ABSTRACT
The treatment targets for brachytherapy universally consist of small volumes of soft tissue, whereby accurately distinguishing tumor boundaries and uninvolved tissues and organs at risk (OARs) of injury is paramount. In virtually all brachytherapy applications, tumor targets are best visualized, characterized, and defined using magnetic resonance imaging (MRI). The spatial encoding of MRI is based on variations in magnetic field in space and time. To this end, magnetic field gradients are switched on and off in an MRI sequence. When using MRI for brachytherapy planning, some additional issues may play a role. A brachytherapy applicator has to be MRI compatible, and free of metal if possible. Brachytherapy seeds, used in prostate cancer, contain nonferrous metal. Careful validation of sequences and regular quality assurance (QA) is therefore warranted, when using MRI to guide brachytherapy treatments. The first application of MRI in prostate brachytherapy has been to augment or replace computed tomography (CT) in postplanning dosimetric evaluation of low-dose rate (LDR) implants.
