WE‐A‐217A‐07: Predicting Residual Disease for NSCLC Using Pre‐Radiotherapy 4D PET/CT

Abstract

Purpose: To quantify PET treatment response using a novel image registration approach, and to investigate the impact of 4D PET/CT pre‐ radiotherapy scan for predicting residual high‐uptake areas toward dose‐ boosting in adaptive radiotherapy. Methods: 3D and 4D FDG‐PET/CT scans were obtained from ten patients with non‐small cell lung cancer (NSCLC) for approximately two weeks before radiotherapy (pre‐RT) and approximately one month after therapy (post‐RT). The 4D scan was taken immediately following a 3D PET scan. The areas of high uptake in the pre‐ RT scans were aligned with those in the post‐RT scans using a novel rigid‐ penalized deformable registration. The global lung bronchi and chest wall were non‐rigidly transformed to minimize the respiration effects while the target lesion is rigidly transformed to preserve the volume and SUV values. A region of interest (ROI) was defined by a threshold of 40% of the maximum SUV for both 3D and 4D PET scans. The maximal SUV within the ROI were measured. Volumetric overlap fraction (VOF) was calculated as the overlap volume of pre‐RT and post‐RT target volumes divided by the residual volume in the post‐RT scans. Results: The maximal SUVs for 4D pre and post PET have a 16.3% increase compared to those in 3D PET. The pre‐to‐post maximal SUV variations showed 57% lesions has nontrivial residual uptake (SUVmax>2.5) for 3D PET, and 64% for 4D PET. The results of the VOFs showed that the residual metabolic‐active areas are mainly located within the primary tumor volume, 92% for 3D and 89% for 4D. Conclusions: Residual metabolic‐active areas have strong physiological and geometric correspondence to the primary tumor. With better signal recovery than standard 3D PET, high uptake areas of 4D PET pre‐RT can predict areas where residual metabolic activity will be found after radiotherapy.