Unflattened Radiotherapy beams; characterisation, optimisation and application

The goal of this thesis was to investigate flattening filter free (FFF) beams produced by medical linear accelerators for radiotherapy applications, from their initial setup through to their clinical implementation. This was split into four sections that comprise the main experimental chapters of this thesis. The characteristics of FFF beams both matched (by tuning beam quality to the equivalent cFF beam) and unmatched were compared to conventional flattening filter (cFF) beams. The characterisation of FFF beams highlighted inconsistencies with the current parameters used for the description and quality assurance (QA) of cFF beams. New methods suitable for the QA of both cFF and FFF beams were investigated and proposed. The use of Monte Carlo (MC) modelling was investigated to determine how to model an FFF beam and facilitate further investigations. Treatment planning studies were performed for lung stereotactic ablative radiotherapy (SABR), pelvic SABR and Head and Neck volumetric modulated arc therapy (VMAT). The planning work concluded that clinically acceptable plans were achievable through the use of FFF beams and provides a solid basis for clinical implementation. The work overall provides a comprehensive set of practical data and methods to support the use of FFF beams in clinical practice.