401862 — April 1954 me CALCULATION OF RADIOACTIVE IODINE BETA RADIAMLIONOS DOSE TO THE BONE MARROW By James S. Ropertson, M.D., Ph.D., and Joun T. Gopwin, M.D. Medical Physics and Pathology Divisions of the Medical Department, Brookhaven National Laboratory, Upton, Long Island, New York (Accepted for publication September, 1953) HEN doses of 1!I of the order of 100 me or more are administered, as is sometimes done in the treatment of thyroid carcinoma, the assoctated irradiation of the hematopoietic tissues is the most important factor limiting the dose which the patient can tolerate. The radiation delivered to the bone marrow is usually estimated by assuming that the dose of radiation delivered to the bone marrow is individuals with their age, health and nutritional status and in a given individual there are variations from bone to bone and even from point to point in the same bone. The areas obtained in measurements made in twelve selected fields were: 19-4, 18-4, 17-2, 16-4, 15-8, 9-9, 9.2, 8-8, 8-0, 6-7, 5-1 and 4-0 per cent of the area of the field. The meanforthis series is 11-6 equal to that delivered to the blood (Rall, Foster, per cent. It is not areas, however, but volumes Yalow and Siegel, 1952; Marinelli and Hill, 1950), the method of Marinelli, Quimby and Hine (1948) being used to calculate the dose delivered to the blood. This method includes the assumption that absorption. It is easily shown that the relative areas represent the relative volumes. As a first approximation we shall assume that the orientation of the trabeculae is random. Consider a block of unit released and the energy absorbed in a unit volume two phases with the fraction, f*, of its volume in Robbins, Lazerson, Farr and Rawson, 1953; Seidlin, for the B-particle contribution to the dose the energy of a given tissue are equal. Although the hematopoietic portion of the bone marrowis a soft tissue, the tissue regarded anatomically as the bone marrow is characterised by the presence of interspersed bony trabeculae which absorb someof the energy released in the soft tissue. Therefore, the assumptions involved in the soft-tissue method of dose calculation are not strictly valid for bone marrow. An estimate of the energy absorbed in the bony trabeculae is which are significant in determining radiation height and width having its contents distributed in phase II as illustrated in Fig. 1. A section through A PHASE I — PHASE I —— derived in the presentarticle. A major requirementin establishing the required estimate is a value for the relative volume of the marrow occupied by bony trabeculae. This part of the problem was approached by measuring the bony areas of representative portions of normal appearing marrow from ribs and vertebrae obtained routinely at autopsy from adult patients dying of various 9~270=2 and eosin. Photomicrographs of one or more fields this block parallel to face AB has the fraction, f, of diseases.* Sections were stained with haematoxylin from each of the several bone sections were made on 45 in. Ektachrome film at low-power magnifica- COL 2 i ae tion. An effort was made to select representative fields with average distributions of trabeculae and marrow. The area occupied by the bony trabeculae was obtained by planimetry. It is apparent that any figure so obtained for the trabecular area must be regarded as an approximation only, because the structure and composition of bone varies among * Dr. Henry L. Jaffe kindly supplied several of the bone sections used in this study. its area in phase II. Of the sections parallel to face ACor to BC, a portion (1—f) will have none of their areas in phase II, while those in the remaining portion, f, will have f of their areas in phase II, so the average area for these sections is also f*. For other orientations of sections the averaging effect may not be so obvious, but since the sums of the areas multiplied by the thicknesses of the sections gives the volumes involved, for uniformly thin sections the average percentage area of phase II represents the percentage volume of phase II. 241 RECORDS: merository VL cottection MARSHALL BoxNe LEQ/CAL DEPT. FOLDER 2238 - 109 ISLANDS PYBLICATIONS The Medical Research Center Brookhaven National Laborator y Upton, L. L, New York