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

Introduction: Sensorineural hearing loss (SNHL) is one of the possible complications of radiotherapy treatment of 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 contouring and delivery dose to cochlea and inner ear in two techniques of 3D conformal radiotherapy (3DCRT) vs 2D conventional radiotherapy in patients with brain tumors Materials and Methods: This was a prospective study. Forty-three patients (23male and 20 female) who received radiotherapy for brain tumors in the radiation oncology department of Isfahan Milad Hospital during 2016 entered the study. Computerized tomography (CT) images of the patients were used for contouring of cochlea and inner ear by radiation oncologist. Dose Volume Histograms (DVHs) for 2D and 3D techniques were compared using TiGRT treatment planning system. Results: In 2D technique the mean dose of the cochlea and inner ear was 2624 ± 338.7(cGy) and 2718.3 ± 341.3(cGy), respectively. In 3DCRT technique the mean dose of the cochlea and inner ear was 2507±294.6(cGy) and 2581± 295.6(cGy), respectively. The mean dose of inner ear and cochlea in 3DCRTmethod was %5.3 and %4.6 lower than 2D, respectively Conclusion: The study of dosimetric parameters of the auditory system in treatment planning of two methods of radiation therapy showed that there was no significant difference between the doses of cochlea and inner ear in 2D and 3D methods ( Pvalues=0.86,0.85).Therefore in treatment planning of these two radiotherapy techniques, contour of cochlea can be replaced by inner ear.