Use of F-FDG PET/CT Imaging for Radiotherapy Target Volume Delineation after Induction Chemotherapy and for Prognosis of Locally Advanced Squamous Cell Carcinoma of the Head and Neck.

Induction chemotherapy (ICT) before definitive chemoradiation (CRT) gives high response rates in locally advanced squamous cell carcinoma of the head and neck (LA-SCCHN). However, pre-ICT gross tumor volume (GTV) for radiotherapy (RT) planning is still recommended. As F-FDG PET/CT has an advantage of biological tumor information comparing to standard imaging methods, we aimed to evaluate the feasibility of F-FDG PET/CT-based post-ICT GTV delineation for RT planning in LA-SCCHN and to assess the prognostic value of PET parameters: maximum standardized uptake value (SUV), metabolic tumor volume (MTV) and total lesion glycolysis (TLG). 47 LA-SCCHN patients were treated with 3 cycles of ICT (docetaxel, cisplatin, and 5-fluorouracil) followed by CRT (70 Gy in 35 fractions with weekly cisplatin). Pre- and post-ICT PET/CT examinations were acquired. Planning CT was co-registered with post-ICT PET/CT and RT target volumes were contoured according to post-ICT PET. Post-ICT percentage decrease of SUV, MTV and TLG in primary tumor and metastatic regional lymphnodes (LN) was counted. Loco-regional failure patterns, 3-year progression free (PFS) and overall survival (OS) were evaluated. 3-year PFS and OS rates for study population were 67% and 61% respectively. 31.9% of patients progressed loco-regionally. All progress was localized in high-to-intermediate dose (60⁻70 Gy) RT volumes and none in low dose (50 Gy) volumes. Decrease of SUV ≥ 74% ( = 0.04), MTV ≥ 68% ( = 0.03), TLG ≥ 76% ( = 0.03) in primary tumor, and LN TLG decrease ≥ 74% ( = 0.03) were associated with PFS. Decrease of primary tumor SUV ≥ 74% ( = 0.04), MTV ≥ 69% ( = 0.03), TLG ≥ 74% ( = 0.02) and LN TLG ≥ 73% ( = 0.02) were prognostic factors for OS. According to our results, F-FDG PET/CT-based post-ICT GTV delineation is feasible strategy without negative impacts on loco-regional control and survival. Percentage decrease of metabolic PET parameters SUV, MTV and TLG has a prognostic value in LA-SCCHN.