Adaptive-Radiation Therapy Using Functional Magnetic-Resonance Imaging In Head and Neck Cancers

Abstract

Treatment strategies for locally-advanced head and neck cancers have evolved with a strong emphasis on treatment adaptation based on disease risk or intra-treatment response. Magnetic resonance imaging offers an ideal platform to perform adaptive radiotherapy as it is non-invasive, adds no additional radiation risk and allows superior soft-tissue definition to conventional CT-based methods. This thesis explored the role of functional-MRI for delivering adaptive radiotherapy for head and neck cancers.

This thesis analysed the treatment-related changes of two diffusion-weighted image sequences (ssEPI and RESOLVE) and demonstrated good concordance between the two sequences when assessing for disease response in the second week of radiotherapy. As part of the INSIGHT II trial, ssEPI was used to help dose-escalate for non-responding patients (change in ADC <15% in week 2 of chemo-radiotherapy) without compromising the dose to organs at risk such as parotid glands. There was a modest dose-sparing effect for low-risk and responding tumours.

However, there were no patients with residual disease in this study to validate the findings from the original INSIGHT study, as to whether an Apparent Diffusion Coefficient threshold of 15% (for ssEPI and RESOLVE) is able to stratify between responders and non-responders. Exploratory imaging biomarkers such as intra-voxel incoherent motion and T2* did not show any significant trends to stratify patients into risk groups or determination of treatment response.

The final chapter explores laryngeal motion and shows that laryngeal motion is most prominent in the cranio-caudal directions. However this motion is not deemed significant as the duration and frequency of swallow are limited. Individualised treatment target volumes, based on respiratory-related laryngeal motion, were created for radiotherapy-planning studies using intensity-modulated based methods. This approach significantly spared organs at risk such as carotid arteries. Analysis of intra-fraction swallow-related motions demonstrated no compromise in dose to the treatment target when treating smaller targets.