Comparison of three-dimensional conformal radiotherapy and intensity-modulated radiotherapy in radiotherapy of thyroid orbitopathy patients

Objective: Thyroid orbitopathy (TO) is characterized by inflammation of orbital tissues due to otoimmun thyroid disease. Eyelid retraction, chemosis, periorbital edema and eye movement disorders are among the findings of disease. Orbital radiotherapy is applied to the cases who does not respond other treatment modalities and is effective in 60-65% of cases. In this thesis our aim is to compare 3DRT, IMRT and hybrid RT techniques dosimetrically in patients with TO. Method: Treatment plans of 5 patients with TO were transferred to the treatment planning system. Treatment plans were performed using 3DRT, IMRT and hybrid RT techniques. Conformity index, homogeneity index and dosimetric parameters of 3 techniques were compared statistically. Results: IMRT and hybrid IMRT techniques were found to achieve more homogen dose distribution. Homogenity index of IMRT was significantly better than HI of 3DRT. However conformity indexes of 3 techniques were not statistically significant. 3DRT was found to achive lower lens and brain doses compared to other techniques. Hibrid RT technique was similar to IMRT technique dosimetrically. Conclusion: IMRT may improve treatment results in TO since it achives better dose distribution however it causes increase in lens and brain doses.