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

Abstract

Previously, we showed that a CT window and level setting of 1,600 and -300 Hounsfield units, respectively, and autocontouring using an 18 F-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 18 F-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 (GTV CT ) was contoured manually using only CT information. The second set (GTV Auto ) was autocontoured using a 50% intensity level for 18 F-FDG PET images. The third set (GTV Manual ) was manually contoured using a visual method on PET images. The other 4 sets combined CT and 18 F-FDG PET images fused to one another to become composite volumes: GTV CT1Auto , GTV CT1Manual , GTV CT2Auto , and GTV CT-Manual . To quantitate the degree to which CT and 18 F-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 GTV CT , GTV Auto , GTV Manual , GTV CT1Auto , GTV CT1Manual , GTV CT-Auto , and GTV CT-Manual were 6. 96, 2.42, 4.37, 7.46, 10.17, 2.21, and 3.38 cm 3 , respectively. The median matching indexes of GTV CT versus GTV CT1Auto , GTV Auto versus GTV CT1Auto , GTV CT versus GTV CT1Manual , and GTV Manual versus GTV CT1Manual were 0.86, 0.65, 0.88, and 0.81, respectively. Compared with the maximum diameter on pathologic examination, the correlations of GTV CT , GTV Auto , GTV Manual , GTV CT1Auto , and GTV CT1Manual 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 18 F-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 18 F-FDG PET to check for any missed disease. It is well established that 18 F-FDG PET plays an important role in the staging of non-small cell lung cancer (NSCLC). Multiple studies have demonstrated the utility of PET for improving staging accuracy. In an overview of the available literature, 18 F-FDG PET was found to have a 79%-100% sensitivity and a 40%-90% specificity in diagnosing primary lung cancer (1).The conventional imaging modality for therapy planning in NSCLC is CT. Targeting of the gross tumor has been facilitated by the use of CT simulation, which allows for more accurate delineation of the tumor. Multimodality imaging combining functional and anatomic information such as PET has allowed for further refinement in the therapy planning process and has a significant impact on the planning target volume. However, much uncertainty exists regarding the most appropriate threshold cutoff that should be used to define a PET target volume in NSCLC therapy planning. There ar...

Impact of Tumor Size and Tracer Uptake Heterogeneity in 18F-FDG PET and CT Non–Small Cell Lung Cancer Tumor Delineation

“…On the other hand, we found differences between CT and PET volumes similar to those found by Wu et al in their subsequent study (13). CT volumes were significantly larger than PET-based volumes in both studies, despite the differences in tumor sizes considered.…”

“…Using morphologic imaging and manual delineation, we saw a large overestimation of tumor volume as previously described by several authors (13). Using a fixed threshold of 50% as recommended by Wu et al (11), the estimation of the maximum tumor diameter on PET images was not correct.…”

“…This conclusion was reached by comparing the results obtained using a range of different fixed thresholds (from 20% to 55%), although only nonstatistically significant differences were found with the other tested values. The same authors subsequently showed that such a threshold was less appropriate than manual delineation, which led to incorrect delineation in some cases (13). Manual contouring is far from ideal, as it suffers from large intra-and interobserver variability (14) and is also a tedious and time-consuming procedure, especially in 3 dimensions.…”

Large Decreases in Standardized Uptake Values After Definitive Radiation Are Associated with Better Survival of Patients with Locally Advanced Non–Small Cell Lung Cancer

“…The uptake of the glucose analog 18 F-FDG by NSCLC tumor cells has been found to be useful for restaging at recurrence and for delineating radiotherapeutic targets (9)(10)(11). The standardized uptake value (SUV) in 18 F-FDG PET before initial curative treatment has also been shown by some (12,13), but not all (14), to be a prognostic factor for survival outcomes.…”

Delineation gross tumor volume based on positron emission tomography images by a numerical approximation method

“…Manual drawing contours of tumors was very easily applied [4,5], but it was time-consuming and susceptibility to the window level setting. Several studies [5][6][7][8][9][10][11][12][13][14] had tried to outline the GTV using the optimal threshold value (ThV) of the SUV on tumor's PET images.…”