Purpose: The purpose of this study was to evaluate the accuracy of PET imaging for predicting recurrence of disease and determining fields of radiation therapy for patients with lymphoma after first-line chemotherapy.
Methods and materials: The study population included 40 patients with lymphoma, newly diagnosed, staged and treated with either chemotherapy alone or combined modality therapy at this institution. PET findings were correlated with CT findings and radiation ports. Treatment and follow-up course were analyzed to determine patterns of failure.
Results: Twenty-eight of 40 patients (70%) were treated with chemotherapy alone, 12 of 40 (30%) were treated with combined modality therapy. Of the patients who received chemotherapy alone, 21 (75%) had a negative follow-up PET scan at the original site of disease, and 5 of these 21 (24%) recurred within the original site of disease. Of the patients who received combined modality therapy, 10 (83%) had a negative follow-up PET scan at the original site of disease and none recurred within the original site of disease.
Conclusions: A negative PET scan after completion of therapy does not exclude the presence of residual microscopic disease and does not indicate complete remission. A higher recurrence rate in patients who were treated with chemotherapy alone compared with combined modality therapy suggests that some of these patients may benefit from aggressive radiation therapy planned at initial staging. The radiation treatment volumes may be better planned from the initial staging PET study because a negative follow-up PET scan after chemotherapy cannot exclude residual microscopic disease.