MRI and MRS simulation

Radiotherapy (RT) is an eective local-regional treatment modality for cancers of all stages. Image-guided radiation therapy (IGRT) enables the precise delivery of a tumoricidal dose to the treatment volume to allow for dose escalation and hypo fractionation, while sparing the nearby critical organs and structures. Magnetic resonance imaging (MRI) has been widely used for target and critical structure delineation in radiation therapy treatment planning due to its superior so tissue contrast over computed tomography (CT) (Khoo et al. 2000; Buyyounouski et al. 2004). Studies demonstrated that it is possible to perform treatment planning dose calculation directly on MRI for intensity-modulated radiation therapy (IMRT) of prostate cancer (Chen, Price, Wang et al. 2004; Chen et al. 2007) and 3D conformal radiotherapy for the brain (Beavis et al. 1998) using commercially available treatment planning systems. Magnetic resonance spectroscopy (MRS) has recently garnered great interest in radiation oncology in the eld of target denition for radiotherapy treatment planning, and for evaluation of response and recurrence. Over the past two decades, MRS has moved from being a basic research tool into routine clinical use (Payne and Leach 2006). MRS is able to detect signals from low molecular weight metabolites such as choline and creatine that are present at concentrations of a few mM in tissue. Spectra may be acquired from single voxels, or from a 2D or 3D array of voxels using spectroscopic imaging (Payne and Leach 2006).