Design of a Whole-Body Radio Frequency Coil for image-guided radiotherapy treatment in a MRI-LINAC system

INTRODUCTION: Radiotherapy is a primary cancer treatment modality. However, targeting a radiation beam on tumours in moving organs such as liver, stomach or lungs, without damaging healthy tissue can be challenging. For this reason, Magnetic Resonance Imaging (MRI) and Linear Accelerator (LINAC) are being combined as a MRI-LINAC, a new image-guided radiotherapy treatment capable to both image and accurately treat the patient simultaneously. In previous work [1-3], a 1T MRI magnet and gradient system with a large central gap (50 cm) was introduced, wherein the LINAC and the patient can be placed in an ‘in-line’ (Figure 1, left) or a perpendicular configuration (Figure 1, right). Both configurations are considered, as they have different advantages and disadvantages [3]. A radiofrequency (RF) transmit volume coil was developed to fit into this specific system. The combination of MRI with radiotherapy introduced new constraints that had to be considered in the design of the coil. An unobstructed path for the LINAC beam to target the patient had to be combined with the requirement of providing a good RF field homogeneity over the whole field of view. Results of simulations and experiments showed that a good uniformity can be achieved.