Inflammatory changes and residual disease are difficult to distinguish after high dose, definitive radiotherapy of head and neck malignancies. FDG uptake located within a high dose field may more likely represent inflammatory changes, and FDG uptake outside of the radiation field could represent unsuspected and under treated disease. In situ knowledge of the precise radiotherapy fields, therefore, may be useful in distinguishing these etiologies. This study aimed to evaluate the clinical feasibility of rapid integration of radiation treatment field images during follow-up FDG PET/CT imaging. Twenty head and neck cancer patients who underwent radiation therapy were identified. A MIM based workflow was created which fused the radiation treatment CT, including the planning volumes and isodose curves, into the follow-up imaging. Two board certified physicians, blinded to treatment outcome, reviewed the follow-up exams, half with the treatment information and half without. Each exam was scored for recurrent or residual disease, confidence of the read and a qualitative assessment to the overall usefulness of the treatment plan. Interpretation accuracy improved from 80 to 90% with integration of the treatment plan. Similarly, the sensitivity improved from 71% to 86%, while the specificity increased from 85% to 92%. Confidence also increased by 0.7 on a 5 point scale for both readers. Data demonstrate the clinical feasibility of rapidly incorporating radiation treatment dosimetry into follow-up FDG PET/CT exams in patients with head and neck cancer. Preliminary results demonstrated a simple, efficient method which improved accuracy of interpretation and overall reader confidence.
Keywords: FDG PET/CT; Radiation treatment planning; inflammation; tumor recurrence.