Abstract
PurposePrognostic significance of volumetric 18F-fluorodeoxyglucose (FDG) positron emission tomography/computer tomography (PET/CT) parameters in carbon-ion radiotherapy (C-ion RT) treated stage I non-small cell lung cancer, and need of histology-wise separate cut-off values for risk stratification were assessed.MethodsThirty-nine patients (29 men and 10 women, 71.9 ± 8.3 years) who underwent FDG PET/CT examinations before C-ion RT were retrospectively evaluated. FDG-PET parameters: standardized uptake values (SUVmax, SUVpeak, and SUVmean), metabolic tumor volume (MTV), and total lesion glycolysis (TLG), and clinicopathological variables were assessed for prognosis using Cox proportional hazards regression analysis. Mann-Whitney test compared medians of significant parameters between adenocarcinoma (AC) and squamous cell carcinoma (SCC), and Kaplan-Meier curves were plotted for median-based low- and high-risk groups.ResultsMedian follow-up period was 44.8 months. 1/2/3-year overall survival (OS), progression-free survival (PFS) and local control (LC) rates were 94.9/84.3/70.8, 82.1/69.2/58.4 and 97.3/85.7/82.3%. Multivariate analysis revealed age (hazard ratio, HR: 1.09; 95% confidence interval, CI: 1.0–1.19, p < 0.05) and MTV (HR 4.83, 95% CI 1.21–19.27, p < 0.03) predicted OS, and only MTV predicted PFS (HR 5.3, CI 1.32–21.35, p < 0.02) independently. Compared with AC, SCC had higher MTV (median, 6.625cm3 vs 0.2 cm3, p < 0.01). Single MTV cut-off based on overall cohort was insignificant in SCC for PFS (p > 0.02); separate cut-offs of MTV, 0.2 cm3 for AC (p < 0.03) and 6.625 cm3 for SCC (p < 0.05) were relevant.ConclusionAmong all FDG PET/CT parameters, only MTV beared prognostic ability for stage I NSCLC treated with C-ion RT, and its histological variation may need consideration for risk-adapted therapeutic management.
Highlights
Materials and methodsStage I non-small cell lung cancer (NSCLC) accounts for 15–20% of total NSCLC cases and surgery is the mainstay of treatment
Intraclass correlation coefficient (ICC) values were high for metabolic tumor volume (MTV) (ICC = 0.99–1) parameters compared to tumor size (ICC = 0.94–0.95). We know this was the first clinical study to evaluate the prognostic significance and predictive ability of the volumetric FDG positron emission tomography/computer tomography (PET/CT) parameters in stage I NSCLC treated by carbon-ion radiotherapy (Cion RT), and we found MTV was the only significant prognostic factor for overall survival (OS) and progression-free survival (PFS)
In our subgroup analysis based on histology, the median values of MTV were significantly different between AC and squamous cell carcinoma (SCC)
Summary
Stage I non-small cell lung cancer (NSCLC) accounts for 15–20% of total NSCLC cases and surgery is the mainstay of treatment. Due to unwillingness or inoperability because of difficult tumor sites, radiotherapy like stereotactic body radiation (SBRT) is considered alternative standard therapy. Carbon-ion radiotherapy (Cion RT) has emerged as an alternative therapeutic option and is currently practiced in a few centers of the world [1,2,3,4]. C-ion RT is expected to have better prognosis because of its high-focused beams to the cancer cells due to distal fall-off of Bragg peak, less lateral scatter, and doublestranded DNA breaks. Prognostic studies and treatment planning are required to prevent disease progression [4,5,6]
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