Quantification and minimization of uncertainties of internal target volume for stereotactic body radiation therapy of lung cancer.
PURPOSE: To quantify uncertainties in delineating an internal target volume (ITV) and to understand how these uncertainties may be individually minimized for stereotactic body radiation therapy (SBRT) of early stage non-small cell lung cancer (NSCLC). METHODS AND MATERIALS: Twenty patients with NSCLC who were undergoing SBRT were imaged with free-breathing 3-dimensional computed tomography (3DCT) and 10-phase 4-dimensional CT (4DCT) for delineating gross tumor volume (GTV)(3D) and ITV(10Phase) (ITV3). The maximum intensity projection (MIP) CT was also calculated from 10-phase 4DCT for contouring ITV(MIP) (ITV1). Then, ITV(COMB) (ITV2), ITV(10Phase+GTV3D) (ITV4), and ITV(10Phase+ITVCOMB) (ITV5) were generated by combining ITV(MIP) and GTV(3D), ITV(10phase) and GTV(3D), and ITV(10phase) and ITV(COMB), respectively. All 6 volumes (GTV(3D) and ITV1 to ITV5) were delineated in the same lung window by the same radiation oncologist. The percentage of volume difference (PVD) between any 2 different volumes was determined and was correlated to effective tumor diameter (ETD), tumor motion ranges, R(3D), and the amplitude variability of the recorded breathing signal (v) to assess their volume variations. RESULTS: The mean (range) tumor motion (R(SI), R(AP), R(ML), and R(3D)) and breathing variability (v) were 7.6 mm (2-18 mm), 4.0 mm (2-8 mm), 3.3 mm (0-7.5 mm), 9.9 mm (4.1-18.7 mm), and 0.17 (0.07-0.37), respectively. The trend of volume variation was GTV(3D)
Ge, H; Cai, J; Kelsey, CR; Yin, F-F
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