FIGURE 2.

Planning images derived from a patient treated with magnetic resonance-guided stereotactic ablative radiotherapy (SABR) for a left lower lobe tumour. a) A motion-encompassing target volume (red contour) derived from a planning four-dimensional computed tomography scan for free-breathing conventional SABR. b) The actual target volume (red contour) when a pre-treatment breath-hold magnetic resonance (MR) scan was acquired. The smaller target volume for magnetic resonance-guided SABR avoids risk of high-dose delivery to the stomach, and accurate delivery to smaller target volumes is ensured by continuous target tracking and automated beam triggering.