RESUMO
Purpose To estimate and discuss the feasibility of the threshold value of the internal tumor volume (ITV) of lung cancer based on the standardized uptake value (SUV) of the background.Materials and Methods The phantom was designed with 3 vacuous models fixed at the bottom of a barrel. The 3 vacuous models were filled with18F-FDG (55.0 kBq/ml) which represented a tumor and the barrel was filled with18F-FDG (5.9 kBq/ml), which represented the background of the lung. The barrel moved sinusoidally with distances of 10.9 mm, 21.8 mm, and 43.7 mm to simulate breathing, and then the phantom 2D PET/CT data were acquired. The SUV in the background was recorded as ±SD, and+3SD was regarded as threshold value to obtain the measured ITVs. The Dice similarity coefficient (DSC) and volume recovery coefficient (VRC) were used to evaluate the accuracy of the ITVs measured by seven methods, including that by SUV 2.5, 35% SUVmax, 41% SUVmax, a×mSUV70+b×, 0.42×(SUVmax+) and Riegel et al. computed threshold value followed the gross tumor volume, tumor-to-nontumor ratio and motion extent.Results Nine ITVs of three lung cancer models were 134.3 ml, 166.1 ml, 223.5 ml, 86.6 ml, 108.5 ml, 150.7 ml, 32.3 ml, 43.8 ml and 63.6 ml, respectively. The ITV measured by Riegel et al. showed no difference with the real ITV (t=-0.48,P>0.05). The ITVs measured by the other six methods were significantly different from the real ITVs (t=-5.11-2.76,P0.05). Moreover, they surpassed the results of the other five methods.Conclusion The threshold value (+3SD) of the SUV determined by the background has potential value in the description of the ITV of lung cancer, so as to provide reference for radiotherapy.
RESUMO
OBJECTIVE: A scheme, named SUV_Shape, for the gross tumor volume (GTV) delineation on positron emission tomography (PET) images was designed by a numerical approximation method, and evaluated during this study. METHODS: Twenty-one vacuous plastic balls of different shapes and sizes, their volumes ranged from 0.56 to 179.50 mL and were confirmed by a BL610 balance (Sartorius, Canada), consisted of four group models. Every group model was filled with a specific activity [18F]-FDG solution (55.1, 38.2, 23.7, and 36.3 kBq/mL) represented tumor, and fixed at the bottom of a barrel which was filled with unlike [18F]-FDG solution (5.4, 6.8, 8.1, and 4.0 kBq/mL, correspondingly) represented the background. The PET data of them were acquired by two-dimensional and three-dimensional mode in a PET/CT scanner (Discovery ST8, GE Healthcare, USA). The volume of each ball was measured by SUV_Shape, and the BL610 balance, labeled as GTVs and GTVt, respectively. Five rabbits implanted VX2 squamous carcinomas were acquired by [18F]-FDG PET/CT. These rabbits were mercy killed within 24 h after PET/CT acquisition. VX2 tumors were surgically removed, and their volumes were measured by SUV_Shape, and caliper, labeled as GTVs and GTVt. The Spearman's ρ between GTVs and GTVt were done. RESULTS: The tumor-background ratios in four groups of phantom models were 10.3, 5.6, 2.9, and 9.0, respectively. The relationship between GTVt and GTVs for phantom models was significant (Spearman's ρ > 0.95, P < 0.01), regardless of the different acquisition modes. Twelve VX2 tumor nodes or masses were measured; their GTVt ranged from 0.11 to 29.26 mL. The relationship between GTVt and GTVs was significant (Spearman's ρ = 0.893, P < 0.01) for animal tumor models. CONCLUSIONS: The SUV_Shape scheme could delineate tumors based on their radiopharmaceutical-avid PET images.
