The effect of replacing cochlea contour with inner ear contour on cochlea dose-volume calculations in conventional 2-dimensional and conformal 3-dimensional radiotherapy of brain

Abstract

Background: Sensorineural hearing loss is a radiotherapy complication in patients with brain tumors. The auditory system of patients with brain tumors often is placed inside of radiation field, and receives a significant amount of radiation dose resulting in hearing loss. The purpose of this study was to compare the calculated dose by contouring cochlea or inner ear in two techniques of 3-dimensional (3D) conformal radiotherapy and 2-dimensional (2D) conventional radiotherapy in patients with brain tumors. Methods: In this cross-sectional case study, computed tomography (CT) scans of 43 patients (23 men and 20 woman) were used. Patients were treated for brain tumor at the radiotherapy unit of Milad hospital, Isfahan, Iran, in 2016. Contouring of cochlea and inner ear was done on the patients’ images by a radiation oncologist, using TiGRT treatment planning system. Calculated dose volume histograms (DVHs) were compared for 2-and 3-dimensional radiotherapy techniques. Findings: For the cochlea and inner ear, the mean dose was 2624 ± 338.7 and 2718.3 ± 341.3 centigray (cGy) in 2-dimensional, and 2507 ± 294.6 and 2581 ± 295.6, in 3-dimensional radiotherapy techniques, respectively. The mean dose of inner ear and cochlea in 3-dimensional technique was 5.3 and 4.6 percent lower than 2-dimensional technique, respectively. There was no significant difference between the dose of cochlea and inner ear in 2-dimensional (P = 0.846) and 3-dimensional (P = 0.859) radiotherapy techniques. Conclusion: As dosimetric parameters of the auditory system showed no statistical difference between the dose of cochlea and inner ear in none of 2-and 3-dimensional radiotherapy techniques, in treatment planning of these two techniques, contour of cochlea can be replaced by inner ear contour. © 2018, Isfahan University of Medical Sciences(IUMS). All rights reserved.