Histology Predicts Changes in Standard Uptake Value (SUV) and Radiographic Response After Stereotactic Body Radiotherapy (SBRT) in Stage I Non-small Cell Lung Cancer

Abstract

To evaluate the correlation among positron emission tomography (PET) SUV maximum values, CT volumetric response, and tumor histology in patients treated with SBRT for Stage I non-small cell lung cancer (NSCLC). Medical records of 68 consecutive patients with 75 Stage I NSCLC lesions were analyzed after SBRT. All patients had PET/CT scans prior to SBRT. Patients had a post treatment CT scan at 6 weeks and a PET/CT at 3 months. Alternating CT and PET scans were obtained every 3 months thereafter. Pre and post treatment CT volumes and PET SUV maximum values were measured. Patients received 45-54 Gy in 3-5 fractions, given twice a week. Treatments were prescribed to an isodose line ranging from 75%-95%. The median overall survival was 41 months, with a median follow-up of 10 months. Local control for this cohort was 97% with 2 patients failing at the original site of disease. In both cases, tumors were treated to 45 Gy in 5 fractions. When pre- and post-treatment gross tumor CT volumes were compared, adenocarcinoma histology had less relative volumetric reduction than squamous tumors (95% CI: 22-97%, p < 0.001) at 1.5 and 3 months, indicating a faster radiologic response for squamous cell carcinoma. Similarly, when pre- and post-treatment PET maximum SUV were compared, adenocarcinoma had a smaller relative decrease in maximum uptake at 3 months than squamous histology (p-value < 0.0001). We further explored the relationship between the response by CT volume and by PET maximum SUV. Although a correlation was observed, it did not reach statistical significance. Squamous histology responded faster by both relative CT volume and PET maximum SUV value after SBRT. Additional patient data is needed to correlate PET SUV response to CT volume reduction after SBRT.