Radiosensitivity of Tumors

Radiosensitivity is a term used to designate the reaction of cells to radiation, and the radiotherapy of malignant disease is based upon the difference in radiosensitivity between neoplastic cells and the normal cells which surround them. The factors that enter into radiosensitivity are many. The general condition of the patient often has a most important influence on the behavior of the tumor under treatment, and the metabolic activities of tumor cells are likewise important in determining sensitivity. There is a definite relationship between the grade of malig-nancy of a tumor and its reaction to radiation, since the latter is in direct ratio to the rapidity of its growth. Indeed, the law of Ber-gonie and Tribondeau states that tumors composed of rapidly multiplying cells, especially those of the embryonal type, are highly susceptible to radiation. From the practical point of view, radiologists consider the em-bryonal type of tumor especially favorable to radiation; adenoma and adenocarcinoma have a tendency to produce glandular structures which render them more resistant; epidermoid carcinoma, arising from squamous cells, is markedly radiosensitive; and osteogenic and neurogenic sarcomas are the most resistant of neoplasms. The location of a tumor is often an important factor in its reaction. Tumors growing in bone are many times invulnerable to repeated radiation, and mammary tumors, because of their growth in the fatty tissues of the breast and axilla, are extremely difficult to treat. In addition to these factors resident within the tumor itself or based upon its location, many other conditions contribute to the sensitivity or resistance of the tumors to radiation. Among these may be mentioned active infection, which interferes with successful radiation; indeed, the inflammatory process may be aggravated, and in many instances the growth of the tumor cells is accelerated. In cancer of the mouth, microbial infection unfavorably influences efforts to control maligniancy.