PET CT Thresholds for Radiotherapy Target Definition in Non-Small-Cell Lung Cancer: How Close are we to the Pathologic Findings?

Kailiang Wu, Yee C. Ung*, Jennifer Hornby, Marc Freeman, David Hwang, Ming S. Tsao, Max Dahele, Gail Darling, Donna E. Maziak, Romeo Tirona, Kathy Mah, C. Shun Wong

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review


Purpose: Optimal target delineation threshold values for positron emission tomography (PET) and computed tomography (CT) radiotherapy planning is controversial. In this present study, different PET CT threshold values were used for target delineation and then compared pathologically. Methods and Materials: A total of 31 non-small-cell lung cancer patients underwent PET CT before surgery. The maximal diameter (MD) of the pathologic primary tumor was obtained. The CT-based gross tumor volumes (GTVCT) were delineated for CT window-level thresholds at 1,600 and -300 Hounsfield units (HU) (GTVCT1); 1,600 and -400 (GTVCT2); 1,600 and -450 HU (GTVCT3); 1,600 and -600 HU (GTVCT4); 1,200 and -700 HU (GTVCT5); 900 and -450 HU (GTVCT6); and 700 and -450 HU (GTVCT7). The PET-based GTVs (GTVPET) were autocontoured at 20% (GTV20), 30% (GTV30), 40% (GTV40), 45% (GTV45), 50% (GTV50), and 55% (GTV55) of the maximal intensity level. The MD of each image-based GTV in three-dimensional orientation was determined. The MD of the GTVPET and GTVCT were compared with the pathologically determined MD. Results: The median MD of the GTVCT changed from 2.89 (GTVCT2) to 4.46 (GTVCT7) as the CT thresholds were varied. The correlation coefficient of the GTVCT compared with the pathologically determined MD ranged from 0.76 to 0.87. The correlation coefficient of the GTVCT1 was the best (r = 0.87). The median MD of GTVPET changed from 5.72cm to 2.67cm as the PET thresholds increased. The correlation coefficient of the GTVPET compared with the pathologic finding ranged from 0.51 to 0.77. The correlation coefficient of GTV50 was the best (r = 0.77). Conclusion: Compared with the MD of GTVPET, the MD of GTVCT had better correlation with the pathologic MD. The GTVCT1 and GTV50 had the best correlation with the pathologic results.

Original languageEnglish
Pages (from-to)699-706
Number of pages8
JournalInternational Journal of Radiation Oncology Biology Physics
Issue number3
Publication statusPublished - 2010

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