Dependence of the Risk of Encephalopathy on the Radiotherapy Volume after Combined Surgery and Radiotherapy of Invasive Pituitary Tumours

Summary

 The effectiveness of radiotherapy in reducing tumour recurrence of pituitary adenomas is well documented. On the other hand, the risk of side effects to the surrounding central nervous system normal tissue should not be underestimated. This retrospective study includes 58 patients with subtotally resected pituitary tumours. Photon from a 5,7 MV linear accelerator of a 60 cobalt unit with a source-isocenter distance of 80 cm were used throughout for treatment. The doses per fraction ranged from 45 Gy to 60 Gy. For a direct comparison of the different fractionation schedules, the biological effective total dose with 2 Gy per fraction was calculated for all the different application schemes with doses per fraction longer or smaller than 2 Gy. To do this, a fractionation sensitivity of the normal cerebral tissue by an □/□ value of 2 Gy was assumed. Encephalopathy developed in 17 cases (28 percentage) after follow-up times of more than 5 years. Pathological CT- or MRI-findings were seen in 13 cases.

 Two factors were important for the genesis of radiogenic encephalopathy:

1.*Multivariate analysis revealed that the risk of encephalopathy was associated with the radiation volume.

2.*The location of the upper field border line was the strongest prognostic factor associated with the risk of encephalopathy (p<0.05).