ESTRO 2024 - Abstract Book

S2225

Clinical - Upper GI

ESTRO 2024

MRI provides superior soft tissue contrast in the GI tract and is therefore hypothesised to aid TVD for gastric RT. 10

We undertook a study to assess the qualitative and quantitative IOV in gastric TVD using CT and the addition of MRI to determine the role of MRI in gastric RT and inform future trial TVD protocols.

Material/Methods:

Diagnostic CT scans of two patients with gastric/type III gastro-oesophageal junction adenocarcinoma were anonymised and imported into local TPS in lieu of a CT planning scan. Respective MRI images (undertaken to evaluate liver lesions) were provided for reference, but not co-registered. Observers (consultant oesophagogastric [OG] clinical oncologists/ post FRCR fellows) were randomised to outline case 1 or case 2 and were provided imaging reports, a detailed instruction manual, imaging atlases and asked to delineate in 2 stages: Stage 1) Delineate GTVp, GTVn (involved nodes) and CTVstomach (whole stomach including pylorus, excluding un-involved GOJ) using CT alone. Stage 2) Delineate the same volumes on CT with addition of MRI for reference (T2, diffusion weighted [DWI], and contrast enhanced sequences). TVD was performed individually and observers were blinded to each others volumes.

After each stage, observers completed a questionnaire exploring ease of delineation, time taken and perceived areas of difficulty.

A single gold standard reference volume (RV) was created at a consensus meeting of 2 OG oncologists and 2 specialist OG radiologists, the latter having previously independently delineated the two cases.

All data was anonymised and exported to CERR (Computational Environment for Radiological Research) for analysis. Observer volumes were compared against the respective RV. JCI (Jaccard conformity index) was calculated.

Results:

Nineteen observers undertook the TVD exercise; Case 1 n=11, Case 2 n=10 (2 observers delineated both cases).

Eighty-four RT structures were analysed for conformity against the RV (see figure).