GTV delineation in supraglottic laryngeal carcinoma: interobserver agreement of CT versus CT-MR delineation

Abstract

BackgroundGTV delineation is the first crucial step in radiotherapy and requires high accuracy, especially with the growing use of highly conformal and adaptive radiotherapy techniques. If GTV delineations of observers concord, they are considered to be of high accuracy.The aim of the study is to determine the interobserver agreement for GTV delineations of supraglottic laryngeal carcinoma on CT and on CT combined with MR-images and to determine the effect of adding MR images to CT-based delineation on the delineated volume and the interobserver agreement.MethodsTwenty patients with biopsy proven T1-T4 supraglottic laryngeal cancer, treated with curative intent were included. For all patients a contrast enhanced planning CT and a 1.5-T MRI with gadolinium were acquired in the same head-and-shoulder mask for fixation as used during treatment. For MRI, a two element surface coil was used as a receiver coil. Three dedicated observers independently delineated the GTV on CT. After an interval of 2 weeks, a set of co-registered CT and MR-images was provided to delineate the GTV on CT. Common volumes (C) and encompassing volumes (E) were calculated and C/E ratios were determined for each pair of observers. The conformity index general (CIgen) was used to quantify the interobserver agreement. Results: In general, a large variation in interobserver agreement was found for CT (range: 0.29-0.77) as well as for CT-MR delineations (range: 0.17-0.80). The mean CIgen for CT (0.61) was larger compared to CT-MR (0.57) (p = 0.032). Mean GTV volume delineated on CT-MR (6.6 cm3) was larger compared to CT (5.6 cm3) (p = 0.002).ConclusionDelineation on CT with co-registered MR-images resulted in a larger mean GTV volume and in a decrease in interobserver agreement compared to CT only delineation for supraglottic laryngeal carcinoma.Electronic supplementary materialThe online version of this article (doi:10.1186/s13014-014-0321-4) contains supplementary material, which is available to authorized users.

Validated guidelines for tumor delineation on magnetic resonance imaging for laryngeal and hypopharyngeal cancer

“…Target delineation, however, is one of the largest sources of uncertainty in head-and-neck cancer radiotherapy [1]. Even with the introduction of new imaging techniques the interobserver variability remains relatively large [2][3][4][5]. For an accurate definition of the target volume, validation of gross tumor volume (GTV) delineation is fundamental.…”

“…Several studies [2,3,5,[9][10][11] have been performed, using various imaging modalities, to determine the agreement among observers when delineating the GTV in head-and-neck cancer. Studies in which CT was compared to MRI demonstrated contradictory results concerning the added value of MRI based on the inter-observer variation [3,4,11]. However, a considerable number of studies reported an increased visualization of boundaries between different tissues and increased soft tissue contrast with MRI compared to CT [3,4,[9][10][11][12].…”

“…Studies in which CT was compared to MRI demonstrated contradictory results concerning the added value of MRI based on the inter-observer variation [3,4,11]. However, a considerable number of studies reported an increased visualization of boundaries between different tissues and increased soft tissue contrast with MRI compared to CT [3,4,[9][10][11][12]. Thus, in head-and-neck cancer, especially in the laryngeal region, there is no consensus on the added value of MRI for improving agreement between observers.…”

“…However, there is agreement that visualization of soft tissue structures is better on MRI. A possible explanation for this contradiction is the increased visibility of anatomical details on MR images in combination with the lack of clear interpretation and delineation guidelines, what might result in an increased variability [4]. According to a study performed by Rasch et al [3], the use of guidelines for delineation might be of value.…”

Technical Note: Diffusion‐weighted MRI with minimal distortion in head‐and‐neck radiotherapy using a turbo spin echo acquisition method

“…Target volumes determined on CT and MRI are largely overestimated as shown in pathological validation studies. 1,2 Diffusion-weighted (DW) MRI is a functional imaging technique that provides information on the local mobility of water in tissue. Dense tissues with an increased cellularity, such as glandular and nodal structures or tumors, will restrict the motion of water and show high contrast with surrounding tissue.…”