FDG-PET imaging for the assessment of physiologic volume response during radiotherapy in cervix cancer.

PURPOSE: To evaluate the physiologic tumor volume response during treatment in cervical cancer using 18F-fluorodeoxyglucose positron emission tomography (FDG-PET). PATIENTS AND METHODS: This was a prospective study of 32 patients. Physiologic tumor volume in cubic centimeters was determined from the FDG-PET images using the 40% threshold method.
RESULTS: The mean pretreatment tumor volume was 102 cm3. The mean volume by clinical Stages I, II, and III were 54, 79, and 176 cm3, respectively. After 19.8 Gy external irradiation to the pelvis, the reduction in tumor volume was 29% (72 cm3). An additional 13 Gy from high-dose-rate (HDR) brachytherapy reduced the mean volume to 15.4 cm3, and this was subsequently reduced to 8.6 cm3 with 13 Gy additional HDR brachytherapy (26 Gy, HDR). Four patients had physiologic FDG uptake in the cervix at 3 months after the completion of therapy. The mean time to the 50% reduction in physiologic tumor volume was 19.9 days and after combined external irradiation and HDR to 24.9 Gy.
CONCLUSION: These results indicate that physiologic tumor volume determination by FDG-PET is feasible and that a 50% physiologic tumor volume reduction occurs within 20 days of starting therapy.