Vaginal Metastasis of Colorectal Cancer Treated With Image-Guided Intracavitary-Interstitial Brachytherapy: A Case Report

Metastasis of a colorectal primary tumor to the vagina is an uncommon condition, and its treatment strategies have not been well established. Computed tomography (CT)-guided intracavitary-interstitial (IC-IS) brachytherapy uses a few interstitial needles, in addition to conventional intracavitary applicators (such as the Fletcher-Suit applicator or vaginal cylinder), and achieves conformal dose distribution to bulky and/or irregularly shaped tumors. Here, we report a first case of an oligometastatic vaginal tumor from the colorectum that was treated successfully with radiotherapy using CT-based IC-IS brachytherapy. External beam radiotherapy (EBRT), followed by four sessions of IC-IS brachytherapy, resulted in a satisfactory dose prescription to the target while sparing normal organs adjacent to the tumor. This led to radiological complete remission of the tumor over at least six months, with no severe adverse effects. This case indicates that radiotherapy using CT-based IC-IS brachytherapy may be a viable treatment option for metastatic vaginal tumors.