What Is the Best Way to Contour Lung Tumors on PET Scans? Multiobserver Validation of a Gradient-Based Method Using a NSCLC Digital PET Phantom

Abstract

Purpose To evaluate the accuracy and consistency of a gradient-based PET segmentation method, GRADIENT, as compared to manual (MANUAL) and constant threshold (THRESHOLD) methods. Methods and Materials Contouring accuracy was evaluated with sphere phantoms and clinically realistic Monte Carlo PET phantoms of the thorax. The sphere phantoms were 10–37 mm in diameter and were acquired at 5 institutions emulating clinical conditions. One institution also acquired a sphere phantom with multiple source-to-background ratios (SBR) of 2:1, 5:1, 10:1, 20:1, and 70:1. One observer segmented (contoured) each sphere with GRADIENT and THRESHOLD from 25–50% at 5% increments. Subsequently, seven physicians segmented lessions (7–264ml) from 25 digital thorax phantoms using GRADIENT, THRESHOLD, and MANUAL. Results For spheres < 20 mm in diameter, GRADIENT was the most accurate with a mean absolute %error in diameter of 8.15% (10.2%SD) compared to 49.2% (51.1%SD) for 45% THRESHOLD (p < 0.005). For larger spheres the methods were statistically equivalent. For varying SBR, GRADIENT was the most accurate for spheres > 20 mm, (p < 0.065) and < 20 mm (p < 0.015). For digital thorax phantoms, GRADIENT was the most accurate, (p-value < 0.01), with a mean absolute %error in volume of 10.99% (11.9%SD) followed by 25% THRESHOLD at 17.5% (29.4%SD), and MANUAL, at 19.5% (17.2%SD). GRADIENT had the least systematic bias, 4 with a mean %error in volume of −0.05% (16.2%SD) compared with 25% THRESHOLD at - 2.1% (34.2%SD) and MANUAL at −16.3% (20.2%SD) (p-value < 0.01). Inter-observer variability was reduced using GRADIENT compared to both 25% THRESHOLD and MANUAL (p-value < 0.01, Levene's Test). Conclusion GRADIENT was the most accurate and consistent technique for target volume contouring. GRADIENT was also the most robust for varying imaging conditions. GRADIENT has the potential to play an important role for tumor delineation in radiation therapy planning and response assessment.

Metabolic tumour volume and total lesion glycolysis, measured using preoperative 18F–FDG PET/CT, predict the recurrence of endometrial cancer

“…There is currently no consensus regarding the optimal technique to measure MTV. 27 Discrepancies and variabilities in MTV in certain solid tumours are reported with various measurement techniques, including EC; however, MTV is a prognostic indicator regardless of the technique. [27][28][29] We introduced a threshold method using the arbitrary value of 2.5 because it is a commonly used standard for malignant lesions.…”

Repeatability of 18F-FLT PET in a Multicenter Study of Patients with High-Grade Glioma

“…Quantitative SUV analysis (body weight normalization) used volumes of interest (VOIs) defined in tumor and normal brain. Tumor VOIs were determined using isocontour segmentation (30% of the maximum tumor voxel) and a gradient edge detection approach (24). The isocontour VOIs were determined automatically after a spheric guiding volume was manually specified.…”

Hybrid positron emission tomography segmentation of heterogeneous lung tumors using 3D Slicer: improved GrowCut algorithm with threshold initialization

“…The methods range from simple to complex methods. 1,3,4 The segmentation methods include but are not limited to constant and adaptive threshold methods, [5][6][7][8][9] region growing methods, [10][11][12] gradient-based methods, [13][14][15] fuzzy models, [16][17][18] and Gaussian mixture modeling. 10,19 All these methods offer different compromises in terms of versatility and performance and compare well against manual segmentations by clinicians or the pathological measurements with varying rates of success.…”