No abstract

Purpose The aims of this study were to: (1) estimate the volumetric and metabolic growth rate of non-small cell lung cancer (NSCLC), (2) evaluate disease progression prior to treatment, and (3) explore the effects of tumor growth rate and time to treatment (TTT) on survival outcome. Methods Patients with inoperable stages I–III NSCLC with serial pre-treatment PET/CT scans were eligible for this study. PET-derived metabolic tumor volumes (PET-MTV) and CT-derived gross tumor volumes (CT-GTV) were contoured using PET/CT information. Normalized standardized uptake values (NSUV) in tumors including the NSUVmean and NSUVmax were measured. Tumor growth rates expressed as doubling time (DT) were estimated using an exponential model. Pre-treatment disease progression defined as the development of any new site of disease on PET/CT and change in TNM stage (AJCC 7th ed.) were recorded. Growth rate and tumor progression were analyzed with respect to overall (OS) and progression free survival (PFS). Results Thirty-four patients with a median inter-scan interval (ISI) of 43 days and TTT of 48 days were analyzed. Tumor volumes showed remarkable inter-scan growth while NSUV did not increase significantly. The DT for PET-MTV, CT-GTV, NSUVmean and NSUVmax were 124, 139, 597, and 333 days, respectively. Pre-treatment disease progression occurred in 20.6% patients with longer ISI being a significant risk factor (OR = 1.027, p = 0.02). The optimal threshold ISI to predict progression was 58 days (4.8% vs. 46.2%, p = 0.007). Neither tumor growth rates nor TTT were significantly correlated to OS or PFS. Conclusions NSCLC displays rapid tumor volume growth whereas NSUVmean and NSUVmax are relatively stable over the same time period. Longer delays before initiation of treatment are associated with higher risk of pre-treatment disease progression.

Objective We have previously demonstrated that tumor reduces in activity and size during the course of radiotherapy (RT) in a limited number of patients with non-small cell lung cancer (NSCLC). This study aimed to quantify the metabolic tumor volume (MTV) on PET and compare its changes with those of gross tumor volume (GTV) on CT during-RT for 3D conformal radiotherapy (3DCRT) and stereotactic body radiotherapy (SBRT). Methods Patients with stage I–III NSCLC treated with a definitive course of RT ± chemotherapy were eligible for this prospective study. FDG-PET/CT scans were acquired within 2 weeks before RT (pre-RT) and at about two thirds of total dose during-RT. PET-MTVs were delineated using a method combining the tumor/aorta ratio autosegmentation and CT anatomy based manual editing. Data is presented as mean (95% confident interval). Results The MTV delineation methodology was first confirmed to be highly reproducible by comparing volumes defined by different physicians and using different systems (coefficiency >0.98). Fifty patients with 88 primary and nodal lesions were evaluated. The mean ratios of MTV/GTV were 0.70(−0.07~1.47) and 0.33(−0.30~0.95) for pre-RT and during-RT, respectively. PET-MTV reduced by 70% (62–77%), while CT-GTV by 41% (33–49%) (p< 0.001) during-RT. MTV reduction was 72.9% and 15.4% for 3DCRT and SBRT, respectively (p< 0.001). Conclusion PET-MTV reduced more than CT-GTV during-RT, while patients treated with 3DCRT reduced more than SBRT. RTOG1106 is using during-RT PET-MTV to adapt radiation therapy in 3DCRT.