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Primary tumor volume measured by FDG PET and CT in nasopharyngeal carcinoma
Guang-Uei Hung1, Iuan-Sheng Wu, Hong-Shen Lee
1Department of Nuclear Medicine, Chang-Bing Show Chwan Memorial Hospital, Changhua, Taiwan.
Background:
The prognostic value of CT-derived primary tumor volume in patients with nasopharyngeal carcinoma (NPC) has been demonstrated in our previous serial studies. The purpose of the present study is to compare the primary tumor volume measured by FDG PET and traditional CT in NPC, and to ascertain their prognostic value.
Materials And Methods:
From 2007 to 2008, 32 patients with newly diagnosed NPC were prospectively studied. All patients underwent a CT scan, followed by a FDG PET/CT scan. CT-derived primary tumor volume (VolumeCT) was measured using the summation-of-area technique. PET-volume was measured using 3 methods: delineating the contour of tumor with the threshold of standardized uptake value (SUV) ≧2.5 (Volume2.5), ≧40% of maximal SUV (Volume40%), and ≧50% of maximal SUV (Volume50%). The primary tumor volumes derived from the 4 methods, VolumeCT, Volume2.5, Volume40%, and Volume50%, were compared. Univariate Cox regression was used to identify the above parameters as prognosticators.
Results:
The volumes derived from the VolumeCT, Volume2.5, Volume40%, and Volume50% methods were 16.48 ± 12.46 cm(3), 25.87 ± 16.96 cm(3), 13.66 ± 6.90 cm(3), and 8.25 ± 4.52 cm(3), respectively. There was decent correlation between VolumeCT and Volume2.5 (r = 0.64, P = 0.0001), and Volume2.5 was systemically larger than VolumeCT. No significant difference was noted between VolumeCT and Volume40% (P = 0.24), but the correlation was poor (r = 0.15, P = 0.39). For VolumeCT and Volume50%, the difference was significant (P = 0.0006) and the correlation was poor (r = 0.23, P = 0.20). Larger tumor volumes presented as VolumeCT, Volume2.5, and Volume50% were associated with shorter overall survival.
Conclusion:
PET-derived primary tumor volumes are substantially different from CT-derived tumor volumes, only decent correlation is noted between VolumeCT and Volume2.5. Volume2.5 and Volume50% seem to be reasonable alternatives for VolumeCT in predicting the patient outcomes.
