Absence of irradiation induced ischaemic temporal lobe damage in patients with pituitary tumours.

This study was undertaken to confirm the belief that modern day external beam radiotherapy for patients with pituitary tumours should not be associated with any ischaemic temporal lobe damage. Using the oxygen-15 steady state inhalation technique and positron emission tomography regional temporal lobe blood flow, oxygen extraction fraction and oxygen utilisation were measured in 10 normal volunteers and 11 patients with pituitary tumours treated by irradiation. The patients were studied between 1 and 10.9 years after radiotherapy. We found that temporal lobe oxygen utilisation in the irradiated group (mean 2.11 +/- 0.23 ml of O2/100 ml tissue/min) did not differ from the normal group (mean 2.13 +/- 0.26 ml of O2/100 ml tissue/min). This suggests that total doses of between 35 and 56 Gy, delivered in fractions of less than 2 Gy, can be given to a pituitary tumour without demonstrable damage to normal temporal lobe.