Effect of x rays on human sternal marrow circulation.

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As early as 1868, shortly after the rec~ ognition of the hematopoietic function of bone marrow, Bizzozzero (1) estimated that about half of the active marrow consists of blood vessels. The response of the cellular, hematopoietic component of human marrow to both physiological and pathological events has been studied in great detail; the reaction of the marrow blood vessels under similar conditions has received relatively little attention. The disappearance rate of a locally deposited radioactive substance from the sternal marrow has been shown to be a reasonable measure of the effective capillary blood flow of that organ (2). Hematopoietic cells are known to be most vulnerable to the damaging effects of x rays (3), but little is known of the effects of x rays, if any, on sternal marrow blood flow. It seemed pertinent, therefore, to study the radioisotope clearance from the sternal marrow of patients who had received irradiation in that region. The half-time clearance of I131 Hippuran from the sternal marrow was used as a measure of effective blood flow and was determined by a technic previously described (2). Fifteen male patients who had received x-ray treatment to the mediastinum for malignant disease were the subjects of the study. Histologic or cytologic examination of the marrow was not performed because we wished to minimize the number of procedures for the patients and to avoid any manipulation of the marrow prior to the test. The clinical data and the results of the study are shown in Table I. The mean half-time clearance of I131 Hippuran for the test group was 28.6 ± 17.3 seconds. There were considerable scattering of the data and overlap with normal values. No correlation could be found between the half-time clearance, the postirradiation interval and the calculated x-ray dose. An exposure dose of 3,000 to 4,700 R to the sternal area delivered in three to four weeks has been reported to produce severe depression of the irradiated marrow (4). In a subsequent study Sykes et al. (5) found marrow regeneration failure in 96 per cent of the patients who received 3,000 R or more to the sternum. Examination after irradiation (from one and a half to eightyfour months) revealed fatty replacement of the marrow, and it was proposed that the inability to regenerate might be due to a permanent alteration of the vascular supply. In the light of reported findings, it seems reasonable to assume that the majority of the patients in the present study had a fatty sternal marrow, since 14 of the 15 had received more than 3,000 R to the sternal region. The results of this study indicate some alteration in marrow blood flow following irradiation. In view of the wide scatter of the data and considerable overlap with the normal, however, it would appear that the disturbance in marrow circulation is probably not the major factor in the failure of marrow regeneration.