Magnetic Resonance Imaging-Guided Intracavitary Brachytherapy for Cancer of the Cervix

Abstract

To determine the feasibility and benefits of optimized magnetic resonance imaging (MRI)-guided brachytherapy (BT) for cancer of the cervix. A total of 20 patients with International Federation of Gynecology and Obstetrics Stage IB-IV cervical cancer had an MRI-compatible intrauterine BT applicator inserted after external beam radiotherapy. MRI scans were acquired, and the gross tumor volume at diagnosis and at BT, the high-risk (HR) and intermediate-risk clinical target volume (CTV), and rectal, sigmoid, and bladder walls were delineated. Pulsed-dose-rate BT was planned and delivered in a conventional manner. Optimized MRI-based plans were developed and compared with the conventional plans. The HR CTV and intermediate-risk CTV were adequately treated (the percentage of volume treated to >or=100% of the intended dose was >95%) in 70% and 85% of the patients with the conventional plans, respectively, and in 75% and 95% of the patients with the optimized plans, respectively. The minimal dose to the contiguous 2 cm(3) of the rectal, sigmoid, and bladder wall volume was 16 +/- 6.2, 25 +/- 8.7, and 31 +/- 9.2 Gy, respectively. With MRI-guided BT optimization, it was possible to maintain coverage of the HR-CTV and reduce the dose to the normal tissues, especially in patients with small tumors at BT. In these patients, the HR percentage of volume treated to >or=100% of the intended dose approached 100% in all cases, and the minimal dose to the contiguous 2-cm(3) of the rectum, sigmoid, and bladder was 12-32% less than with conventional BT planning. MRI-based BT for cervical cancer has the potential to optimize primary tumor dosimetry and reduce the dose to critical normal tissues, particularly in patients with small tumors.