Photodynamic therapy of experimental intraocular retinoblastomas--dose-response relationships to light energy and photofrin II.

The destructive effect on tumour tissue and on normal eye tissue of photodynamic therapy has been investigated in rat eyes containing fast growing retinoblastoma-like tumours. Tumour response was described in terms of local control 90 days after treatment. The curability increased up to a maximum when large Photofrin II doses or light energy doses were administered. Early damage of conjunctiva or cornea also increased with large treatment doses and was an important limitation factor for improvement of the curability in the current model. The level of normal tissue damage decreased rapidly with increasing intervals between administration of Photofrin II and light, suggesting that conjunctival or corneal damage may not be a limitation factor 3-5 days after Photofrin II administration. A reciprocal relationship between light energy doses and Photofrin II doses was demonstrated both for curability and for the normal tissue damage. The results suggested that 2.5 mg/kg Photofrin II in combination with an extended light irradiation provoked less normal tissue damage than 10 mg/kg Photofrin II in combination with an equivalent shorter light exposure in order to obtain 15% curability of the animals.