F-18 FDG PET/CT (PET/CT) in pre-therapy planning and assessing response of cervical cancer treated with intensity modulated radiation therapy (IMRT)

Objectives To demonstrate the role of PET/CT in patients with cervical cancer for pre-therapy planning, assessing response to IMRT, and determining disease-free survival.

Methods Ten patients with initial FIGO stage III or IV (8/10) or recurrent cervical cancer (2/10) were followed since 2004 using PET/CT along with clinical examination. Patients were scanned on a GE Discovery ST in 2D mode for IMRT treatment planning, 2-6 months post-IMRT and every 3-6 months to assess for disease. Two patients did not receive a follow-up PET/CT scan. Initial treatment included IMRT and weekly sensitizing low-dose cisplatin for all patients, as well as brachytherapy for all patients except those with pelvic side-wall disease (8/10).

Results PET/CT was more accurate for initial staging than CT or pelvic MRI alone, and it determined the extent of the IMRT field in all 10 patients. PET/CT was particularly helpful in identifying paraaortic lymph nodes that did not meet CT size criteria, or were not imaged on pelvic MRI. Patients with no activity on first post-IMRT PET/CT scans remained disease free for over 5.5 years (2/8), while persistent activity either represented inflammation (2/8) or represented residual (1/8) or new disease (3/8). All but one patient with residual or new FDG-avid disease on the post-IMRT follow up scan passed away (mean survival 3.4 yrs). Overall, 5 year-survival using IMRT as primary treatment modality is 60% and disease-free survival is 40% (5 and 8 yrs).

Conclusions PET/CT provides more accurate staging than CT or pelvic MRI allowing for appropriate radiation field delineation. A negative post-IMRT PET/CT has a good negative predictive value and identifying new or residual hypermetabolism may have prognostic significance. These results need to be further strengthened by studying more patients along with learning new ways to accurately differentiate posttreatment inflammation from residual neoplasm.