125 I Interstitial Implants in the RIF-1 Murine Flank Tumor: An Animal Model for Brachytherapy

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Abstract
The development of a model for interstitial brachytherapy that uses high-activity, removable 125I sources in the RIF-1 murine flank tumor is reported. Experimental end points are clonogenic cell and tumor regrowth delay assays. For the clonogenic cell assay, interstitial radiation is delivered at total doses of 500-10,000 rad at dose rates of 0.9-2.7 rad/min to cells in annuli of tissue in the tumor. Dose-survival curves are characterized by an initial shoulder followed by a straight (exponential) portion, with D0 [mean LD] similar to that of the curve obtained by external irradiation of the RIF-1 tumor in a self-contained Ca irradiator at similar dose rates. Tumor regrowth curves were obtained for minimum tumor doses of 500-5000 rad; marked tumor regression was observed with minimum tumor doses as low as 2000 rad, but results are not as reproducible as the results obtained with the clonogenic cell assay.