Consensus report on the radiological management of patients with gastrointestinal stromal tumours (GIST): recommendations of the German GIST Imaging Working Group

Abstract

The aim was to reach consensus in imaging for staging and follow-up as well as for therapy response assessment in patients with gastrointestinal stromal tumours (GIST). The German GIST Imaging Working Group was formed by 9 radiologists engaged in assessing patients with GIST treated with targeted therapy. The following topics were discussed: indication and optimal acquisition techniques of computed tomography (CT), magnetic resonance imaging (MRI) and positron emission tomography (PET)/CT; tumour response assessment considering response criteria and measurement techniques on CT, MRI and PET/CT; result interpretation; staging interval and pitfalls. Contrast-enhanced CT is the standard method for GIST imaging. MRI is the method of choice in case of liver-specific questions or contraindications to CT. PET/CT should be used for early response assessment or inconclusive results on morphologic imaging. All imaging techniques should be standardized allowing a reliable response assessment. Response has to be assessed with respect to lesion size, lesion density and appearance of new lesions. A critical issue is pseudoprogression due to myxoid degeneration or intratumoural haemorrhage. The management of patients with GIST receiving a targeted therapy requires a standardized algorithm for imaging and an appropriate response assessment with respect to changes in lesion size and density.

Comparison of Choi criteria and Response Evaluation Criteria in Solid Tumors (RECIST) for intrahepatic cholangiocarcinoma treated with glass-microspheres Yttrium-90 selective internal radiation therapy (SIRT)

“…Regarding the density measurement, we chose a widespread, simple and reproducible method by performing an average of the densities in a ROI encompassing the whole lesion [18]. Finally, as a relatively hypodense lesion at baseline, measurements of density variations in ICC may be less reliable than in hypervascular lesions such as gastrointestinal stromal tumors or hepatocellular carcinoma, since a small absolute decrease of density may lead to a high relative variation.…”

“…Finally, as a relatively hypodense lesion at baseline, measurements of density variations in ICC may be less reliable than in hypervascular lesions such as gastrointestinal stromal tumors or hepatocellular carcinoma, since a small absolute decrease of density may lead to a high relative variation. This is why we followed the recommendation of the German GIST imaging working group and added a minimal 10 Hounsfield Units absolute decrease to the 15% relative decrease in density to validate a PR [18].…”

“…For each target lesion, the maximum diameter, and tumor density were measured. Tumor density was evaluated at the portal phase by selecting a polygonal region of interest encompassing the entire target lesions on the slice of the measurement of the largest diameter [18] (Figure 2). Although ICC may enhance on delayed acquisitions, the portal phase was used in agreement with the original method described by Choi and al.…”

“…A decrease in density ≥ 15% was accepted as a criterion of partial response according to Choi only if the absolute density change would account for at least 10 Hounsfield Units [18]. In case of multiple 90 Y SIRT injections, the response was evaluated on the treated lesions at the time of evaluation.…”

Radiological Monitoring of the Treatment of Solid Tumors in Practice

“…Positron emission tomography (PET) with FDG is suitable in this regard for determining early treatment response since the glycometabolism of GIST tumors decreases after only 24 hours in the case of treatment response. Since FDG-PET is only available on a limited basis economically and practically, H. Choi correlated the change in density in contrast-enhanced CT in the portal-venous phase with the response criteria for PET and thus defined relatively easy to use criteria that make it possible to evaluate response primarily on the basis of the change in density in CT. For the practical implementation of diagnostics and follow-up, a group of German experts recently published a consensus recommendation for the "CHOI criteria" since they have found increasing acceptance in practice [7,30].…”