Volumetric Modulated Arc Therapy (VMAT) make a difference in retro-orbital irradiation treatment of patients with bilateral Graves’ ophthalmopathy. Comparative analysis of dosimetric parameters from different radiation techniques

Background Graves’ ophthalmopathy is the commonest extrathyroidal manifestation of Graves’ disease. Treatment options include steroid therapy, corrective/decompressive surgery, radiation therapy or combination of these approaches. Aim Our purpose was to investigate if retro-orbital irradiation with Volumetric Modulated Arc Therapy (VMAT) yielded better target coverage and dose sparing to adjacent normal structures compared to 3-Dimensional Conformal Radiotherapy (3DCRT) and Lateral Opposing Conformed Fields (LOCF). Methods Fourteen consecutive patients diagnosed with bilateral Graves’ ophthalmopathy were prospectively recruited into this study from August 2012 until August 2014. An individual VMAT, 3DCRT and LOF plan was created for each patient. Conformity Index (CI), Homogeneity Index (HI) and other dosimetric parameters of the targets and organs-at-risk (OAR) were analyzed in all 28 orbits compared between the different techniques. Results CI generated by VMAT was superior to that produced by 3DCRT(p<.001) and LOF (p<.001). As expected, 3DCRT was also superior to LOF (p=.007). Regarding the OARs sparing dose (lens, globes, retina and lacrimal glands), VMAT showed a significant benefit when compared with 3DCRT and LOCF, with no differences between the two latter techniques. Conclusions VMAT should be preferred over 3DCRT and LOF for bilateral Graves’ ophthalmopathy treatment.