Tumour oxygenation is important in clinical radiotherapy because hypox
ic cells are radioresistant. Knowledge of the stale of tumour oxygenat
ion would be advantageous for maximising effectiveness of treatment. A
prototype fibre optic fluorosensor for measuring low (radiobiological
ly relevant) levels of oxygen is described. Based on oxygen quenching
of the fluorescence of an excited fluorophor immobilised in a polymer
at the end of an optical fibre, the sensor shows promise in overcoming
some of the limitations of existing oxygen sensor systems. The protot
ype fibre optic sensor operates most effectively in the 0-2% oxygen ra
nge with fast response and settling times. Preliminary results from me
asurements in tumours are presented.