Abstract
Image guidance and adaptive treatment approaches are increasingly used to deliver highly conformal radiation therapy (RT) for gynecologic cancer management. RT delivered with curative or palliative intent can be administered alone or combined with surgery or systemic treatments. Advanced treatment planning and delivery techniques such as intensity-modulated radiation therapy, including volumetric-modulated arc therapy and image-guided adaptive brachytherapy allow for highly conformal radiation dose delivery leading to improved tumor control rates and less treatment toxicity. Quality onboard imaging that provides accurate visualization of the target and surrounding organs at risk is a critical feature of these advanced techniques. As soft tissue contrast resolution is superior with magnetic resonance imaging (MRI) compared to other imaging modalities, MRI has been used increasingly to delineate tumors from adjacent soft tissues and organs at risk from the initial diagnosis to tumor response evaluation. Gynecologic cancers often have poor contrast resolution compared to the surrounding tissues on computed tomography scans, and consequently, the benefit of MRI is high. One example is in the management of locally advanced cervix cancer, where MRI guidance has been broadly implemented for adaptive brachytherapy. The role of MRI for external beam RT is also steadily increasing. MRI information is used for treatment planning, predicting and monitoring position shifts, and accounting for tissue deformation and target regression during treatment. The recent clinical introduction of online MRI-guided RT (MRgRT) is considered the next step in high-precision RT. This technology provides a tool to take full advantage of MRI not only at the time of initial treatment planning but for daily position verification and online plan adaptation as well. Cervical, endometrial, vaginal, and oligometastatic lesions of gynecologic cancer origin are increasingly being treated on MRI linear accelerator systems worldwide. This chapter summarizes the current state, early clinical experience, and future directions of MRgRT in the management of gynecologic cancers.