Clinical method for evaluation of radiopotentiation with oxygen inhalation: a preliminary note.

Abstract

Since the observation was reported that in experimental systems the degree of oxygenation at the time of irradiation markedly influences radiation response (1–3), a number of clinical trials have been undertaken in hopes of exploiting the so-called “oxygen effect.” A current evaluation of hyperbaric oxygen inhalation during radiotherapy is difficult because of the absence of suitable controls in the published clinical reports (4–6). An additional approach is suggested by an experimental study employing spontaneous mammary adenocarcinomas in mice (7). In this investigation, the radiation-potentiating effect resulting from inhalation of 95 per cent oxygen-5 per cent carbon dioxide at atmospheric pressure was comparable to that obtained with hyperbaric oxygen. This communication describes the preliminary results of a clinical method which may prove suitable for studies of this type. Materials and Methods Patients with discrete bilateral pulmonary metastases were selected for study. The lung lesions were metastatic from histologically proved primary malignant lesions outside the thorax. Other prerequisites for inclusion were no prior chemotherapy or irradiation (to the chest) and the presence of several lesions of comparable radiographic size in each hemithorax. By random assignment, one hemithorax received irradiation with the patient breathing air and the other was subsequently treated during inspiration of 95 per cent oxygen-5 per cent carbon dioxide. A fifteen-minute equilibration or “soaking” time was used prior to irradiation. Both sides were treated daily (control side first) with parallel opposing portals of equal size for each side. Lesions for treatment and measurement were selected as much as possible from the same approximate location within opposite hemithoraces for each patient. A maximum tumor dose of 2,000 R delivered at the rate of 200–300 R per day was administered. This rather moderate dosage was selected to minimize difficulties in tumor measurements which occur at higher radiation doses because of radiation pneumonitis and fibrosis. The tumor volumes were evaluated by serial chest radiographs taken before and at variable intervals after irradiation. The period of observation after radiotherapy was usually at least two to three months. Arterial blood gas determinations were measured on three patients before and after inhalation of 95 per cent oxygen-5 per cent carbon dioxide at atmospheric pressure. As summarized in Table I, a consistent five- to sixfold increase in the partial pressure of oxygen in the arterial blood resulted from inhalation of this mixture within a five-minute period. Results and Discussion Table II gives the responses observed on the initial series of patients.