(S002) Prognostic Value of Intraradiation Treatment FDG-PET Parameters in Locally Advanced Oropharyngeal Cancer

Erqi L. Pollom, MD, Jie Song, PhD, Madhu Sudhan, Benjamin Y. Durkee, Sonya Aggarwal, BA, Rie von Eyben, Timothy T. Bui, BS, Ruijiang Li, PhD, Billy Loo, Quynh-Thu X. Le, Wendy Y. Hara, MD; Stanford University

BACKGROUND: To determine whether fluorodeoxyglucose (FDG) positron emission tomography (PET) parameters measured at an early time point during radiation for locally advanced oropharyngeal cancer (OPC) correlate with outcomes.

METHODS: Patients with stage III–IVB, intact OPC who were treated with definitive radiation with curative intent were included in this study if they underwent both pre- and midtreatment PET-computed tomography (CT) planning scans in our department. The treatment-planning CT was registered with the PET from the same session, and the metabolic tumor volume (MTV) was extracted from within the primary and nodal tumor volumes contoured by the treating physician. MTV was defined as the volume with standardized uptake value (SUV) > 2.5. MTV velocity was defined as the difference between pre- and midtreatment nodal MTV divided by time elapsed between these two scans. Extraction of imaging features was performed using MATLAB. 

RESULTS: In total, 60 patients who fulfilled the inclusion criteria were treated from February 2009 to January 2014 at Stanford. Median age was 59 years (range: 27–83 yr). The p16 status was positive in 51 patients, negative in 8 patients, and unknown in 1 patient. Nine patients received induction chemotherapy, and 59 patients received concurrent chemotherapy (cisplatin: n = 26; cetuximab: n = 25; carboplatin: n = 8). A total of 25 patients had a > 10-year smoking history. 

Patients were treated to a median dose of 70 Gy (range: 63.6–70 Gy, in 30–35 fractions). Patients underwent a planning PET at a median of 11 days (range: 2–26 d) prior to radiation start and an intratreatment planning PET after receipt of a median of 16 fractions (range: 10–22 fractions).

Median pretreatment MTVs for the entire cohort at the primary, nodal, and combined primary and nodal sites were 16.7 cc (range: 0.9–143.0 cc), 11.5 cc (range: 0–195.1 cc), and 32.7 cc (range: 2.0–225.2 cc), respectively. Median intratreatment MTVs for the entire cohort at the primary, nodal, and combined primary and nodal sites were 7.6 cc (range: 0.4–150.2 cc), 3.8 cc (range: 0–95.6 cc), and 14.7 cc (range: 0.3–150.2 cc), respectively. 

Median follow-up was 17 months (range: 2–63 mo). One-year overall survival was 98%. Age, smoking status, chemotherapy, and stage did not predict for survival. For the entire cohort, there was a trend for worse survival with less metabolic response, as measured by MTV velocity (P = .09; hazard ratio [HR] = 1.6). Within the p16+ patients, less metabolic response at the combined primary and nodal sites was a significant predictor for worse survival (P = .03; HR = 2.2).

CONCLUSION: Metabolic response during radiotherapy predicts for survival in p16+ OPC patients and may help in risk stratification of these patients for potential treatment de-intensification.

Proceedings of the 97th Annual Meeting of the American Radium Society - americanradiumsociety.org