Dber Comments on Radiation Risks from Nuclear-Powered Artificial Heart Devices

Page 1

DBER COHNENTS ON RADIATIOX RISKS FROM NUCLEAR-POHERED ARTIFICIAL HEART EVICES The implantation of nuclear-powered artificial hearts raises not only the moral and ethical questions associated with the use of artificial organs i n general, but also several additional issues pertaining specifically to the potential radiological hazards of biological consequences of the radiation exyosure received from nuclear-powered artificial hearts. The radiation risks to the recipient,his family, the medical personnel involved i n implantation and subsequent care, and the general population a r e considered from both somatic and genetic standpoints, as w e l l as with respect to early and long-term effects. This docunent addresses itself only tothe possible Preliminary estimates of exposures. likely to result from the use of nuclear-powered artificial hearts were obtained from analytical and experimental studies sponsored by the Division of Applied Technology. For the heart recipient, the whole body dose would be about 8 2 rems p e r year. 14 rems per year fora male recipient, probably considerably higher fora female recipient depending on device location and orientation (with source end of device against ovary, the dose could be as high as 1,000 rems p e r year). recipient ' s inmediate family, dose rate estimates are based on the nature of family activities (sleeping, eating, watching TV, etc. ), time-distance data for these activities, and the radiation field expected in the vicinity of a recipient. from 0.6 to12 rems per year depending on whether recipient and spouse sleep in separate beds orin the same bed. The dose t o other family members i s very difficult to est dte ; a likely upper l i m i t would be about 0.4 rem per year. individuals on surgical teams would probably be held t o about 5 rems p e r year; medical attendants would receive about 0.001 rem per hour of contact with the patient. general population i s celculated from the radiation field around are qi pie nt, the estimated time-distance relationships of the recipient ' s interactions with the public, the number of surviving recipients and the total population. Based on assumptions of the number of potential candidates per year and the life expectancy of a person with a nuclear-powered artificial heart, the nmber of surviving recipients for the year 2000is estimated t o be 188,000 The gonadal dose would be about For members of t h e Spouse doses range The average dose tothe

Page 2

i n a population of 270,000,000. Of the 188,00~, 126,000 would be men of whoa 94,000 would have spouses and 62,000 would be women of whom 29,000 would have spouses. About 58,200 would be men under the age of 60, 11,200 would be women under the age of 55." This artificial heart population would increase the radiation exposure of each member of the general population by about incidence of heart disease i n the next 30 years and the emergence of artificial heart devices powered by other than nuclear means, it i s expected that the number of unrestricted artificial heart recipients with nuclear-powered devices would be ata maximum around the year 2000. Thus, the 0.0012 rem per year probably represents an upper limit of the dose t o the general population. It i s not expected that exposures a t any of these levels will lead to early radiation effects such as .local tissue necrosis and hematological o r immunological depression i n the recipients or in any other individuals. , Asto long-term effects, the induction of leukemia o r solid tumors in the recipients must be considered. the increased risk of malignancy from dzta available on people and experimental animals exposed t o radiation. National Academy of Sciences Committee report entitled "Biological Effects of Ionizing Radiation," (HEIR) it i s estimated (with qualifications)that the absolute risk of leukemia induction i n adults i s 1 t o 2 cases per million per year per rad. assumed that 188,000 individuals will have a device by the year 2000, they would be exposed t o approximately 15,400,000 man-rems, resulting in an estiraated 15-30 cases of leukemia annually. I n addition, 15 spontaneous cases of leukemia would be expected t o OCCUT annually i n these individuals a t the current leukemia death devices raises the number of leukemia deaths expected to ocr n in solid tumors in this group i s not great in view of the expected disease-associated life shortening of the implant recipients and the relatively long interval(in excess of 20 years) required for the mbi fe station of radiation induced neoplasms. Because of anticipated reductions i n the It is possible t o estimate Thus, the radiation froa the implanted The risk of induction of The increased cancer risks in groups other than the recipients, l.e., spouses, family members, and general population, are more difficult to estimate. interesting to note that the lower exposure estimate fora spouse I n order t o gain some perspective, it is * The aforementioned population figures were also supplied by DAT.

Page 3

(0.6 rem p e r year) is about the same as the maximum permissible dose for identified individuals of the population, whereas the higher estimate ( 1 2 rems per year) i s about 2.5 times the maximum permissible dose for radiation workers. Thus, the increased risk to the spouse i s about the same as that to radiation report that the numkr of excess leukemia deaths i n 123,000 spouses will be 0-3, i n 145,000 family members 0-1. leukeaia i n these groups are estimated t o be 10 and 12, respectively. According t o the BEIR report, the death rate f'rom radiation induced cancers of all types i s estimated t o be 17.5 per 100,000 per rem per year. Thus, the number of excess deaths f'rom cancers o f a l l types can be calculated t o be 13-260 for the spouses, and up t o 10 f o r family members. The spontaneous deaths a t the present (1971 estimate) U. S. death rate for cancer of all types (161 per 100,000) are estimated t o be about 2 0 0 f o r spouses and 230 for family members. It can be calculated from the assumption of the PXIR Spontaneous cases of Similar calculations for the general population of 270,000,000 yield the following estimates: 0-1 excess leukemia deaths; 2250 spontaneous leukemia deaths; u? t o 60 excess deaths from cancers of a l l types; and 435,000 spontaneous cancer deaths. The estimated testicular exposure from the device (about 14-15 rems per year) probably would not have a sterilizing effect in a young male until after about 20 years of exposure, butin an elderly male with existing impairment of spermatogenesis a t time of implant, such an exposure rate might well cause sterilization within seven o r nore years. ovary (about 1000 rems per year) would cause sterilization in a premenopausal woman and precipitate menopausal symptoms as well. The annual exposure t o a spouse sleeping i n the same bed (12 rem) would probably be sufficient to cause sterilization of a premenopausal wife i n about 20 years. Effects on a husband would be essentially the same as those on a male recipient. Ina fenale recipient the dose t o the With respect to genetic consequences, only broad and approximate statements are possible. It ha6 been estimated from the effects of exposure to experimental low-level chronic radiation that 200-300 rems are required to produce the same number of mutations as occur sponteneously per generation per individual ( t h e doubling dose). Several further assunptions must be made i n order t o present crude calculations of the increased morbidity and mortality expecced i n the next generation as a result of a f'ully implemented artificial heart program. These assumptions area stabilized U. S. population of 27 0, OOO, 000 With 100,000,000 babies born each generat ion ( i n

Page 4

addition t o those born to recipients) ; 188,000 persons with artificial hearts, 10,000 of whom have survived 10 years. If a mle recipient and his spouse su vive 10 yeax following implantation, each will have sustained a gonadal exposure o f 120-150 rems o r about one-half a doubling dose. It cm be cclculated *om estimates of the Ze;e and sex distribution and marital stsC,us of the recipients in the year 2000 that 2300 of the as sued 10,000 ten-year survivors will be married males under 60 years of age. reproduced nornally, they and t h e i r spouses would have contributed 2300 doubling doses t o the next generation. I n addition, mmbers of the generel po2ulation would have contributed 12,000-18,000 doubling doses as a result of being e qo sed, on the average, to a total of 0.036 rem up tothe neen age Of 1/200 t o 1/400 children born each generation are seriously handica;;ped o r die prenaturely because o f mutations inthe preceding generation, then the t o t s 1 doubling doses, 14,300 to 20,300, could result in 35 t o 100 defective children inthe. next generetion. During the sae period of time, net ural SWCeS of radiation will have resulted in 1,000,000 doubling doses t o defective infants.All these calculations are extrenely crude, but it would be irresponsible t o assume that no genetic damage tothe general population could result fron the exposures generated by: the implanted devices. If it i s postulated that they nave If it i s further assumed that aboilt . this p z rental population, producizg an estimated 2,500-5,000 ,I It must be emphasized that most of the risk estimates in this report are highly speculative. a t dose levels higher than those expected to result from the artificial heart program and were derived by linear extrapolation, a procedure whose application may not be entirely valid in this case. Furthermore, most of the calculations of the expected risks do not take into account the effect of dose rate. a single acute radiation exposure produces greater effects than the same dose given over an extended period of time. hold true also in man, it i s conceivable that the present risk. ~ estimates might be reduced. it i s t'ne opinion of the Division of Biomedical and Environmental Research that the hazards associated with the nuclear-powered artificial heart will be minimal and should not be a limiting factor in the development and experimental implantation of these devices. The moral and ethical questions pertaining to implementation of the artificial heart program must be considered separately. They are based on data obtained In experimental ani mls, If this should