A practical review of magnetic resonance imaging for the evaluation and management of cervical cancer
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A practical review of magnetic resonance imaging for the evaluation and management of cervical cancer Emma C. Fields* and Elisabeth Weiss
Abstract Cervical cancer is a leading cause of mortality in women worldwide. Staging and management of cervical cancer has for many years been based on clinical exam and basic imaging such as intravenous pyelogram and x-ray. Unfortunately, despite advances in radiotherapy and the inclusion of chemotherapy in the standard plan for locally advanced disease, local control has been unsatisfactory. This situation has changed only recently with the increasing implementation of magnetic resonance image (MRI)-guided brachytherapy. The purpose of this article is therefore to provide an overview of the benefits of MRI in the evaluation and management of cervical cancer for both external beam radiotherapy and brachytherapy and to provide a practical approach if access to MRI is limited. Keywords: Cervical cancer, Magnetic resonance imaging, Radiotherapy
Introduction Cervical cancer is a leading cause of mortality in women worldwide [1]. The primary treatment of very early stage disease (IA1-IB1) is surgery and for more advanced disease (larger IB1-IVA) radiotherapy combined with chemotherapy [2–6]. Clinical staging based on physical exam combined with multimodality imaging is of utmost importance as it determines whether a woman is eligible for surgery and also describes the extent of the cancer for women who are not surgical candidates. Definitive radiation therapy of cervical cancer is one of the most challenging treatment situations in radiation oncology requiring application of high radiation doses to achieve tumor control. However, the geometrical distribution of target volumes in the pelvis with a central tumor positioned directly between radiosensitive organs (bladder, rectum, sigmoid and small bowel) and involved or at risk lymph nodes neighboring small bowel are challenging for external beam therapy. High radiation doses can therefore typically not be delivered by external beam radiotherapy alone and necessitate an additional brachytherapy boost. Traditionally, the brachytherapy boost has been delivered with tandem-based applicators using 2D x-ray
planning with a pear-shaped dose distribution prescribed to Point A. However, comparisons of point-based 2D planning with volumetric-based 3D planning show poor correlation between point doses and both coverage of clinical target volumes as well as doses to organs at risk (OARs), indicating a clear need for improved image guidance and soft tissue-based information to guide the planning process [7]. With its excellent soft tissue imaging characteristics, magnetic resonance imaging (MRI) now plays an important role in many aspects of tumor staging, planning and delivery of radiotherapy, post treatment response assessment and surveillance [8–10]. MRI is well known to have superior soft tissue imaging characteristics and shows excellent results in determining local disease extent compared to physical exam and other 3D
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