Roentgen therapy of cancer of the larynx depends on the administration of sufficient x-rays to destroy the cancer while preserving the recovery power of the simultaneously irradiated, uninvolved larynx and laryngopharynx. The resistance to x-rays of the cancer and of the uninvolved laryngeal and pharyngeal mucosa is so similar that in order to destroy the cancer it is necessary to administer a dose which will also cause sloughing of the irradiated mucosa. The resulting denuded area promptly epithelizes, provided the subjacent vascular and connective tissues are healthy and have not been injured by preceding disease, operative trauma or previous irradiation. Microscopic evidence of retrogressive radiation changes in the vascular and connective tissues begin to appear about two to three months after such x-ray dosage. It is therefore preferable to terminate all roentgen therapy before this period of lowered resistance and not to repeat the treatment.
Tolerance of radiation injury diminishes