# PET/CT and MR Improve Interobserver Agreement in Primary Tumor Determination for Radiotherapy in Esophageal Squamous Cell Cancer

## TL;DR

Using PET/CT and MR imaging improves agreement among doctors when defining the primary tumor for radiotherapy in esophageal cancer.

## Contribution

This study shows that PET/CT and fused MR imaging increase interobserver agreement in tumor delineation for ESCC radiotherapy.

## Key findings

- PET/CT with fused MR had the highest conformity index (0.71) for tumor agreement.
- PET/CT alone improved agreement compared to CT alone (p = 0.003).
- Fused MR with PET/CT outperformed PET/CT alone (p = 0.002).

## Abstract

Background/Objectives: The aim of the study was to evaluate interobserver variability in the determination of the primary tumor for radiotherapy treatment planning in esophageal squamous cell carcinoma (ESCC). Methods: Sixteen patients with locally advanced ESCC were included in the analysis. In all patients positron emission tomography with computed tomography (PETC/CT) and magnetic resonance (MR) scans for radiotherapy planning were performed. Five experienced radiation oncologists delineated the primary tumor based on CT alone, MR alone, PET/CT, CT with fused MR and PET/CT with fused MR. Mean tumor volumes were calculated for each patient and imaging modality. The generalized conformity index (CIgen) was calculated to assess agreement in tumor determination. Results: The mean tumor volumes and CIgen for CT alone, MR alone, PET/CT, CT with fused MR and PET/CT with fused MR were 33.1 cm3, 30.2 cm3, 38.1 cm3, 31.9 cm3, 36.2 cm3 and 0.59, 0.64, 0.66, 0.63, 0.71, respectively. CIgen was significantly higher using PET/CT with fused MR compared to CT (p < 0.001) and PET/CT (p = 0.002) and using PET/CT compared to CT (alone) (p = 0.003). Conclusions: Our study showed higher agreement in primary tumor determination in ESCC using PET/CT compared to CT alone. Higher agreement was also found using PET/CT with fused MR compared to CT alone and PET/CT.