Department of Radiology and Radiation Oncology, University of Mississippi Medical Center, USA
*Corresponding author: Ali Fatemi, Assistant professor Departments of Radiology and Radiation Oncology, University of Mississippi Medical Center, USA
Submission: September 02, 2017; Published: October 12, 2017
Magnetic resonance imaging (MRI) provides excellent soft tissue contrast, and in combination with its quantitative functional imaging capability, this modality is ideal for use in radiotherapy. MRI images, either used directly or fused with CT, play an increasingly important role in contouring gross tumor volume (GTV) and organs at risk (OAR) in radiation treatment planning (RTP) systems. The soft tissue contrast of MRI images provides more accurate tumor delineation than CT, although CT images have sufficient geometrical stability and electron density information for accurate radiation treatment planning. Many vendors now offer 70 cm wide-bore MRI systems with dedicated radiofrequency (RF) coils and immobilization devices for RTP simulation comparable to CT simulators.
Many groups are researching future applications of MRI simulation independent of CT and as a stand-alone modality for RTP and online guided radiotherapy. The aim of this paper is to discuss the major functional MRI pulse sequences used in RTP: dynamic contrast enhanced MRI (DCE-MRI), diffusion-weighted imaging (DWI) and magnetic resonance spectroscopic imaging (MRSI). We discuss the potential of these functional MRI techniques in different sites for tumor response evaluation and possible adaptive radiotherapy.
Keywords: MRI, Adaptive radiation therapy, MRI guided radiation therapy, quantitative imaging
Abbreviations: MRI: Magnetic Resonance Imaging; ADC: Apparent Diffusion Coefficient; GTV: Gross Tumor Volume; OAR: Organs at Risk; RTP: Radiation Treatment Planning; UTE: Using ultra-Short Echo; TPS: Treatment Planning System; RF: Radiofrequency; DCE-MRI: Dynamic Contrast enhanced MRI; DWI: Diffusion Weighted Imaging; MRSI: Magnetic Resonance Spectroscopic Imaging; DRRs: Digitally Reconstructed Radiographs; HDR: High Dose radiation rate IMRT: Intensity Modulated Radiation Therapy; VMAT: Volumetric Modulated Arc Therapy; FSRT: Fractionated Stereotactic Radiotherapy; SRS: Stereotactic Radiosurgery; RT: Radiotherapy; TCP: Tumor Control Probability; CT: Computed Tomography; IGRT: Image Guided Radiation Therapy; TWIST: Time Resolved Angiography with Interleaved Stochastic Trajectories; MRA: Magnetic Resonance Angiography; ROI: Regions of Interest; ADC: Apparent Diffusion Coefficient; 1H: Hydrogen; 31P: Phosphorus -31; 19F: Fluorine-19; 13C: Carbon-13; SVS: Single Voxel Spectroscopy; CSI: Chemical Shift Imaging; NAA: N-Acetylaspartate; FRT: Fractionated Radiotherapy; GBM: Glioblastoma; FLAIR: Fluidattenuated Inversion Recovery; AVMs: Arteriovenous Malformations; PDV: Prescribed 95% Isodose Volume; PRM: Parametric Response Map; PFS: Progression Free Survival; PCA: Principle Component Analysis; BOLD: Blood Oxygen Level Dependent; USPIO: Ultra Small Particle Iron Oxides; CBV: Cerebral Blood Volume; CBF: Cerebral Blood Flow; MIT: Mean Transit Time; SNR: Signal to Noise Ratio