Purpose: Although [ 18 F] FDG-positron emission tomography (PET) provides vital information in diagnosing lung malignancies, the inherent uncertainties of standard uptake value (SUV) compromises its confidence. People have attempted to reduce this uncertainty by comparing the normal tissues, such as liver and spleen. However, those common reference structures may be inappropriate in some cases when pathological conditions exist. Hence, using alternative reference structures becomes valuable in

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... uch practice. The purpose of this study is to explore an alternative reference-correction method to reduce the inherent variation of SUV in the tumor or irradiated region. Methods: 106 analyzable FDG-PET scans from 49 cases who received lung SBRT for non-small cell lung cancer were retrospectively analyzed. The follow-up time ranges from 14.5 weeks to 113.2 weeks. The maximal SUV (SUVmax) was measured within the lung lesion or its corresponding region in post-SBRT. SUVmax was then corrected (or divided) by a reference SUV, or the mean SUV of the adjacent aorta, and results in the new SUVcmax. Results: SUVcmax of the positive group are significant higher than that of locally controlled cases (5.82 ± 3.10 vs. 1.45 ± 0.55, p = 0.026), while inconsequential differences were identified between the groups (p = 0.086). Respectively 85.2% and 96.3% of locally controlled cases post SBRT showed decreased values in the latter PET using SUVmax and SUVcmax. PET taken 24 weeks or sooner post-SBRT yielded higher uncertainties. Conclusion: Comparing with the conventional SUVmax, the alternative regional background-corrected SUV indicator, SUVcmax of PTV suggests a stronger correlation between low (<2.5 -3.0) values and the local tumor control post lung SBRT for NSCLC. However, FDG-PET images taken earlier than 24 weeks post-SBRT presents larger variations in SUV of the irradiated region due to underlying radiation induced inflammatory changes, and is not recommended for assessing local tumor control after lung SBRT.