Differentiation of tumor recurrence from radiation-induced pulmonary fibrosis after stereotactic ablative radiotherapy for lung cancer: characterization of super(18)F-FDG PET/CT findings

• Published in: Annals of nuclear medicine 2013-04, Vol.27 (3), p.261-270
• Main Authors: Nakajima, Naomi, Sugawara, Yoshifumi, Kataoka, Masaaki, Hamamoto, Yasushi, Ochi, Takashi, Sakai, Shinya, Takahashi, Tadaaki, Kajihara, Makoto, Teramoto, Norihiro, Yamashita, Motohiro, Mochizuki, Teruhito
• Format: Article
• Language: English
• ISSN: 0914-7187; 1864-6433
• DOI: 10.1007/s12149-012-0682-4

Objective: Stereotactic ablative radiotherapy (SABR), also known as stereotactic body radiotherapy (SBRT), is now a standard treatment option for patients with stage I non-small cell lung cancer or oligometastatic lung tumor who are medically inoperable or medically operable but refuse surgery. When mass-like consolidation is observed on follow-up CT after SABR, it is sometimes difficult to differentiate tumor recurrence from SABR-induced pulmonary fibrosis. In this study, we evaluated the role of super(18)F-fluorodeoxyglucose positron emission tomography combined with computed tomography (FDG-PET/CT) in differentiating tumor recurrence from radiation fibrosis after SABR. Methods: Between June 2006 and June 2009, 130 patients received SABR for stage I non-small cell lung cancer or metastatic lung cancer at our institution. Fifty-nine patients of them were imaged with FDG-PET/CT after SABR. There were a total of 137 FDG-PET/CT scans for retrospective analysis. The FDG uptake in the pulmonary region was assessed qualitatively using a 3-point scale (0, none or faint; 1, mild; or 2, moderate to intense), and the shape (mass-like or non mass-like) was evaluated. For semi-quantitative analysis, the maximum standardized uptake value (SUV sub(max)) was calculated. Results: Sixteen of 59 patients had local failure. In recurrent tumor, the combination of intensity grade 2 and mass-like shape was most common (21/23; 91 %). By contrast, in cases of radiation fibrosis, the combination of intensity grade 0 or 1 and non mass-like shape was most common (48/59; 81 %). The SUV sub(max) of tumor recurrence after 12 months was significantly higher than that of radiation fibrosis (8.0 plus or minus 3.2 vs. 2.1 plus or minus 0.9, p < 0.001), and all tumor recurrence showed the SUV sub(max) > 4.5 at diagnosis of local failure. At greater than or equal to 12 months after SABR, these two variables, the combination of intensity 2 and mass-like FDG uptake or SUV sub(max) > 4.5 acquired a significant high predictive value of local recurrence, finding sensitivity 100 % and specificity 100 % for both of them. Conclusions: The combination of FDG uptake patterns and SUV sub(max) was useful for distinguishing tumor recurrence from radiation fibrosis after SABR.