title: FDG-PET/CT-based gross tumor volume contouring for radiation therapy planning: an experimental phantom study.
abstract: As there is continuing controversy over the role of F-18-fluorodeoxyglucose (FDG)-positron emission tomography (PET)/CT-fused imaging in radiation therapy (RT) planning, we performed a phantom study to assess the feasibility of FDG-PET/CT-based gross tumor volume (GTV) contouring. The phantom set, consisting of an elliptical bowl and 6 spheres measuring from 10-37 mm in diameter, were filled with FDG to obtain 3 source-to-background ratios (SBRs) of 4, 8, and 16. The ratio to maximum intensity at 5% intervals was applied as the threshold for contouring. The ratio between contoured- and actual volumes (volume ratio) was calculated, and the threshold ratio was selected to provide a volume ratio close to 100%. To consider the clinical application, we applied the threshold value (maximum intensity × threshold ratio) for the largest 37-mm sphere to the 6 spheres. The threshold ratio and the volume ratio in 6 spheres with 3 SBRs were compared using the Friedman test. Threshold ratios ranged from 25-80%; they were higher for smaller spheres (p = 0.003) and lower SBRs (p < 0.001). The volume ratios with the threshold value for the largest 37-mm sphere were lower in smaller spheres (p = 0.010). These results suggest that smaller lesions and higher background activities require a higher threshold ratio and smaller lesions a lower threshold value. FDG-PET/CT-fused imaging should not be used as a single modality but rather to obtain supplemental information in RT planning. The contoured GTV should be adjusted based on clinical data including conventional images.
authors.affiliation: Department of Radiation Oncology, Faculty of Life Sciences, Kumamoto University, Japan.
authors.forename: Ryo
authors.initials: R
authors.lastname: Toya
authors.forename: Ryuji
authors.initials: R
authors.lastname: Murakami
authors.forename: Kuniyuki
authors.initials: K
authors.lastname: Tashiro
authors.forename: Morikatsu
authors.initials: M
authors.lastname: Yoshida
authors.forename: Fumi
authors.initials: F
authors.lastname: Sakamoto
authors.forename: Koichi
authors.initials: K
authors.lastname: Kawanaka
authors.forename: Shinya
authors.initials: S
authors.lastname: Shiraishi
authors.forename: Yuji
authors.initials: Y
authors.lastname: Nakaguchi
authors.forename: Naoko
authors.initials: N
authors.lastname: Tsujita
authors.forename: Natsuo
authors.initials: N
authors.lastname: Oya
authors.forename: Seiji
authors.initials: S
authors.lastname: Tomiguchi
authors.forename: Yasuyuki
authors.initials: Y
authors.lastname: Yamashita
mesh_terms: D019788:Fluorodeoxyglucose F18; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods*; D009369:Neoplasms / Q000473:pathology* / Q000532:radiotherapy*; D019047:Phantoms, Imaging; D049268:Positron-Emission Tomography / Q000379:methods*; D019275:Radiopharmaceuticals; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D061089:Radiotherapy, Image-Guided / Q000379:methods; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013382:Subtraction Technique; D014057:Tomography, X-Ray Computed / Q000379:methods*; D047368:Tumor Burden
chemical_list: D019275:Radiopharmaceuticals; D019788:Fluorodeoxyglucose F18