CT- and MRI-based gross target volume comparison in vestibular schwannomas

Abstract

Aim

This study represents an enumeration and comparison of gross target volumes (GTV) as delineated independently on contrast-enhanced computed tomography (CT) and T1 and T2 weighted magnetic resonance imaging (MRI) in vestibular schwannomas (VS).

Background

Multiple imaging in radiotherapy improves target localization.

Methods and materials

42 patients of VS were considered for this prospective study with one patient showing bilateral tumor. The GTV was delineated separately on CT and MRI. Difference in volumes were estimated individually for all the 43 lesions and similarity was studied between CT and T1 and T2 weighted MRI.

Results

The male to female ratio for VS was found to be 1:1.3. The tumor was right sided in 34.9% and left sided in 65.1%. Tumor volumes (TV) on CT image sets were ranging from 0.251[[ce:hsp sp="0.25"/]]cc to 27.27[[ce:hsp sp="0.25"/]]cc. The TV for CT, MRI T1 and T2 weighted were 5.15[[ce:hsp sp="0.25"/]]±[[ce:hsp sp="0.25"/]]5.2[[ce:hsp sp="0.25"/]]cc, 5.8[[ce:hsp sp="0.25"/]]±[[ce:hsp sp="0.25"/]]6.23[[ce:hsp sp="0.25"/]]cc, and 5.9[[ce:hsp sp="0.25"/]]±[[ce:hsp sp="0.25"/]]6.13[[ce:hsp sp="0.25"/]]cc, respectively. Compared to MRI, CT underestimated the volumes. The mean dice coefficient between CT versus T1 and CT versus T2 was estimated to be 68.85[[ce:hsp sp="0.25"/]]±[[ce:hsp sp="0.25"/]]18.3 and 66.68[[ce:hsp sp="0.25"/]]±[[ce:hsp sp="0.25"/]]20.3, respectively. The percentage of volume difference between CT and MRI (%VD: mean[[ce:hsp sp="0.25"/]]±[[ce:hsp sp="0.25"/]]SD for T1; 28.84[[ce:hsp sp="0.25"/]]±[[ce:hsp sp="0.25"/]]15.0, T2; 35.74[[ce:hsp sp="0.25"/]]±[[ce:hsp sp="0.25"/]]16.3) and volume error (%VE: T1; 18.77[[ce:hsp sp="0.25"/]]±[[ce:hsp sp="0.25"/]]10.1, T2; 23.17[[ce:hsp sp="0.25"/]]±[[ce:hsp sp="0.25"/]]13.93) were found to be significant, taking the CT volumes as the baseline.

Conclusions

MRI with multiple sequences should be incorporated for tumor volume delineation and they provide a clear boundary between the tumor and normal tissue with critical structures nearby.