The Effect of Roentgen Rays on the Growth of Mouse Sarcoma 180 Irradiatedin Vivo

IN a previous study (1) the effect of 200 kv. roentgen rays on Mouse Sarcoma 180 in vitro was investigated. It was found that the viability of the mouse sarcoma was completely destroyed by an exposure to a dose of about 2,800 roentgens of filtered roentgen rays. It was further shown in this institution that the injurious action of filtered roentgen rays on the proliferating capacity of sarcoma cells was decidedly increased when the tumor tissues were irradiated upon the surface of a paraffin phantom. The back-scatter obtained by this method was found to be 30 per cent (2). Later we measured the depth dose by means of the transplantable tumor, using a paraffin phantom. The percentage depth dose at 2, 6.7, and 9.8 cm. was found to be 97, 86, and 54, respectively (2). These values agree reasonably well with the depth doses determined by ionization measurements made under similar conditions. In the irradiation of the tumor tissues in vitro, they are completely isolated from the surrounding normal tissues, blood vessels, tissue fluid, etc. Therefore, it is possible to observe the direct action only. However, from studying the biological effects of roentgen rays in vivo and comparing the results with those obtained by experiments in vitro, it may be possible to calculate the extent of the direct and indirect actions of radiation upon living cells. The following experiments were carried out with the object of testing this supposition. Materials and Methods The Mouse Sarcoma 180 was selected for the present study, the behavior of which in mice has been reported elsewhere. It may be of interest, however, to summarize its manner of development, since this may have a bearing upon the present investigation. A graphic illustration of a number of more or less typical examples of the progress of normal tumor implants in animals may show this development clearly (Fig. 1). When pieces of Mouse Sarcoma 180, each weighing about 6 mg., and measuring about (2 mm.)3 are inoculated subcutaneously in the lateral thoracic region by trocar, many of these transplants grow in spherical or in ovoid form, becoming flattened on their deeper aspect during the first week. As the tumors grow larger, many of them develop pressure necrosis at the subcutaneous parts of the tumors as early as the second week, and subsequently cause the deaths of the animals from toxemia, septicemia, and nutritional failure in about three weeks from the time of transplantation (Fig. 1, Nos. 4, 5, 6, 7). Some of the large tumors ulcerate, become infected and slough, and eventually regress and disappear completely (Fig. 1, Nos. 10, 11), while others grow normally for two to three weeks and then regress (Fig. 1, Nos. 12, 13, 14). The former cases we call spontaneous cures, and the latter cases, spontaneous regressions.