Evaluation of dual-energy CT virtual monoenergetic imaging for target delineation in rectal cancer radiotherapy.
prospective_cohort · Level II
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- Also identified by DOI 10.1016/j.radonc.2026.111488.
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Abstract
To evaluate the image quality of dual-energy CT (DECT) virtual monoenergetic imaging (VMI) in rectal cancer and to investigate its value for gross tumor volume (GTV) delineation in radiotherapy. Twenty-nine patients with rectal cancer receiving neoadjuvant chemoradiotherapy were prospectively enrolled. Each patient underwent contrast-enhanced DECT and 3.0 T MRI on the same day. Lesion contrast (LC), contrast-to-noise ratio (CNR), and signal-to-noise ratio (SNR) were assessed for VMI from 40-200 keV and synthetic 120 kVp CT (S<sub>120kVp</sub>), with the optimal monoenergetic image (VMI<sub>Eopt</sub>) determined accordingly. Three radiation oncologists independently assessed VMI<sub>Eopt</sub>, S<sub>120kVp</sub>, and T2WI-MRI for overall image quality and tumor delineation, and delineated GTVs. T2WI-MRI served as the reference. Dice similarity coefficient (DSC) was used to compare delineation performance, with further analysis of interobserver agreement and cranial-caudal margin identification. Venous-phase 40 keV VMI (VMI<sub>Eopt</sub>) showed significantly higher LC, CNR, and SNR than S<sub>120kVp</sub> (p < 0.0001). Subjective scores of VMI<sub>Eopt</sub> were comparable with MRI for both overall image quality (p = 0.040) and tumor delineation (p = 0.449). The concordance between VMI<sub>Eopt</sub>- and MRI-defined GTVs was significantly higher than that between S<sub>120kVp</sub>- and MRI-defined GTVs (mean DSC: 0.83 ± 0.04 vs 0.67 ± 0.10, p < 0.0001). In patients with high registration accuracy, the DSC for the VMI<sub>Eopt</sub>-MRI comparison further improved to 0.86 ± 0.01. Interobserver agreement was superior for VMI<sub>Eopt</sub> compared with S<sub>120kVp</sub> (0.82 ± 0.05 vs 0.76 ± 0.07, p < 0.001). Cranial and caudal margin errors were also significantly reduced when using VMI<sub>Eopt</sub> compared to S<sub>120kVp</sub>. Venous-phase 40 keV DECT VMI demonstrated objectively and subjectively superior image quality compared with S<sub>120kVp</sub>, significantly improving GTV delineation accuracy, interobserver consistency, and cranial-caudal margin identification. It may serve as a reliable imaging tool to balance tumor control and normal tissue sparing in rectal cancer radiotherapy.