MA13.09 Serial FDG and FLT PET/CT during Curative-Intent Chemo-Radiotherapy for NSCLC Impacts Patient Management and May Predict Clinical Outcomes

Abstract

FDG-PET/CT is the gold-standard for non-small cell lung cancer (NSCLC) diagnosis, staging and tumor delineation prior to chemo-radiation therapy (CRT). FDG-PET is superior to CT for subsequent response assessment. Sequential interim metabolic and proliferative tumor response assessment with FDG and 3'-Fluorothymidine (FLT) respectively, prior to and during CRT is novel and may predict outcome. Patients with FDG-PET-stage I-III NSCLC who were prescribed radical chemo-RT (60 Gy in 30 fractions @ 5/wk) were enrolled. FDG and FLT PET/CT scans were performed at baseline and at weeks 2 and 4 of CRT. Intra-treatment tumor response judged by reduction in FDG and FLT uptake was categorized as complete (CR)/partial response (PR), stable (SD) or progressive disease (PD) using EORTC criteria. Overall Survival (OS) and Progression Free Survival (PFS) were measured relative to intra-treatment scan dates and plotted using Kaplan-Meier curves. Univariate Cox regressions were used to calculate associations between 1. SUVmax of baseline FDG and FLT GTV and 2. intra-treatment FDG and FLT response with patient outcomes (OS and PFS). Sixty patients were recruited between 2009-13; male 62%; median age 66 years, adenocarcinoma (42%). Two-year OS and PFS were 0.51 and 0.26 respectively. Of 332 PET/CT scans analyzed, study scans provided additional information to FDGBL in 21 (35%) patients. Distant metastasis was detected in 3 patients on FLTBL and in 2 patients on FDG/FLTwk2 changed treatment intent to palliative. Loco-regional progression during RT was observed in 5 (8%) patients, prompting larger RT fields. FLTwk2 response (SD vs CR/PR vs PD) was associated with OS [HR (95%CI) 1 vs 2.02 (0.87, 4.65) vs 20.09 (4, 114), p=0.012] and PFS [1 vs 2.01 (0.92,4.37) vs 32.41 (3,348), p=0.024]. Associations between the baseline FDG and FLT SUVmax and patient outcomes were not significant, including OS where FDG SUVmax HR [95% CI] was 1.04 [0.98, 1.10], p=0.25 and FLT SUVmax HR [95% CI] was 1.07 [0.93, 1.22], p=0.33. Tumor response on FLTwk2 was associated with OS and PFS. The possible association between worse clinical outcomes and early suppression of FLT uptake during CRT may be a result of repair of tumor DNA damage. Baseline FLT, FLTwk2 and FDGwk2 detected rapid distant and loco-regional progression in 10 (17%) patients prompting changes in treatment intent and RT fields.