3'-Deoxy-3'-(18F) Fluorothymidine Positron Emission Tomography/Computed Tomography in Non-small Cell Lung Cancer...

The primary objective was to compare 3'-deoxy-3'-(¹⁸F) fluorothymidine (FLT) positron emission tomography (PET)/computed tomography (CT) uptake in 3 cohorts of stereotactic body radiation therapy (SBRT) patients: (1) pre-SBRT, (2) stable post-SBRT lung fibrosis, and (3) suspicious or proven local recurrence post-SBRT. The secondary objectives were to optimize FLT-PET imaging by comparing FLT uptake in respiratory-gated (4-dimensional) versus nongated (3-dimensional) FLT-PET scans.

Patients with early-stage non-small cell lung cancer planned or treated with SBRT at the institution with radiographic findings of fibrosis or recurrence were eligible for the study. All patients underwent imaging with FLT-PET/CT before SBRT in cohort 1 and at fibrosis or recurrence in cohort 2 and 3, respectively. The planned sample size was 20 patients in each cohort, with 60 patients total. FLT-PET standardized uptake value (SUV) variables including SUV_max, SUV_mean, SUV_peak, SUV₅₀, and SUV₉₅ were compared among the 3 cohorts using the Kruskal-Wallis test. The correlation of respiratory-gated and nongated FLT-PET SUV variables was performed using the Spearman correlation coefficient.

Forty-one patients were recruited for the study (20 in cohort 1, 16 in cohort 2, and 5 in cohort 3) between 2015 and 2019. The majority received a diagnosis of stage I lung cancer (86%), and the most common prescription was 48 Gy in 4 fractions (59%). Respiratory-gated FLT-PET was performed in 35 patients. The FLT SUV variables were well correlated between respiratory-gated and nongated scans (r = 0.8-1.0). The SUV_peak, SUV_mean, and SUV_max were significantly lower in the fibrosis cohort compared with the recurrence and pretreatment cohorts. The SUV₅₀ and SUV₉₅ values in the recurrence cohort were statistically similar to the pretreatment cohort.

FLT-PET/CT may be helpful in differentiating SBRT-related fibrosis from recurrence. Nongated FLT-PET/CT with reporting of SUV_max and SUV₉₅ values is recommended.