Abstract
ObjectiveTo 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).MethodsPatients 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.ResultsTwenty 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 SUVmax before treatment was 6.2 (range, 2.0 to 10.7). During early follow-up the mean tumor SUVmax remained at 2.3 (range, 1.0 to 5.7), despite transient elevations in individual tumor SUVmax levels attributed to peritumoral radiation-induced pneumonitis visible on CT imaging. At 18-24 months the mean tumor SUVmax for controlled tumors was 2.0, witha 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 SUVmax of 8.4.ConclusionLocal control and survival following CyberKnife radiosurgery for stage IA NSCLC is exceptional. Early transient increases in tumor SUVmax are 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.
Highlights
Stereotactic body radiation therapy (SBRT) is an accepted treatment for inoperable stage I non-small cell lung cancer (NSCLC) [1,2,3,4,5,6,7,8,9,10,11,12]
Proven clinical stage IA NSCLC were treated over a 3-year period extending from January 2005 to January 2008 (Table 1)
computed tomography (CT) imaging evidence of focal radiationinduced pneomonitis and fibrosis was consistently observed within the target volumes of our patients during follow-up as well [18,19]. 18F-FDG positron emission tomography (PET)/CT is the standard imaging tool for NSCLC at Georgetown University Hospital
Summary
Stereotactic body radiation therapy (SBRT) is an accepted treatment for inoperable stage I NSCLC [1,2,3,4,5,6,7,8,9,10,11,12]. Several techniques have been employed to treat these potentially mobile tumors with relatively tight margins (5-10 mm). This enhanced accuracy has facilitated the safe, swift delivery of extremely high radiation doses. As anticipated, such treatment has improved local control and overall survival rates relative to historical controls. A reliable noninvasive means of detecting early local failure following SBRT remains to be established
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