IN-VIVO FLUENCE RATE EFFECT IN PHOTODYNAMIC THERAPY OF EARLY CANCERS WITH TETRA(M-HYDROXYPHENYL)CHLORIN

Several parameters affect clinical trials in photodynamic therapy and influence the therapeutic outcome, Beside drug dose, light dose, drug- light interval and other variables, the fluence rate is a parameter th at can influence the therapeutic results, In this study we have evalua ted the fluence rate effect with a second-generation photosensitizer, tetra(m-hydroxyphenyl)chlorin (mTHPC) using a 7,12-dimethylbenz(a)anth racene induced early squamous cell carcinoma of the Syrian hamster che ek pouch as a tumor model. Following injection of 0.5 mg/kg of mTHPC, irradiation tests were performed at two drug-light intervals, 4 and 8 days, Wavelength and light dose were adapted from those applied routin ely in clinical trials. Irradiations at 652 nm were carried out with f luences ranging from 8 to 20 J/cm(2) delivered at fluence rates of 15 and 150 mW/cm(2), Similar tests were also performed at 514 nm with a f luence of 80 J/cm(2) delivered at fluence rates ranging from 25 to 125 mW/cm(2), At both wavelengths and drug-light intervals for a given fl uence, the higher fluence rates resulted in less tissue damage in tumo r and healthy mucosae, However, the lower fluence rates yielded slight ly less therapeutic selectivity, This study confirms that the fluence rate is of major importance in clinical PDT.