Respiratory Adaptive Computed Tomography: Feasibility Study on Real-Time Gated 4DCT for Lung Cancer Radiotherapy

This study does not involve a therapeutic intervention as standard radiation therapy treatment will be prescribed. This study involves one additional 4DCT scan (i.e. the Real-Time Gated 4DCT scan) acquired immediately before or following the conventional 4DCT scan. This will take place on the day of the patient's treatment simulation, as per the current standard of care. The scanning sequence (i.e. conventional first versus gated first) will be randomised. The Real-Time Gated 4DCT is anticipated to take longer than the conventional 4DCT scan, due to its gated (beam-pause) nature. However, upper limits for timing will be implemented in the software, and the scan aborted for highly erratic breathing traces that would not benefit from a Real-Time Gated 4DCT scan.

Four-dimensional computed tomography (4DCT) is considered the standard of care for modern high-precision stereotactic ablative body radiotherapy (SABR) techniques. Clinical 4DCT works by acquiring CT slices and breathing data synchronously as the patient moves through the rotating X-ray imager. The CT slices are sorted into 5-10 'phase images' (mid-exhale, peak-exhale, mid-inhale, peak-inhale, etc.) and stitched together to form a 3D+breathing induced tumour/organ motion or '4D' representation of the breathing anatomy. Current best practice in radiation therapy is for clinicians to perform manual delineation or 'contouring' of lung tumours on one or more 4DCT phase images to ensure proper coverage by the treatment beam despite breathing motion. In the presence of irregular breathing, mismatches arise between CT slices that are in the same breathing phase but imaged at different couch positions. As a result, the images produced suffer from various kinds of discontinuities including truncation, duplication or overlap. Yamamoto found that irregular breathing caused at least one error \>4mm in 90% (45 out of 50) abdominal and thoracic patient scans. The main consequence of 4DCT image errors is that they can introduce tumour volume and position uncertainties as large as 30% between different 4D phase bins or different observers. This can potentially reduce the likelihood of tumour control by up to one-third and lead to unnecessary irradiation of healthy lung tissue, contributing to major dose-limiting side effects like radiation pneumonitis, which is symptomatic in up to 30% of patients and fatal in 2%. The proposed solution is Real-Time Gated 4DCT using prospective regularity gating, which will be implemented for the first time on lung cancer patients. The Real-Time Gated 4DCT method detects and then pauses the CT beam during irregular breathing events. We will analyse the patient's breathing pattern to prospectively gate acquisition in real-time. Real-time gated 4DCT ensures that the X-ray imager is switched on only when the breathing is regular; the scan gets paused otherwise. The benefits for the patient of gating a 4DCT scan have been demonstrated in previous studies: * a reduction of breathing motion errors by 50% * a reduction of imaging dose. Delineation of tumours and organs in CT scans is the first step in a lung cancer patient's radiation therapy journey. Accurate delineation is pivotal to patient outcomes because errors propagate throughout treatment and can lead to radiation dose missing parts of the tumour or unnecessarily irradiating healthy tissue or organs. Unfortunately, the most important imaging modality used for the delineation of lung cancers, 4DCT, is error prone. Radiation Oncologists (ROs) are faced with an enormous challenge and are required to delineate tumours when 90% of clinical scans suffer severe imaging errors. These errors obfuscate the true tumour position/shape and reduce the chance of tumour control by up to one Покажи пълното описание...

Inclusion Criteria: * 18 years or older * Have the ability to give informed consent * A diagnosis of lung cancer with an indication for radiation therapy * Radiation therapy treatment involving the acquisition of a 4DCT scan for treatment planning Exclusion Criteria: * Pregnant women * Patients \<18 years * Patients who in the opinion of the treating physician could not tolerate the extra time on the CT couch for an extra scan