Radiation Studies on a Mammary Carcinoma of Mice *

In the field of radiotherapy of neoplastic disease the development of higher voltage radiation and neutrons has necessitated the determination of their relative effects, compared with lower voltage radiation. Clinically this important information can be gathered only after a period of years. However, much information may be gained by the use of animal tumors as experimental test objects. In this paper we wish to report some observations carried out on an animal tumor which seems ideal for the above-mentioned purposes. Before doing so, however, a brief summary of the literature will be given. In 1920, Wood and Prime1' determined the lethal dose of x-ray for two animal tumors, finding that approximately five erythema doses delivered to Sarcoma 180 in vitro prevented growth upon subsequent implantation, and that approximately four erythema doses were similarly effective for a mouse mammary adenocafrcinoma (Carcinoma 63). Wood' later found that 180 to 195 minutes of radiation were lethal for the Flexner-Jobling rat carcinoma, it being therefore more radiosensitive than is Sarcoma 180. Subsequently'0 he determined that the lethal dose for rat Sarcoma 10 varied from 300 to 330 minutes, or, following the above standards, to be in the neighborhood of six erythema doses. In all of this work the tumors were irradiated in vitro. Packard' translates these figures into lethal doses of 1950 roentgens for the Flexner-Jobling rat carcinoma and 3240 roentgens for rat Sarcoma 10. On this basis, the lethal dose in vitro for Sarcoma 180 would be 2600 roentgens. In 1932 Packard4 repeated Wood's work with Sarcoma 180, using 550 kilovolt x-rays but irradiating only 12 to 24 tumor particles with each of only four doses. He found the lethal dose for this tumor to be