Further Studies on the Relation between Radiation Effects, Cell Viability, and Induced Resistance to Malignant Growth

Abstract

The expts. reported in this paper represent an extension of the author''s previous studies in this field with the use of mouse sarcoma, 180 as an exptl. subject. A tumor of known genetic constitution, the Bagg-Jacksen mouse carcinoma 755 expts. reported was grown in an inbred strain of mice the C 57 Y black. Irradiation of this tumor took place in vitro and in situ. The irradiation factors were 200 kV, 20 ma, 0.5 mm. Cu and 1.0 mm. Al filtration, HVL 0.9 mm. Cu, intensity 577 r/min. The doses ranged from 1200-5500 r/air and were given in one exposure. For the irradiation of tumors in situ, the animals were protected by a lead shield of 4 mm. thickness and the exposure took place through holes of 2.5 cm. diam. Male mice 18-25 gm. of wt. were used for the implantation of irradiated and non-irradiated control tumor fragments. As criteria of the irradiation effect the latent period, the number of "takes" and the size of the irradiated implants were used. The same indices were applied to tumors produced by the non-irradiated (control) implants. A dose of 3500 r/air applied to tumor particles of the Bagg-Jacksen mammary mouse carcinoma 755 in vitro permitted 58.6% takes, while a dose of 4500 r/air entirely prevented growth of the irradiated implants. Very valuable is the comparison of the author''s results obtained in this study with those obtained by other investigators seeking to determine lethal doses for various tumors irradiated either prior to implantation or in situ. In two tables 25 references are quoted. Evidence for quantitative disagreement as to the lethal dosages among the various investiga-tors is given. This is at least partly explained by the different technical procedure applied by the previous inyestigators. The dose of X-rays necessary to prevent an implant from producing a tumor does not differ widely from that required to destroy a tumor in situ, provided an inbred strain of mice is used. This is in agreement with previous observations. If it is true that tumors grown in hybrids require smaller dosages than those grown in inbred strains, as it appears from the evidence given in this paper and the previous publications, this would be an advantage for the therapy of cancer in man.