CyberKnife radiosurgery for inoperable stage IA non-small cell lung cancer: 18F-fluorodeoxyglucose positron emission tomography/computed tomography serial tumor response assessment

Abstract

Objective. To report serial 18F-fluorodeoxyglucose (18F-FDG) positron emission tomography (PET)/computed tomography (CT) tumor response following CyberKnife radiosurgery for stage IA non-small cell lung cancer (NSCLC). Methods. Patients with biopsy-proven inoperable stage IA NSCLC were enrolled into this IRB-approved study. Targeting was based on 3-5 gold fiducial markers implanted in or near tumors. Gross tumor volumes (GTVs) were contoured using lung windows; margins were expanded by 5 mm to establish the planning treatment volumes (PTVs). Doses ranged from 42-60 Gy in 3 equal fractions. 18F-FDG PET/CT was performed prior to and at 3-6-month, 9-15 months and 18-24 months following treatment. The tumor maximum standardized uptake value (SUVmax) was recorded for each time point. Results. Twenty patients with an average maximum tumor diameter of 2.2 cm were treated over a 3-year period. A mean dose of 51 Gy was delivered to the PTV in 3 to 11 days (mean, 7 days). The 30-Gy isodose contour extended an average of 2 cm from the GTV. At a median follow-up of 43 months, the 2-year Kaplan-Meier overall survival estimate was 90% and the local control estimate was 95%. Mean tumor SUVmaxbefore treatment was 6.2 (range, 2.0 to 10.7). During early follow-up the mean tumor SUVmaxremained at 2.3 (range, 1.0 to 5.7), despite transient elevations in individual tumor SUVmaxlevels attributed to peritumoral radiation-induced pneumonitis visible on CT imaging. At 18-24 months the mean tumor SUVmaxfor controlled tumors was 2.0, with. a narrow range of values (range, 1.5 to 2.8). A single local failure was confirmed at 24 months in a patient with an elevated tumor SUVmaxof 8.4. Conclusion. Local control and survival following CyberKnife radiosurgery for stage IA NSCLC is exceptional. Early transient increases in tumor SUV maxare likely related to radiation-induced pneumonitis. Tumor SUVmaxvalues return to background levels at 18-24 months, enhancing 18F-FDG PET/CT detection of local failure. The value of 18F-FDG PET/CT imaging for surveillance following lung SBRT deserves further study. © 2010 Vahdat et al; licensee BioMed Central Ltd.