Impact of Integrated PET/CT on Variability of Target Volume Delineation in Rectal Cancer

Abstract

Several studies have demonstrated substantial variability among individual radiation oncologists in defining target volumes using computed tomography (CT). The objective of this study was to determine the impact of combined positron emission tomography and computed tomography (PET/CT) on inter-observer variability of target volume delineation in rectal cancer. We also compared the relative concordance of two PET imaging tracers, The use of FDG and FLT did not appear to be different from this perspective.

Biological image-guided radiotherapy in rectal cancer: Is there a role for FMISO or FLT, next to FDG?

“…The delineation is then performed by constructing for instance a 50% isocontour of the maximum SUV [29]. Other authors used a visual interpretation of the PET signal, starting with a fixed window/level according to a gray intensity scale and allowing adjustment of this scale according to the judgement of the observer [30]. This method can obviously change the size of the TV depending on the applied PET window/level and can explain the relatively large PET TVs obtained in this study compared to CT.…”

“…These findings confirm the results of Patel and al. evaluated the impact of combined FDG and FLT-PET/CT on inter-observer variability of target volume delineation in rectal cancer [30] against CT. In 5 of the 6 patients enrolled, the FDG and FLT TV was larger than the CT TV.…”

Comparison of Tumor Volumes Derived from Glucose Metabolic Rate Maps and SUV Maps in Dynamic 18F-FDG PET

“…It is expected that the combined use of CT and the functional information from 18 F-FDG PET will lead to improved tumor delineation (1)(2)(3)(4)(5)(6)(7)(8)(9). However, until now, tumor delineation using PET has been based on static images of 18 F-FDG uptake obtained at a fixed time after injection.…”

Biological Image-Guided Radiotherapy in Rectal Cancer: Challenges and Pitfalls

“…Various imaging modalities that give anatomic and functional information have been tested for definition of the tumor volume (TV) for various tumor sites (4)(5)(6)(7)(8). Computed tomography (CT) generally has a poor soft-tissue contrast, which makes it less reliable for accurate delineation of the TV (6,9). Nonetheless, CT is needed for planning and subsequent verification of radiation treatment because CT provides electron densities.…”

“…This can be achieved with three-dimensional (3D) conformal and intensity-modulated RT, which allow optimal dose distributions but require a precise definition and an accurate location of the target volume. Various imaging modalities that give anatomic and functional information have been tested for definition of the tumor volume (TV) for various tumor sites (4)(5)(6)(7)(8). Computed tomography (CT) generally has a poor soft-tissue contrast, which makes it less reliable for accurate delineation of the TV (6,9).…”