The impact of MRI sequence on tumour staging and gross tumour volume delineation in squamous cell carcinoma of the anal canal

Davide Prezzi,Andrew Gaya,Ramin Mandegaran,Vicky Goh,Robert Glynne-Jones,Sofia Gourtsoyianni,Katarzyna Owczarczyk

doi:10.1007/s00330-017-5133-0

Abstract

ObjectivesTo compare maximum tumour diameter (MTD) and gross tumour volume (GTV) measurements between T2-weighted (T2-w) and diffusion-weighted (DWI) MRI in squamous cell carcinoma of the anal canal (SCCA) and assess sequence impact on tumour (T) staging. Second, to evaluate interobserver agreement and reader delineation confidence.MethodsThe staging MRI scans of 45 SCCA patients (25 females) were assessed retrospectively by two independent radiologists (0 and 5 years’ experience of anal cancer MRI). MTD and GTV were delineated on both T2-w and high-b-value DWI images and compared between sequences; T staging was derived from MTD. Interobserver agreement was assessed and delineation confidence scored (1 to 5) by each observer.ResultsGTV and MTD were significantly and systematically lower on DWI versus T2-w sequences by 14.80%/9.98% (MTD) and 29.70%/12.25% (GTV) for each reader, respectively, causing T staging discordances in approximately a quarter of cases. Bland-Altman limits of agreement were narrower and intraclass correlation coefficients higher for DWI. Delineation confidence was greater on DWI: 40/42 cases were scored confidently (4 or 5) by each reader, respectively, versus 31/36 cases based on T2-w images.ConclusionsSequence selection affects SCCA measurements and T stage. DWI yields higher interobserver agreement and greater tumour delineation confidence.Key Points• MTD and GTV measurements are significantly lower on DWI than on T2-w MRI.• Such differences cause T staging discordances in up to a quarter of cases.• DWI results in higher agreement between inexperienced and experienced observers.• DWI offers greater tumour delineation confidence to inexperienced readers.

Highlights

The incidence of squamous-cell carcinoma of the anus (SCCA), commonly referred to as anal cancer, has increased steadily over the past 4 decades in the Western world [1, 2]
Delineation confidence was greater on Diffusion-weighted imaging (DWI): 40/42 cases were scored confidently (4 or 5) by each reader, respectively, versus 31/36 cases based on T2-w images
maximum tumour diameter (MTD) and gross tumour volume (GTV) measurements are significantly lower on DWI than on T2-w Magnetic resonance imaging (MRI)

Summary

Introduction

The incidence of squamous-cell carcinoma of the anus (SCCA), commonly referred to as anal cancer, has increased steadily over the past 4 decades in the Western world [1, 2]. High-resolution T2-weighted (T2-w) sequences, obtained in the appropriate planes, provide detailed anatomical depiction of the anorectal region thanks to optimal soft-tissue contrast [5,6,7,8] and are in principle best suited for accurate target volume delineation. Diffusion-weighted imaging (DWI) is routinely included in body MRI protocols in most European oncological imaging centres: it has been shown to aid the diagnosis and response assessment of a variety of malignancies [9,10,11,12,13] and to allow the detection of small tumours in the pelvis [14]. Hypercellular tumours restrict water diffusion in the extracellular-extravascular space and typically stand out as bright lesions on a ‘dark’ background of suppressed signal on high b-value sequences, facilitating detection and delineation. Anal cancers typically appear restricted on DWI [15]

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