptible to errors and uncertainties which stem from human error, changes in patient anatomy or treatment delivery. Ensuring the accuracy and safety of radiotherapy delivery is paramount.

This PhD by Prior Publications addresses key challenges in radiotherapy treatment verification, particularly with the adoption of advanced techniques and the novel application of existing systems. The thesis explores two distinct and related themes: local challenges in verification methods and the development of national guidance for online treatment monitoring (OTM).

The first theme demonstrates rigorous verification processes to establish achievable accuracy. This includes investigating the novel application of a Treatment Planning System (TPS) in modelling flattening filter-free (FFF) beams, prior to the widespread commercial implementation of FFF-based treatments. The work also details the independent assessment of a 3D EPID-based dosimetry system, validating its 2D and 3D dose distributions against established detectors and polymer gel dosimetry. These works highlight the need for robust local commissioning and ongoing quality assurance to ensure reproducibility and clinical suitability, especially with the increasing complexity of modern radiotherapy.

The second theme focuses on community engagement and the development of comprehensive guidance for OTM. A UK-wide survey identified barriers to OTM implementation, revealing that despite its recognition as an optimal solution, less than 40% of centres had a clinically active service. This led to the development of a practical guidance document, created in collaboration with the Institute of Physics and Engineering in Medicine (IPEM). This guidance provides a framework for selecting, commissioning, and clinically implementing OTM, including practical methodology for investigating error detection capabilities.

Collectively, this thesis advances the understanding and practice of radiotherapy treatment verification. It provides practical strategies for validating new technologies and fosters community-wide adoption of OTM, ultimately contributing to safer and more effective cancer care.