Proceedings of The British Institute of Radiology Radiobiology work in progress, February 19, 1988

Experiments have been carried out that have demonstrated that the growth ofcells as multicellular spheroids confers resistance to photodynamic therapy. The human colon adenocarcinoma cell line, WiDr, was used, and drug exposure (10μg/ml Photofrin II for 24 h), washing and light irradiation were in the presence of 10% fetal calf serum. Irradiations were in fresh medium and under static conditions, and only spheroid sizes where there would be nohypoxic cells were used.