Some factors altering the severity of acute radiation pneumonitis: variation with cortisone, heparin, and antibiotics.

Abstract

Most of Us justifiably regard the lungs as relatively radioresistant. It is only when large ports are irradiated to moderately high doses that we begin to see clinical symptoms of radiation pneumonitis. Among the many known factors which influence the severity of such symptoms are the type and extent of superimposed infection, status of pulmonary function prior to this additional damage, and the general condition of the patient. Time-dose-volume factors are also important, but their relationships to radiation pneumonitis remain poorly defined, particularly in patients with pre-existing lung disease. Symptom-producing reactions will be kept to a minimum if field sizes are small and if doses are fractionated and kept as low as possible. A certain number of reactions, however, are unavoidable. Therapy of radiation-induced lung reactions has been directed toward the decrease of fibrosis with steroids and the control of superimposed infections with antibiotics. The effects of these agents have been difficult to evaluate clinically, chiefly because of the highly variable course of the primary disease. In our previous study (9), whole chest irradiation was found to produce a striking reduction of total thoracic compliance, i.e., relation of pressure to volume. The decrease progressed for at least nine to twelve months following irradiation. Compliance of the thoracic cage changed very little; nearly all of the change in total compliance was due to the change in lung compliance. It thus appears that total thoracic compliance may serve as a measure of the lung damage produced by irradiation. In the present study this parameter was used to investigate the effectiveness of several agents in altering radiation-induced lung changes. Methods Female Sprague-Dawley rats weighing 150 to 175 grams were anesthetized with 4 mg. of sodium pentobarbital intraperitoneally. The whole chest was irradiated through a single anterior port. All radiations were given with the 220-kvp Picker x-ray therapy machine (T. S. D., 37 cm.; filter, 0.5 mm. Cu + 1 mm. Al, h. v. 1., 0.9 mm. Cu; 48 r/min.). Dose-time factors were varied as indicated in the section on results. Nonirradiated control animals were allowed to age with irradiated experimental animals. The relation of pressure to volume in the thorax was studied at intervals with the rat anesthetized and curarized. Immediately after anesthesia and injection of 10 mg. of succinylcholine intraperitoneally, a tracheostomy was made. A polyethylene tube was tied into the trachea and attached to a rat respirator. Paralysis followed in three to four minutes. Artificial respiration was then stopped and, after thirty seconds, lung volume was rapidly increased in 1-ml. increments with a tuberculin syringe. Endotracheal pressure was continuously measured with a resistance wire pressure transducer and a direct writing recorder.