Brief Summary: This trial studies how well magnetic resonance imaging (MRI)-guided internal radiation therapy (brachytherapy) works in treating participants with human papillomavirus (HPV) associated stage IB2-IV cervical or stage II-IVA vaginal cancer. Using MRI guidance during brachytherapy applicator placement may improve treatment planning in participants with cervical or vaginal cancer.

Detailed Description: PRIMARY OBJECTIVES: I. Determine whether MRI guidance during internal radiation therapy applicator placement improves the high-risk clinical target volume (HR-CTV) D90 (dose to 90% of the high-risk clinical target volume) rate compared to conventional guidance, with ultrasound and freehand technique, for patients with cervical and vaginal cancer. SECONDARY OBJECTIVES: I. Identify diffusion weighted MRI image features that can be used to identify sites of viable tumor following external beam radiotherapy as assessed by tumor aspirate cytology. II. Determine if diffusion weighted MRI findings are associated with immune infiltration as assessed by multi-spectral flow cytometry. III. Identify potential correlates between clinical outcomes (survival, progression) and these data objectives (brachytherapy dosimetry/therapeutic ratio, diffusion-weighted MRI imaging features, tumor aspirate cytology findings). IV. Define the financial costs and feasibility of an MRI-guided brachytherapy approach to determine the overall healthcare quality value (outcomes/cost) of this novel approach for application at other brachytherapy centers. OUTLINE: Participants undergo MRI scan during internal radiation therapy applicator placement.