Dosimetric comparison of different radiotherapy techniques in graves' opthalmopathy

The purpose of this study is the dosimetric comparison of advanced radiotherapy techniques such as Volumetric Modulated Arc Therapy (VMAT) and Intensity Modulated Radiation Therapy (IMRT) with conventional 3D Conformal Radiation Therapy (3DCRT) technique in the treatment of Graves Ophthalmopathy. For 16 patients with Graves' Ophthalmopathy, 3DCRT, IMRT and VMAT treatment plans were made. Selected patients are patients who have received 3DCRT treatment before. Patients' computed tomography (CT) images were transferred to Monaco treatment planning system where IMRT and VMAT plans were made. Three different treatment tecniques were designed to give 20 Gy in 10 fractions over the entire period of two weeks. Conformity Index (CI), Homogeneity Index (HI), D05 (dose taken by 5% of volume), D01 (dose taken by 1% of volume), minimum, maximum and mean dose and the duration of treatment were compared between three different techniques. Advantages and disadvantages of the techniques have been evaluated statistically. From the comparison of 3DCRT, IMRT and VMAT treatment planning techniques, conformity index and homogeneity index values which are the most important criteria for the target volume were obtained the best for VMAT plans (p<0.001). The values of the IMRT technique were found to be better than those of the 3DCRT technique (p=0.000 for CI, p=0.005 for HI). There was a statistically significant difference between 3DCRT, IMRT and VMAT in terms of Monitor Unit (MU) values, stating the least amounts for 3DCRT (p=0.000). There is a statistically significant difference between IMRT and VMAT in favor of IMRT (p=0.003). For the lens doses, the maximum dose values were below the limits for all techniques, and statistically significant differences were found between the planning tecniques IMRT and VMAT plans in favor of VMAT (p=0.009). For the mean dose of lenses, the 3DCRT technique gave superior results compared to both the IMRT technique (p=0.003) and VMAT (p=0.002). There is no significant difference between VMAT and IMRT plans. When the maximum doses for optic nerves, lacrimal glands, and retinas were examined, significant differences were found in favor of 3DCRT technique for lacrimal glands (p <0.023); for optic nerves, there is significant difference between 3DCRT and VMAT in favor of 3DCRT (p <0.017) and both techniques had lower doses than those of the IMRT technique (p <0.002). When the maximum doses of the retina were examined again, there was no significant difference between IMRT and VMAT, but better results were obtained than the other two methods with 3DCRT technique (p <0.023). For eyes and optic quiasm, 3DCRT technique is clearly advantageous (p<0.013) when the mean doses are considered. VMAT plans were found to be more advantageous than IMRT plans (p<0.041). As a result of this study, it has been shown that the IMRT and VMAT techniques are feasible as an alternative to 3DCRT.