Abstract
The ability to accurately visualize and delineate tumor and surrounding normal tissue is an essential component of radical radiotherapy treatment planning and in non-thoracic sites has been improved by integrating MRI. This early work investigated and optimized different MRI sequences for potential use in thoracic radiotherapy planning. 15 patients with primary lung cancer were scanned using a 1.5 Tesla scanner (Magnetom Aera; Siemens) and radiotherapy planning scanner (Philips Brilliance CT Big Bore, Philips Medical Systems). An identical patient immobilisation board was used (Extended Wing Board; Oncology Systems Limited) for both scans. Multiple MRI sequences were investigated and optimised to give similarity to contrast CT scans (3- 4 mm slice thickness, whole thorax coverage and axial imaging). After reviewing the entire anatomic structure, ability to visualize the primary tumor, lungs, heart and oesophagus were scored using a 5-point system (1, unacceptable; 2, poor; 3, acceptable; 4 good; 5 excellent) and compared to CT (two tailed t-test). Respiratory triggered T2w SPACE (n=12) and T2w TSE (n=3) sequences suggest improved visualization of primary tumor (mean score 4.2 and 4.0) in comparison to CT (3.9), p> 0.05. T2w TSE, T1w TSE (n=3) and T1w 2-point DIXON (n=5, breath hold) sequences may enhance oesophageal (4.3, 3.7 and 3.6) and cardiac (3.3, 4 and 3.4) visualisation, compared with CT (3.0), p>0.05). CT (n=15) was the optimal imaging modality for viewing lungs (p< 0.05). T1w Cartesian VIBE (n=12, breath hold) provided no clear benefit over CT and diffusion-weighted single-shot-planar images (n=8) remain problematic due to image distortion. This preliminary study demonstrates the potential for MRI to improve the visualization of thoracic primary tumors, oesophagus and cardiac anatomy, all of which can be challenging to see on CT imaging, particularly in patients with collapse, consolidation or mediastinal tumor invasion.
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