THE SHORTER-TERM BIOLOGICAL HAZARDS OF A FALLOUT FIELD becomes very small compared to the entrance air or ontrancetissue doses, and the depth-dose curve is far from flat. This type of “energy dependence” and the resultant biological effect. has been studied [18, 19], and is diseussed below. lt should be noted that while fallout gamma radiation has been termed ‘soft,’ only a very small percentage of the primary beamis below 100 to 200 kev under most. practical cireumstances [1], This is equivalent. in penetrating power in tissue to # highly filtered X-ray machine of 250 or higher peak voltage, or KVP. Thus the fallout gamma radiation must be considered quite penetrating in terms of biological effectiveness. Correlation of depth-dose patterns with bioluytcal effect.—-From the depth-dose considerations from the literature are collected, shows this to be true, The LDvalues for dogs and swine are given in the tables in terms of entrance air dose, as well as in terms of the entrance, midline and exit tissue doses. A better correlation between dose and effect would be expected if tissue dose is used unless (a) an energy dependence of biological effect is present, (6) marked differences in the shape of the depth-dose pattern exist, or (¢) strain differences in the degree of biological effect. exist. “Energy dependence” of biological effect as commonly used has inclided usually two separate phenomena to varying degrees, i. e., (a) a “true” or intrinsic energy dependence outlined above, wide variations in the dose in which dose deposition through the irradiated objects compared is well known and uniform, as air dose, would be expected with different same dose reflect different properties of the required for a given biological effect, expressed exposure conditions. A glance at Tables 1 and TJ, in which large animal mortality data "ih fate tak tt ty GEOMETRICAL, ENERGY FACTORS---EFFECT OF RADIATIONS ON MAN and quantitative differences in effect for the radiations, related to linear ion transfer (LET), or specific ionization; and (6) an “apparent” Taste I—LD» DOSES FOR DOGS EXPOSED UNDER DIFFERENT GEOMETRY CONDITIONS Radiation factors Method of expontire Radiation used Filter (mm >] HV (mm.) TSD (em,) Unilateral 280 KVP X-ray 14.2 Al Par- ‘Unilateral (from 1,000 KVP Xray (G. E, 12.7 Pb... S$. Pb ...] Wa... - throm above). (Plekerl. above), transmitied beam). abolic 0.6 Cu, LDa dose Dose rate (r/min.) wneef 2.18 Cu....[ 102......-. 1... 0. En- En Mid- Exit Reference ma trance ale trance tissue line tissue tissue 16 480: 562 382 160 Michaelson,» 3 450 405 360 202 Michaelson,* Unilateral... .) 2,0u0 KVP X- ray (GE, 68 Fe dn None... Bitateral... . Cnherent 1,000 KVP X- ray (0. E., radial heamst. 100Q KVP Xray (G. E., : radial heam) Bilateral... ...{ 20KVP XBilateral... Multti-Gouren Field. energy ray (G. E., cadiat beam). only). pum TSO {em.) 4a Ph... ./ 200. herent). radial beam). Unilateral ....{ Bomb gamma .{ 7 HVE ¢(mni.} |. oe 200 16 -| BS aaa 270 242 279 ‘Tullis, NMRI Aboutaio}. ag} ....| 30 . | 462.41. .| Varinble dependence secondary to differences These effects are considered Low energy radiation can be considered first, and beta radiation provides the absurd case because it penetrates only a few mm. in tissue. Thus “total body” beta radiation in reality resulis in a type of partial body radiation of one organ, (he skin. Energyis not deposited at depths sufficient to produce the “total body” irradiation syndrome of penetrating gamma radiation. Very low energy X or gammaradiation, e. g., 50 KVP X-rays, result in virtually the same picture as beta radiation when applied to the entire body surface, and the acule LDy here is of the order of several thousand r or rep to the skin, as opposed to a few hundred r for penetrating 312 265 266 268 Cronkite, NMRI @), 262 282 262 Gleiser, NMRI @2, Boohe + Bishop Rochester (23). 384 |... 8 Shiveley « et al. In mice, with essentially bilateral (uniform) wradiation [18], the transition occurs at somewhere between 80 and 135 KVP; at shout wwe fw we[e ween cefeweenee reys. This would be expected with type of partial body radiation. any with body size and the geometry of exposure. 80 KVP the LD, expressed as tissue dose or air dose, begins to rise rapidly. 448029 0O—-bs——6 qm). 43 Pb... herent). 316 «8. Michaelson, J. N. Shiveley and J. Howland, personel communteation. * Calculated or estimated; value not given in references cited. (24. 63FotIne Lb Bilateral. ...| Oo gamma... None...,..--' 10.8 Ph...JH8...... - Powe nae ay). Bond, NRDL (25). LB Not gefvanin report Tullis, NMR 3n2 As the beam energy increases, the effects of penetrating whole body radiation do appear, and the energy level where this occurs varies 1,000 KVP... ... 145 BBs Bond, USNRDL an. Bilateral.......{ Ta 402 260 vee af 225 425 256 . aah % 230 200... . - . uy 44 Ph...| 200.. .-.. Tallis, NMRI m7. 3 6.8 Fe. ...-.) 4.8 Ph... 130 He Man weneeenee 4a Fe (nherent), at 20 Fb. 2 110... --.. radial beam), 5a0 Tullis, NMRI 252 -| 3000 KVP..... S00 367 252 Baateral.......| 2.000 KVP Xray (G. E., Ls 252 282 Bhatersl.. Exit tissue 357 281 ray (@. E., Tadial beam), Midline Sig G (Inherent) ..] 2.0 pb... tissue a WG... fb Bilateral......- 1,000 KVP X- tissue alr} eo 100. .... beam). Entrance =| 3. High veria- |... ... ble. 1S Argonne(20). Bond, USNRDL 17). ble. Entrance 100 100... Prosser et at. High varia- Reference ma Cnheront: onty), Cot gamma. .| None... in penetration. below. LDdone weep Dose rate (ymin) 15... 2... .| 1,000 yds .| L000 yds. |} 880 |... (4). 7 Filter (rman.) None .......]..-.-....-.-] |.--..-.-.--- 210 Radiatlon factors Hadiatien used 05 Cu. O8Cul0 AL 256 eqporure .| Bomb gamma...) {G. E.) 271 Rochester, { Methud of -] MOK VE Xray Milateral.......| @O KVP Kany {@. E., radial nl Rochester. 75 Tarve [IY -LDg DOSES FOR SWINE EXPOSED UNDER DIFFERENT GEOMETRYCONDITIONS In the rabbit, (at). Rast, et a, Oak Ridge (25). the change oceurs at a higher KVP, probably near 150 KVP. With dogs, the LD,» for 100 KVP X-rays (midline tissue dose) is 1.4 times that for 250 KVP, thus the transition occurs somewhere between these energies. From Table II, it is seen that above 250 KVP, the LD, for dogs (bilateral X-irradiation, midline tissue dose) is independent of energy. No such data are available on larger animals the size of man; however, it appears likely from depth- dose curves that the transition would occur at 250 KVP or somewhat higher. The above “energy dependence” thusis seen to bein reality a pseudo energy dependence—if the radiation dose cannot be delivered te the vital tissues, “energy dependence” of effect cannot exist. This effect has nothing to do with relative biological effectiveness (RBE) in the strictuse of the term, although RBE frequently is used loosely to include it. As stated above, many of the radiations of concern in hazard evaluation are sufficiently energetic such that this factor is not large. The chief exceptions are bomb neutrons and beta radiation. With these radiations, however, the effect exceeds by far in magnilude the effect resulting from intrinsic RBE. A possible “true” energy dependence of biological effect on energy over the ranges of in-