Treatment of the human retinoblastoma cell line Y-79 growing in the athymic mouse eye with fractionated hyperthermia and/or radiation

Concentrated cell suspensions of the human retinoblastoma cell line Y-79 were injected into the eyes of athymic nude mice. Three to four weeks after implantation the eyes were treated with fractionated hyperthermia and/or radiation according to various protocols. Radiation was applied with 250 kV X-rays in fractions of 3 Gy, three fractions a week (3 x XT). Hyperthermia was applied once a week for 30 min at 43-45 degrees C (1 x HT). A coaxial microwave applicator (2450 MHz) has been developed for hyperthermia treatment of the mouse eye. The effect of the treatment was evaluated by visual observation of the eyes during a follow-up of several months, and by histopathological examination. No tumour regression was observed after hyperthermia alone (3 x HT). Treatment with 3 x XT or 3 x XT + 1 x HT initially caused tumour regression followed by regrowth in most cases. A treatment protocol of 6 x XT resulted in regrowth in 10 out of 15 eyes. However, after 6 x XT + 2 x HT regrowth was observed in only 3 out of 13 eyes. The difference between these two groups is statistically significant (P less than 0.05). Thus it is concluded that hyperthermia enhances the effect of radiation when the Y-79 cell line is transplanted to the athymic mouse eye, using the fractionation scheme presented here.