Development of Motion Management Techniques for Lung Stereotactic Ablative Radiotherapy Treatment on TomoTherapy

<p dir="ltr">Stereotactic ablative radiotherapy (SABR) delivers high, conformal doses of radiation in 1-5 fractions with submillimetre accuracy, sparing healthy tissues. It is now recognised as the standard of care for early-stage non-small cell lung cancer and recurrent pulmonary lesions, and is expanding to liver, prostate, spine, and other sites.</p><p dir="ltr">TomoTherapy (Accuray, Sunnyvale, CA, USA) combines continuous gantry rotation with a translating couch to produce helical IMRT arcs. A 6 MV fan beam (1-5 cm longitudinal, 40 cm lateral) is modulated by a binary 64-leaf MLC, while the same accelerator produces low-dose MVCT for image guidance. Additionally, TomoTherapy is capable of treating targets up to 160 cm without field junctions. Its demonstrated sub-millimetre delivery accuracy makes it particularly well-suited for lung SABR.</p><p dir="ltr">Respiratory motion remains a significant challenge for lung SABR. AAPM TG-76 classifies five motion-management strategies, namely motion-encompassing, gating, breath-hold, shallow breathing, and respiration-synchronized delivery. Among these five techniques, the candidate has identified two methods, namely motion encompassing and shallow breathing, as potentially implementable motion management techniques for lung SABR treatment on TomoTherapy. Evolving around this topic, the thesis first investigates whether the image quality of MVCT on TomoTherapy is sufficient to support accurate dose calculation. It then examines the potential of robust optimization, an advanced optimization approach that accounts for respiratory motion, to enhance dosimetric outcomes and deliver clinical benefits in lung SABR. Next, following the demonstration of the positive effects of shallow breathing on target coverage, normal tissue sparing, and delivery accuracy, the thesis validates the clinical use of a novel audiovisual biofeedback system to assist with the clinical implementation of shallow breathing on TomoTherapy. Finally, the thesis assesses an individualised quality assurance method for detecting acquisition errors in 4DCT, an essential imaging modality in lung SABR, and quantifies their dosimetric impact.</p><p dir="ltr">Employing a thesis-by-compilation format, the findings of this thesis are presented through five peer- reviewed publications Collectively, these papers demonstrate (1) the feasibility of using MVCT imaging on TomoTherapy for high-fidelity dose calculations; (2) the dosimetric advantages and clinical implications of incorporating respiratory motion directly into treatment planning for lung SABR; (3) the impact of guided shallow breathing on tumour coverage and normal-tissue sparing in TomoTherapy; (4) the performance of a novel audiovisual biofeedback system in guiding shallow breathing on TomoTherapy; and (5) methods for rapid detection of 4DCT acquisition errors and quantifying their dosimetric implications. By integrating these insights, the thesis not only advances technical best practices for lung SABR on TomoTherapy but also empowers clinicians to make data-driven decisions that enhance treatment precision and ultimately improve patient outcomes.</p>