A FOLLOW-UP OF NONINVASIVE TUMOR OXYGENAT ION USING DIFFERENTIAL REFLECTANCE

Hypoxia is a factor of radioresistance in the treatment of solid tumou rs. One way to radiosensitize these tumours is to use carbogen (95% O- 2-5% CO2) and it is important to irradiate when the increase in oxygen ation created by the inhalation is at the maximal level. The DADOT is a non-invasive item of equipment that allows one to evaluate the relat ive proportion of oxygenated and deoxygenated forms of haemoglobin in tissues. The principle used is to measure the evolution of the absorpt ion of red or infrared light by haemoglobin. Two light-emitting diodes at respectively 0.66 and 0.94 mu m are coupled in two optical fibres the distal ends of which are applied on the tumour. These wavelengths are absorbed differently by the oxygenated and deoxygenated forms of h aemoglobin. The light which is back-scattered towards the surface of t he skin is detected by an amplified photodiode through a third fibre a pplied on the tumour. The modifications of tumour oxygenation during c arbogen inhalation were followed for two tumour cell lines. They were also studied in a patient. These first results suggest that the DADOT is a reliable item of equipment that gives reproducible results and th at could be used routinely to monitor changes in tumour oxygenation in patients.