Autocontouring and Manual Contouring: Which Is the Better Method for Target Delineation Using 18F-FDG PET/CT in Non–Small Cell Lung Cancer?

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Abstract
Previously, we showed that a CT window and level setting of 1,600 and –300 Hounsfield units, respectively, and autocontouring using an 18F-FDG PET 50% intensity level correlated best with pathologic results. The aim of this study was to compare this autocontouring with manual contouring, to determine which method is better. Methods: Seventeen patients with non–small cell lung cancer underwent 18F-FDG PET/CT before surgery. The maximum diameter on pathologic examination was determined. Seven sets of gross tumor volumes (GTVs) were defined. The first set (GTVCT) was contoured manually using only CT information. The second set (GTVAuto) was autocontoured using a 50% intensity level for 18F-FDG PET images. The third set (GTVManual) was manually contoured using a visual method on PET images. The other 4 sets combined CT and 18F-FDG PET images fused to one another to become composite volumes: GTVCT+Auto, GTVCT+Manual, GTVCT−Auto, and GTVCT–Manual. To quantitate the degree to which CT and 18F-FDG PET defined the same region of interest, a matching index was calculated for each case. The maximum diameter of GTV was compared with the maximum diameter on pathologic examination. Results: The median GTVCT, GTVAuto, GTVManual, GTVCT+Auto, GTVCT+Manual, GTVCT–Auto, and GTVCT–Manual were 6.96, 2.42, 4.37, 7.46, 10.17, 2.21, and 3.38 cm3, respectively. The median matching indexes of GTVCT versus GTVCT+Auto, GTVAuto versus GTVCT+Auto, GTVCT versus GTVCT+Manual, and GTVManual versus GTVCT+Manual were 0.86, 0.65, 0.88, and 0.81, respectively. Compared with the maximum diameter on pathologic examination, the correlations of GTVCT, GTVAuto, GTVManual, GTVCT+Auto, and GTVCT+Manual were 0.87, 0.83, 0.93, 0.86, and 0.94, respectively. Conclusion: The matching index was higher for manual contouring than for autocontouring using a 50% intensity level on 18F-FDG PET images. When using a 50% intensity level to contour the target of non–small cell lung cancer, one should also consider using manual contouring of 18F-FDG PET to check for any missed disease.

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