Use of Functional Magnetic Resonance Imaging in Cervical Cancer Patients With Incomplete Response on Positron Emission Tomography/Computed Tomography After Image-Based High-Dose-Rate Brachytherapy

Purpose: To investigate the correlation between positron emission tomography/computed tomography (PET/CT) response and outcome in the era of magnetic resonance imaging (MRI)-based planning and to assess whether the addition of diffusion-weighted MRI (DW-MRI) could more accurately classify treatment response and prognosis.

Methods and materials: A retrospective chart review identified 244 consecutive patients with International Federation of Gynecology and Obstetrics stage IB1-IVA cervical cancer treated with concurrent chemoradiation, including high-dose-rate image-based brachytherapy, between 2007 and 2016. Image-based brachytherapy was delivered with 5 intracavitary/interstitial fractions, each 5 to 6 Gy per fraction.

Results: An complete response on posttreatment PET/CT (PET-CR) was discovered in 50 of 244 patients (20%) at a median interval of 3.3 months (range, 2.1-7.7 months) after treatment. After a median follow-up of 27 months, 2-year overall survival was 83% in all patients. Metabolic response significantly impacted 2-year overall survival (94% complete response on posttreatment PET/ CT vs 62.4% PET-IR, P < .001). Of those with a PET-IR, 16 of 50 patients (32%) suffered a local recurrence. A total of 27 of 50 patients with a PET-IR underwent DW-MRI; 11 of 27 posttreatment DW-MRI scans (40%) were interpreted as positive by central review (median apparent diffusion coefficient of 0.973 × 10^-3 mm²/s). Of the DW-MRI-positive patients, 9 of 11 (81.8%) suffered a histologically confirmed local recurrence, and 2 of 11 patients are without evidence of disease. Additionally, 16 of 27 DW-MRI studies were interpreted as negative, and 2 of 16 (12.5%) of these patients suffered a local recurrence. Diffusion-weighted MRI findings significantly impacted 2-year overall survival (83% negative DW-MRI vs 36% positive DW-MRI, P = .049).

Conclusion: Incomplete PET/CT response was documented in 20% of patients after image-based brachytherapy for locally advanced cervical cancer. Integration of DW-MRI helped accurately identify patients at risk for persistent disease and worse long-term outcome. The value of DW-MRI requires further validation in a large prospective dataset as this modality may allow earlier evaluation and salvage treatment in those with PET-IR.