RADIATION PROTECTION 697 FEDERAL RADIATION COUNCIL July 6, 1960 Dear Senator Anderson: We have received the copy of your request to Dr. Allen V. Astin, Director of the National Bureau of Standards, for information concerning the relationship between Bureau of Standards employees and the National Committee on Radiation Protection and Measurements. As I expressed in my testimony before the recent hearings of your Committee, "Radiation Protection Criteria and Standards: Their Basis and Use," it is the feeling of the Federal Radiation Council that the existence of a strong and independent National Committee on Radiation Protection and Measurements is a very important factor in the field of radiation protection. The Federal Radiation Council is anxious to see the NCRP continue its important work. The question of membership of Government agency employees on the NCRP is currently under consideration by the agencies with membership on the Council. We will be glad to inform the Joint Committee if the Federal Radiation Council takes any action which might affect such membership or the role of the NCRP. Sincerely yours, Arthur S. Flemming The Honorable Clinton P. Anderson Chairman, Joint Committee on Atomic Energy Washington 25, D. C. APPENDIX 11 RELATIVE BIOLOGICAL EFFECTIVENESS* Statement prepared by V. P. Bond and J. L. Bateman Medical Research Center Brookhaven National Laboratory Upton, L. I., N. Y. Prepared for hearings of the Joint Committee on Atomic Energy, Congress 700 RADIATION PROTECTION Introduction Relative biological effectiveness (RBE) has been the subject of a number of publications, and material on the subject is sufficient in quantity to allow a large volume to be written, However, it is possible to present in relatively short summary for the points considered to be most pertinent to the present hearings. In the present report the defini tion of RBB, its determination, its theoretical importance, the difficul ties involved in its use, and values for health physics purposes are dis cussed. The report will be limited basically to a consideration of work that bears more directly on mammalian RBB values, and it will not be possible to review the extensive and fundamental work that has been done with micro organisms and plants. Definition of RBE It is generally recognized that absorbed dose is the single most important parameter determining the degree of biological effect from radiation exposure. This quantity indicates the total amount of energy absorbed per unit weight from the impinging radiation, and is expressed in tems of units of rads, where 1 rad = 100 ergs/gram. However it is also well known that, with different types of radiation (e.ge gamma vs neutron), or for the same type of radiation delivered at different energies, with all other physical and biological conditions identical insofar as is known, different quanti ties of absorbed dose are required to produce the same degree of a given biological effect. This is equivalent in pharmacology to the fact that similar drugs may require different dosages for the same degree of effect, and this difference is termed the "relative potency" of the two drugs. Simi RADIATION PROTECTION 701 larly, with ionizing radiation the difference in potency between two radiations, or the same radiation at two different energy levels, is taken account of in the term RBE. More formally, the RBB of a given radiation can be defined as the ratio of the absorbed dose of a "standard" radiation (usually X - or gamma radiation) to that of the subject or test radiation re – quired to elicit the same degree of a given biological effect (mortality rate, spleen - thymus atrophy, cataract formation, leukemia induction, etc).*. Thus if the 50 per cent lethal dose of gamma radiation in mice is 750 rad, and that for fast neutrons of a given energy spectrum is 250 rad, then the RBB under the circumstances for the fast neutrons in question is 3. In general, all factors including dose rate are kept comparable for exposure to the two radiations. Under some circumstances, however, it becomes questionable whether the physical (rad) dose rate or the biological ("rem") dose rate should be kept comparable. The term RBB is intimately associated with the term "roentgen equivalent man”, or "rem", and the term "RBB dose". The terms are intended to "normalize" the dose of radiations with different RBB values, and the rem, or RBE dose is mumerically equivalent to the dose in r or rads multiplied by the RBB of the radiation. Thus 200 rads of fast neutrons of RBB 3 are "equivalent" to 600 rads or rem of X - or gamma radiation (600 rad x RBB of 1). The terms rem and RBB dose are used primarily in health physics considerations, although they are convenient in radiobiology as well, when the limitations *An alternate but less satisfactory and rarely used definition of RBB involves the ratio of degrees of biological effect for identical absorbed doses of different radiations. |