Correlating Clinical Outcomes With Changes in Tumor Volume and 18F-FDG PET Characteristics During Radiation Therapy for Head and Neck Squamous Cell Carcinoma (HNSCC)

227; Table 1 All (nZ72) Incomplete response (nZ10) Complete response, (nZ62) P D GTVP -46 (-55, -40) -46 (-81, 13) -46 (-55, -40) .9 D GTVN -36 (-44, -28) -21 (-40, 11) -43 (-49, -29) .01 D SUVmax of GTVP -39 (-45, -33) -31 (-46, -13) -39 (-45, -33) .6 D SUVmax of GTVN -35 (-45, -28) -28 (-63, 12) -37 (-47, -31) .6 D SUVmean of GTVP -29 (-38, -23) -28 (-46, 7) -28 (-38, -20) .9 D SUVmean of GTVN -30 (-35, -23) -28 (-50, 12) -31 (-36, -20) .8 parameters were normalized to blood pool uptake. Treatment response and recurrence were assessed by diagnostic PET/CT at 12 weeks posttreatment, serial history/physical exam, and biopsy if indicated. Significance of relative changes from baseline was assessed by Wilcoxon signed rank test. Distribution of measurements between groups was compared by Mann-Whitney test. Results: Seventy-two patients were evaluated: 51 oropharynx (44 p16 positive, 2 p16 negative, 5 unknown), 4 oral cavity, 7 larynx, 4 hypopharynx, and 6 nasopharynx. Sixty-five received concurrent chemotherapy. Stage distribution was 1 stage I, 3 stage II, 10 stage III, 53 stage IVA, and 5 stage IVB. Median follow-up was 18 months (interquartile range 9.6-25). Table 1 shows median percent relative change (95% confidence interval) on intraversus pretreatment scans. Primary and nodal tumor volumes, SUVmax, and SUVmean decreased significantly from baseline (P<.0001). Except for GTVN, relative changes were not associated with complete response posttreatment. Twelve recurrences have occurred (3 locoregional, 5 locoregional and distant, 4 distant). Pretreatment tumor volumes and SUV parameters were not associated with outcome. Intratreatment SUVmax of GTVP (median 6.2 vs 8, PZ.05), SUVmean of GTVP (2.5 vs 4, PZ.02), SUVmax of GTVN (4.4 vs 7.2, PZ.02), and GTVN (7.2 vs 21.6 cc, PZ.004) were significantly lower for patients with complete treatment response and no subsequent recurrence. Conclusion: Tumor size and SUV decreased significantly after 20 Gy. Although this study is limited by sample size, the results suggest that lower intratreatment SUVmax and SUVmean of GTVP, SUVmax of GTVN, and nodal tumor volume are associated with improved outcome. Analyses are ongoing to assess whether metabolic tumor volume and other SUV parameters predict for clinical outcomes. Author Disclosure: Y.M. Mowery: None. I. Vergalasova: None. D.S. Yoo: None. S.K. Das: None. W. Hara: None. D.M. Brizel: None. 228 Metabolic Tumor Volume Changes Measured by F-FDG-PET/CT After 1 Cycle of Induction Chemotherapy Is an Early Predictor of Radical Chemoradiation Therapy Outcome in Head and Neck Squamous Cell Carcinoma K.H. Wong, L. Welsh, D. Mcquaid, A. Dunlop, I. Murray, Y. Du, S. Chua, R. Panek, A. Riddell, D.M. Koh, S. Bhide, C. Nutting, K. Harrington, and K. Newbold; The Institute of Cancer Research, Sutton and London, United Kingdom, The Royal Marsden NHS Foundation Trust, Sutton and London, United Kingdom Purpose/Objective(s): To assess the predictive value of F-FDG positron emission tomography/computed tomography (PET/CT) parameter changes during induction chemotherapy (IC) for response to radical chemoradiation therapy (CRT) in head and neck squamous cell carcinoma (HNSCC). Materials/Methods: This is an ongoing prospective, single-institution study in which patients underwent F-FDG-PET/CT with thermoplastic shell immobilization before and 2 weeks following each cycle of IC (first cycle, IC1; second cycle, IC2). Following IC, patients received radical CRT (65 Gy in 30 fractions) over 6 weeks with concomitant chemotherapy on days 1 and 29. Treatment response was assessed at 3 months from completion of CRT with clinical examination, magnetic resonance imaging, and F-FDG-PET/CT. Patients with evidence of residual or progressive disease were classed as nonresponders. Reductions in tumor SUVmax (maximum standard uptake value) and MTV (metabolic tumor volume with a pre-determined SUV threshold of 3.5) following IC were compared between responders versus non-responders with Mann-Whitney U test. The significance threshold was set at P<.05. Results: Twenty patients with stage III-IVA HNSCC were included in this preliminary analysis. The median age was 63 years (47-69). All patients underwent 2 cycles of IC except 3 patients who stopped after 1 cycle due to poor tolerance. One patient did not receive concomitant chemotherapy due to persistent myelosuppression. In 17 evaluable patients, there was no significant difference in the changes from baseline between IC1 and IC2 for MTV (PZ.80) and SUVmax (PZ.10), indicating that most metabolic response to IC was observed early with little changes with subsequent