Physiologic FDG-PET three-dimensional brachytherapy treatment planning for cervical cancer

Purpose: To compare conventional two-dimensional (2D) orthogonal radiography-based brachytherapy treatment planning for cervical cancer with a three-dimensional (3D) treatment planning technique based on ¹⁸F-fluoro-deoxyglucose-positron emission tomography (FDG-PET). Methods and Materials: Eleven cervical cancer patients were included in this prospective study that evaluated one tandem and ovoid brachytherapy procedure for each patient. The patient underwent FDG-PET of the pelvis to visualize the tumor followed by a second FDG-PET scan with the FDG isotope placed inside the tandem and ovoid applicators to visualize the treatment source positions for 3D treatment planning. The tumor volumes were delineated using a binary threshold technique in which the threshold FDG-PET image intensity was 40% of the peak tumor intensity. Results: FDG-PET provides a reliable estimate of the cervical cancer volume and 3D spatial relationship of the tumor to the tandem and ovoid applicators. The maximal bladder and rectal doses determined from the 3D FDG-PET dose-volume histograms were found to be higher than those obtained using 2D treatment planning. The minimal dose to the tumor volume defined by FDG-PET ranged from 50 to 475 cGy for treatment plans designed to deliver 650 cGy to Point A and exhibited an inverse correlation with tumor volume. Conclusion: Physiologic FDG-PET brachytherapy treatment planning is feasible and accurate relative to conventional 2D treatment planning. The use of FDG-PET offers a unique method for tumor visualization and identifies the limitations of conventional brachytherapy treatment planning for coverage of large tumors and estimation of the dose to normal structures. This technique has the potential for improving isodose tumor coverage for patients with cervical cancer while sparing critical structures.