Stereotactic Ablative Radiation Therapy for Lung Oligometastases: Predictive Parameters of Early Response by 18 FDG-PET/CT.

OBJECTIVES: The objective of this study was to investigate fludeoxyglucose F 18 positron emission tomography/computed tomography (18 FDG-PET/CT) parameters as predictive of response after stereotactic ablative radiotherapy (SABR) for lung oligometastases.

METHODS: The inclusion criteria of the current retrospective study were as follows: (1) lung oligometastases treated by SABR, (2) presence of 18 FDG-PET/CT before and after SABR for at least two subsequent evaluations, (3) Karnofsky performance status higher than 80, and (4) life expectancy longer than 6 months. All patients were treated with a biologically equivalent dose of at least 100 Gy with an alpha/beta ratio of 10. The following metabolic parameters were semiquantitatively defined: maximum standardized uptake value (SUVmax ), mean standardized uptake value (SUVmean ), metabolic tumor volume, and total lesion glycolysis.

RESULTS: A total of 50 patients met the inclusion criteria, for a total of 70 lung metastases. The pre-SABR median SUVmax was 6.5 (range 4-17), the median SUVmean was 3.7 (range 2.5-6.5), and the median metabolic tumor volume was 2.3 cm3 (0.2-31 cm3 ). The following metabolic parameters were significantly related to complete response at 6 months: SUVmax less than 5 (p < 0.001) and SUVmean less than 3.5 (p = 0.03). ΔSUVmax at 3 to 6 months was +126% for lesions with in-field progression versus -26% for the remaining lesions (p = 0.002). ΔSUVmean at 3 to 6 months was +15% for lesions with in-field progression versus -26% for the remaining metastases (p = 0.008).

CONCLUSIONS: In the current analysis, complete response from lung metastasis at 6 months after stereotactic body radiation therapy was significantly associated with both the maximum and mean values of pre-SABR 18 FDG-PET/CT SUV. Longer-term trials are strongly advocated to improve the personalization of the monitoring of tumor response in patients with lung oligometastases and, consequently, monitoring of the cost-effectiveness of the health care.