Nandita DeSouza1
1Imaging, Institute of Cancer Research, Sutton, Surrey, United Kingdom
Synopsis
MRI is the fundamental imaging modality in the management pathway of cervical cancer. Its use is crucial for early diagnosis, for tumor staging, to provide prognostic information, to monitor the effects of treatment and to follow-up patients for detection of disease recurrence.
TARGET AUDIENCE
Radiologists with an
interest in gynaecological oncology
OBJECTIVES
To understand why, when and how to image cervical tumours Epidemiology and Screening
Worldwide, cervical cancer is the second most common cancer amongst women. In developed countries, screening programmes with papanicolau (pap) smear cytology have contributed greatly to early detection of cancer and led to a dramatic reduction in mortality. Following the detection of abnormal cells, colposcopy is carried out and a cone or loop biopsy specimen obtained for histopathology to determine the grade of CIN or CGIN. Left untreated, 70% of CIN 3 and CGIN 3 (severe dyskaryosis) lesions will progress to invasive cervical cancer [2]. Tumours are usually squamous (~70%) or adeno carcinomas (~30%) arising from the cervical epithelium in a background of intraepithelial neoplasia. Unusual histological subtypes such as minimal deviation adenocarcinoma, lymphoma and neuroendocrine tumours are rare. MRI for Staging disease
The most widely used staging system for cervical cancer is the Federation Internationale de Gynécoligic et Obstétrique (FIGO) classification [1]. In early stage disease, the most important information from imaging is whether or not tumor extends to the parametrium as this separates a surgical from a non-surgical management approach [2]. MRI is superior to any other imaging modality for evaluating disease extent [3] and is now an integral part of preoperative assessment of cervical cancer, in monitoring response to treatment and in detection of recurrence. Fast spin-echo T2-weighted sequences provide best image contrast for delineating extent of disease within the cervix. Volume (3-D) imaging also provides the information necessary to calculate tumour volumes, which is of prognostic significance. Recently, diffusion-weighted MRI has shown higher accuracy than T2-weighted imaging alone for tumour detection [14]. PET with 2-[fluorine-1]fluroro-2-deoxy-D-glucose (FDG) may also be used in cervical cancer staging and follow-up and is useful in evaluating lymph node involvement and for detecting distant metastases [3;4;5]. Although 3T scanners offer increased SNR, their increased field inhomogeneity means that their advantage over 1.5T remains debatable. The resolution of the primary tumour on MR imaging may be further improved by using endocavitary receiver coils, which are advantageous when planning fertility-sparing surgery (6). MRI as a prognostic biomarker
Tumor size or volume has long been recognised strong prognostic biomarker: a retrospective study of 275 surgically treated women with Stage Ib-IIb cervical cancer with negative lymph nodes showed a strong correlation between tumor diameter and prognosis [7]. ADC quantified from diffusion-weighted images is also indicative of tumor type and grade (8). More recently, radiomic evaluation of these data appears to predict recurrence following optimal conventional treatment (9). MRI for treatment planning
MRI is now routinely used for brachytherapy planning but requires MRI compatible applicators to minimize artefacts and distortions (10). With MR Linac systems now available, planning stereotactic external beam radiotherapy is feasible and will form an important application of MRI for this disease in future (11). MRI for follow-up
Serial MR imaging may be used before and after primary radiation therapy to assess tumor response [98]. DCE-MRI quantitative parameters of the exchange rate constants Ktrans and Kep (and semi-quantitative parameters of peak time, slope, maximum slope and contrast enhancement ratio) after 2 and 5 weeks of treatment have been shown to correlate significantly with percentage tumor regression [12] and also provide early prediction of primary tumor control and disease-free survival [12]. Tumor volumes and regression ratios as early as 2 weeks into radiotherapy have been shown to correlate strongly with local recurrence: a volume of >40 cm3 and a ratio of >20% from baseline at 1 month had an 89% sensitivity and an 87% specificity for predicting local recurrence [13]. An increase in ADC derived from DW-MRI seen after 15 days of therapy has also been shown to indicate response [14]. Pretreatment ADCs for complete responders have been shown to be significantly lower than those of partial responders with a negative correlation between pretreatment ADCs and percentage size reduction after 2 months of chemoradiation [14]. There is also a role for 18FDG-PET in response assessment: when residual metabolically active disease 3 months after completion of treatment is identified, additional therapy may be warranted [15].Acknowledgements
No acknowledgement found.References
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