Volume Delineation in Cervical Cancer With T2 and Diffusion-weighted MRI: Agreement on Volumes Between Observers

Abstract

Aim: To delineate cervical cancer gross tumor volume (GTV) on T2-magnetic resonance imaging (MRI) and apparent diffusion coefficient (ADC) maps, assessing volumes and inter-observer agreement between two observers. Patients and Methods: A radiologist and a radiation oncologist delineated GTV on T2 (T2 GTV) and ADC (ADC GTV) sequences. Dice similarity index (DICE) and Bland-Altman analysis were used to estimated concordance. Results: Mean T2 GTV and ADC GTV volumes were 43.84±71.47 cc and 37.28±68.92 cc according to the radiologist, and 43.4±70.44 cc and 36.65±69.21 cc according to the radiation oncologist. ADC led to statistically significantly smaller volumes compared to T2. The mean DICE index was 0.86 for T2 GTV and 0.84 for ADC GTV. The Bland-Altman plots globally showed concordance. Conclusion: GTV delineation was smaller in the ADC maps compared to T2-MRI, reaching an almost perfect agreement between observers. Thanks to this acceptable variability, adding functional imaging might provide more information for tumor delineation, improving reproducibility for image-guided adaptive radiotherapy. Nowadays, the mainstay of treatment for locally advanced cervical cancer (LACC) includes external beam radiotherapy (EBRT), concomitant chemotherapy and brachytherapy. T2weighted magnetic resonance imaging (MRI) is the imaging modality to be preferred for careful and accurate primary staging of the tumor (1, 2). Despite the extensive use of MRI, recent studies reported significant uncertainties in T2-weighted MRI delineation, describing a poor interobserver variability in brachytherapy target volume, represented by conformity indices of 0.58-0.60 for gross tumor volume (GTV) at brachytherapy, and 0.39-0.79 (mostly between 0.70-0.79) for high-risk clinical target volume (3, 4). Considering this aspect and the possible advantages of improved diagnostic techniques in a dose-intensification strategy, in particular in patients with higher risk of local relapse, its integration with diffusion-weighted MRI (DWI) might improve tumor volume definition in addition to patient outcome. In this way, a recent study demonstrated the accuracy of the apparent diffusion coefficient (ADC) map obtained at 2 weeks during radiotherapy in allowing an early prediction of treatment response (5). DWI-MRI is considered an encouraging functional imaging mode in the definition of a biological target volume, thanks to its capability for detecting highly metabolic regions. DWI-MRI evaluates the random motion of water molecules, mostly present in the extracellular space: compared to normal tissue, in cervical cancer, as in other neoplasms, tumor is densely cellular, showing restricted diffusion. This distribution is quantitatively well measured by ADC. In DWI, cancer has an increased signal intensity, which results in a reduction of the corresponding ADC map. It is well established that both DWI techniques as well as ADC measurement improves cervical cancer clinical assessment, regarding both tumor and nodal status, and histology (6). Few studies hav...

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