Tangel Chang DO, Presenter: Nothing to Disclose

Carryn Anderson MD, Abstract Co-Author: Nothing to Disclose

Michael M. Graham MD, PhD, Abstract Co-Author: Nothing to Disclose

Gerry Funk MD, Abstract Co-Author: Nothing to Disclose

Anna Button MPH, Abstract Co-Author: Nothing to Disclose

Yusuf Menda MD, Abstract Co-Author: Research Grant, Advanced Accelerator Applications

Wenqing Sun MD, PhD, Abstract Co-Author: Nothing to Disclose

Michael Marquardt BS, Abstract Co-Author: Nothing to Disclose

John M. Buatti MD, Abstract Co-Author: Nothing to Disclose

FDG-PET/CT is used for response assessment post-radiotherapy (RT) in head and neck squamous cell carcinoma (HNSCC), but the false positive (FP) rate is approximately 50%. The positive predictive value (PPV) remains low due to inability to differentiate between inflammation and malignancy. We hypothesize that the SUVmax slope when imaged at 60-, 90-, and 120- min after FDG injection (Triphasic PET/CT) would better predict recurrence because tumors should increase uptake between 60- and 120- min whereas nonmalignant, inflammatory uptake will plateau or decrease. The goal is to improve the diagnostic accuracy of FDG-PET/CT as a post-RT response assessment tool.

Patients with HNSCC were prospectively enrolled to undergo Triphasic 3-month post-RT PET/CT. In addition to our standard whole-body PET scan at 90-min, enrolled patients had a PET of the head and neck with low-dose CT at 60- and 120-min. SUVmax was measured for the three time points and the delta change in SUVmax slope, [(SUVmax 120-SUVmax 90)-(SUVmax 90-SUVmax 60)], was calculated. Standard outcomes are defined by the 90 min PET/CT as equivocal (EQ), false negative (FN), true negative (TN), true positive (TP), and FP, and the delta change in SUVmax slope between 60-, 90-, and 120-min was evaluated to differentiate between TP and FP.

57 HNSCC patients were eligible for analysis. Median follow-up post-RT was 15.4 months. 16% recurred at the primary site. There were 8 EQ, 3 FN, 38 TN, 4 FP, and 4 TP scans. In those with positive scans, (TP + FP) defined by the 90 min time point, the delta change in SUV max slope could differentiate TP from FP in all cases and was statistically significant using the Wilcoxon Rank Sum Exact test as a predictor of outcome (p=0.02).

Analysis of the prospective Triphasic FDG-PET/CT trial demonstrated that the delta change in SUVmax slope at the 60-, 90-, and 120- min post FDG injection allows improved differentiation between inflammation and malignancy in HNSCC patients. Utilizing the SUVmax slope along with the standard SUVmax at a single time point, the FPs induced by inflammation may be better identified. This method improves the PPV, and enhances the accuracy of FDG-PET/CT.

PET/CT post-RT for HNSCC has PPV of 50%, resulting in significant anxiety and morbidity from biopsy/dissection. Delta change in SUVmax slope of triphasic PET/CT may accurately differentiate TP vs FP.

Chang, T, Anderson, C, Graham, M, Funk, G, Button, A, Menda, Y, Sun, W, Marquardt, M, Buatti, J, A Phase II Prospective Trial of Triphasic PET/CT: Delta Slope of SUVmax Differentiates True Positive from False Positive Scans at the Primary Site after Radiation in Head and Neck Squamous Cell Carcinoma.  Radiological Society of North America 2014 Scientific Assembly and Annual Meeting, - ,Chicago IL. http://archive.rsna.org/2014/14007354.html