The prospective study involved PET/MRI exams performed after FDG-PET/CT images were obtained for clinical evaluation. For each exam, PET parameters were determined, including maximum standardized uptake values (SUVmax) and metabolic tumor volume. Disease sites were assessed with PET/MRI and the results were compared with PET/CT.
Among the 18 patients evaluated, 14 had cervical cancer, two had vaginal cancer, one had vulvar cancer, and one had ovarian cancer. PET/MRI was obtained prior to therapy for five patients, midtherapy for three women, and after therapy for 10 women.
On the pretherapy exams, the SUVmax of the primary tumor as determined by PET/MRI and by PET/CT was similar (mean difference ± 10.55%). The metabolic tumor volume of the primary tumor on baseline imaging also was similar between PET/MRI and PET/CT (mean difference ± 19.96%).
The sites of disease identified by PET/MRI, including primary tumor and involved lymph nodes, corresponded with sites found on PET/CT. Similarly, in patients where post-therapy PET/CT found no evidence of disease, PET/MRI also demonstrated no evidence of disease.
A major advantage to PET/MRI is the synchronous acquisition of images, which avoids differences in patient position, bladder and rectal filling, and tumor growth, said lead study author Dr. Maria Thomas, PhD, chief resident in radiation oncology.
"Simultaneous PET/MRI may be especially valuable in comparing tumor boundaries between PET and various MRI sequences, in radiation treatment planning, in minimizing patient scan time when both PET and MRI are desired, in reducing radiation dose to patients, and in interpreting cases with indeterminate findings by providing co-localization of the two modalities," she added.