MRI and CT images fusion in radiation therapy of brain tumors

The main objective of radiotherapy of brain tumors is to spare the damage of normal brain tissue without compromising the total radiotherapy dose. That became possible with the introduction of magnetic resonance imaging (MRI) in treatment planning of brain tumors. Between January 2010 and December 2011 in the Department of Radiotherapy of National Oncology Hospital - Sofia was performed radiotherapy treatment planning using a fusion of images from MRI and CT in 25 patients. Of those with malignant brain tumors were 16 patients (64%) and 9 patients were with benign tumors (36%). Among patients were 4 children aged 5, 11 and 14 years respectively, while the remaining patients were at a mean age - 37,5 years. 15 of them were male (60%) and 10 women (40%). All patients were after surgery and had a residual tumor seen on MRI or CT study. All patients were immobilized with individual thermoplastic mask and were scanned on CT and MRI with slice thickness 5 mm. The images were transferred to the treatment planing system and the fusion is made by mutual information automatically. The gross tumor volume (GTV), planning target volume and organs at risk were drawn and the radiotherapy is performed. Follow-up is made on fortieth day and on the sixth month after radiotherapy with MRI or CT study. The preliminary studies clearly show the advantage of fusion of MRI and CT for lesions located in the cerebellum, sellar and parasellar region and base of the skull which are the most of our patients. In conclusion we can say that despite of the small number of patients who underwent treatment planning using fusion of MRI and CT imaging this method has a significant advantage in identifying GTV compared with other methods (treatment planning using only CT or only MRI)