HIGH PRECISION IMAGE-GUIDED RADIOTHERAPY DELIVERY IN LUNG CANCER PATIENTS

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Abstract

Background Globally lung cancer is the leading cause of cancer mortality. Despite technological advances in radiotherapy over the past two decades, survival gains have been limited and the outcome remains poor. The aim of this thesis is to investigate high precision image-guided radiotherapy (IGRT) delivery in lung cancer patients. This work was conducted under the auspices of the Advanced Radiotherapy Technologies Network (ART-NET). Methods Different approaches to evaluating high precision IGRT have been undertaken. First, the ART-NET UK lung stereotactic ablative radiotherapy (SABR) survey was conducted, to provide an understanding of how centres use IGRT to deliver lung SABR. The second study involved assessing image guidance (cone-beam computed tomography, CBCT) from patients treated with lung SABR for the presence of ITACs and evaluating their impact upon treatment. The final study assessed the potential role of MRI as a form of image guidance. MRI was compared to CBCT for the identification and localisation of lymph nodes in patients undergoing radiotherapy for lung cancer. Results The UK lung SABR survey demonstrated that significant national variation exists in how CBCT is used for lung SABR IGRT and that almost half of centres do not have a protocol to manage ITACs. It also clear that there is geographical disparity in the distribution of centres commissioned to deliver SABR. In the second study, ITACs were observed on the CBCTs of 22% of patients. Most were minor. However, they are associated with unplanned physics and clinician review and significantly increase the set up time. The final study demonstrated no difference between CBCT and the DIXON water MRI sequence when compared for the purposes of lymph node identification and localisation. Despite this, observers felt the MRI images were of a higher quality and they had more confidence in their use compared to CBCT. Conclusions This thesis has investigated high precision image-guided radiotherapy delivery from both the perspective of both early and locally advanced lung cancer. The survey demonstrated that national guidance needs updating to advise on the optimal IGRT strategy and the management of ITACs. This has led to further work to investigate the inequitable distribution of SABR provision and the impact of patient travel time. The second study confirms that ITACs can be a resource burden and impact the workflow for lung SABR patients. There is a clear need to incorporate guidance on the management of ITACs into IGRT protocols. Work is underway to develop such guidance. The final study demonstrates that MR guidance for the localisation of lymph nodes during thoracic radiotherapy may be beneficial. To investigate this further I have developed a protocol to allow comparison of CBCT with MR images acquired upon the MR linac (MRL) for the purposes of localisation in locally advanced lung cancer. In summary, this thesis investigates high precision image-guided radiotherapy delivery for lung cancer and provides important data that will provide the basis for future efforts to improve outcomes.

Keyword(s)

ART-NET; SABR; image-guided radiotherapy; lung cancer

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