A comparison of the doses received by normal cranial tissues during different simple model conventional radiotherapeutic approaches to pituitary tumours.

This aim of this study was to compare the doses received by critical cranial organs when three different radiation techniques were used to treat pituitary tumours. Cranial computed tomography scans of a RANDO phantom and 30 patients were used for pituitary macroadenoma radiotherapy treatment planning. For each slice, target volumes and other critical organs were contoured and three techniques were applied: (A) two parallel-opposed lateral fields, (B) two oblique fields (45°) in coronal plane and (C) two parallel-opposed lateral and anterior fields while the head was tilted 45° in the sagittal plane. The doses received by the target volume and the critical organs for each technique were calculated for all patients. Irradiation was repeated three times for each technique. Finally, the doses that reached the organs of interest resulting from these techniques were compared. The dose delivered to the temporal lobes was 105, 9 and 72 % of the prescribed dose using techniques A, B and C, respectively. The dose received by the cochlea was the lowest in technique C (27 % of prescribed dose) compared with techniques A (79 %) and B (48 %). All techniques delivered 100 % of the prescribed dose to the chiasma. Technique A increased the dose to temporal lobes and the cochlea to such an extent that they exceeded the tolerance dose. Technique B spared the temporal lobes better than technique C; however, technique C was preferred since the dose received by the cochlea in this case was the lowest of all techniques. None of the techniques spared the chiasma.