Once treated, patients are often restaged to determine the effectiveness of the treatment. A follow-up whole-body PET/CT scan can help evaluate whether the therapy was effective and can be particularly useful in helping the physician detect residual disease.
Before PET/CT, it was extremely difficult to monitor patients to see if the lymphoma had returned. Multiple CT scans would have to be done to capture images of the whole body and anatomical imaging merely identified changes in tumor size. In lymphoma, the tumor's glucose metabolism falls very rapidly after effective chemotherapy and PET/CT imaging can detect an increase or decrease in glucose utilization. Often, lymphoma tumors are large in diameter and do not immediately shrink to normal size after treatment. Physicians utilize PET/CT imaging to characterize a residual mass, or determine if active tumor cells remain within the scar tissue.
Early studies have shown that PET/CT may also identify patients who are more likely to achieve remission and less likely to relapse, by showing a characteristic pattern of reduction in glucose uptake in the abnormal lymph nodes half-way through and during planned chemotherapy. A negative PET/CT scan does not mean that treatment should be stopped, but it predicts a superior outcome to a positive PET/CT scan at mid treatment.
The treatment of lymphoma has been one of the true cancer success stories of the last 20 to 30 years. Continued improvements in chemotherapy and radiotherapy have resulted in better survival rates.
PET/CT can be used to image tumor response to therapy and to detect recurrence in treated lesions.