The interaction of cis-platinum chemotherapy and high-intensity Iodine-125 brachytherapy was studied in C3H/He mice with MBT-2 tumors growing in the thigh. Brachytherapy was delivered by 3 Iodine-125 seeds of 10 mCi each implanted into the tumor. Ninety-six animals were randomly divided into 8 groups of 12 animals each. Each group was given either no treatment (control), cisplatinum alone or brachytherapy of 20, 40 or 50 Gy either alone or combined with cis-platinum. Cis-platinum 3 mg. per kg. was given every 5 days for 3 doses. The addition of cis-platinum enhanced the effects of Iodine-125 brachytherapy as shown by the end-points of tumor regrowth delay, local tumor control and median survival times. The sensitization enhancement ratio ranged from 1.2 to 1.9. Further experiments are to be conducted to study the normal tissue effect, therapeutic gain factor, effects of altering the time of administration of cis-platinum and the clinical use of high-intensity Iodine-125 for removable brachytherapy.
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