Radiation dose to various age groups from radionuclide impurities in 99mTc-pertechnetate (fission product 99Mo generator) radiopharmaceutical preparations.

Radionuclide impurities of radiopharmaceuticals do not provide any diagnostic information, but contribute to the radiation dose to the patient. For 99mTc, even small amounts of long lived radionuclide impurities may contribute significantly to the dose from 99mTc itself. In this preliminary study, estimates have been made for the radiation dose to specific organs and for the effective dose equivalent from impurities in 99mTc-sodium pertechnetate prepared from fission product 99Mo. In addition to 99Mo, 131I, 103Ru, 89Sr and 90Sr at maximum permissible levels as stipulated in the European Pharmacopoeia, 110mAg and 239Pu were taken as representative nuclides for beta-gamma emitters and alpha emitters. Using all of these radionuclides at such maximum permissible levels of impurity as stated in the European Pharmacopoeia, the total contribution from the impurities to the effective dose equivalent is approximately 30% of the effective dose equivalent from 99mTc-pertechnetate. In terms of specific organs, the liver and kidneys can receive doses of 3-4 times and 1-3 times the dose from 99mTc-pertechnetate itself. Although these are worst case calculations, a consistent approach should be reconsidered to limit the additional effective dose equivalent from impurities to e.g. 10% of the effective dose equivalent from 99mTc itself.

[Iodine 131: biokinetics, radiation exposure and risk assessment with reference to the reactor accident at Chernobyl]. / 131Jod: Biokinetik, Strahlenexposition sowie Risikoabschätzung im Zusammenhang mit dem Reaktorunfall in Tschernobyl.

Following the reactor accident at Chernobyl, this paper describes the biokinetics of radioiodine in man and discusses the radiation exposure resulting from intake of 131I. The risk of radiation-induced thyroid carcinomas and of congenital abnormalities is evaluated. Assuming a linear dose/risk relationship, one can calculate an increase in mortality from thyroid carcinomas amongst children in southern Germany of 100 to 101 per million children. For adults in southern Germany, and for the rest of the population in Germany, the figure is considerably lower. Gonadal dose from the 131I released is so small, compared with the annual natural radiation exposure, that it is not appropriate to discuss genetic effects.

[Results of SPECT thallium-201 of the myocardium in the diagnosis of coronary disease and the follow-up of percutaneous transluminal coronary angioplasty]. / Ergebnisse der 201Thallium-SPECT des Myokards zur Erfassung der koronaren Herzkrankheit und zur Verlaufskontrolle bei perkutaner transluminaler koronarer Angioplastik.

Sensitivity and specificity of 201Thallium-SPECT in rest-exercise studies were evaluated in 129 patients in comparison to coronary morphology. In addition, the results of 70 patients, examined before and after dilatation of coronary stenoses by PTCA were obtained. In this group, quantification of SPECT images was tested. Sensitivity in detection of CAD was 93%, specificity 84%. False negatives were most frequently found in the posterior wall. After PTCA 73% of the segments improved. With quantification, an increase of vitality by 11.6% and a decrease of the redistribution factor by a value of 8 was documented. 201Thallium-SPECT of the myocardium was found to be very useful to both evaluate CAD and follow-up interventional procedures. A quantification of slice-images is useful to objectively reveal therapeutic success.

[201Thallium single photon emission computer tomography (SPECT) in the functional evaluation of coronary stenosis changes. Results of a comparison of stress scintigraphic and coronary angiographic findings]. / Die 201Thallium-Single-Photon-Emissions-Computertomographie (SPECT) in der funktionellen Beurteilung koronarstenotischer Veränderungen. Ergebnisse des Vergleichs von belastungsszintigraphischen mit koronarangiographischen Befunden.

201TI-Single-photon-emission computed tomography (SPECT) was employed in 57 patients immediately after exercise, followed by a redistribution analysis 3 hours later. 44 patients had coronary artery disease as documented by angiography (of these, 27 patients had an earlier myocardial infarction confirmed). 13 patients produced normal angiograms. 201TI-SPECT revealed a sensitivity of 93% and a specificity of 84%. Referring to a subdivision of the left ventricle into anterior and posterior walls, sensitivity in infarcted segments (96%) was significantly (p less than 0.01) higher than in non-infarcted segments (71%). No difference in sensitivities was found comparing anterior and posterior walls. Specificity of segmental analysis was 92%. Evaluation of segmental pattern (positive or negative redistribution) in old infarctions revealed persisting 201TI defects as frequent as the combination of persisting defects with surrounding redistribution. Non-infarcted segments showed sole redistribution in 89% of the cases. Left ventricular 201TI-SPECT improves the anatomical definition of defects in 201TI uptake. It enhances the functional evaluation of changes in regional perfusion subsequent to pathological coronary morphology.

[Single photon emission computed tomography (SPECT). Principles, results, outlook]. / Die Single-Photon-Emissions-Computertomographie (SPECT). Prinzipien, Ergebnisse, Ausblick.

Methods, instrumentation, performance data, clinical use and results of SPECT are presented. Since SPECT is yielding functional tomograms, morphological data are not the major concern with this method. Essentially 99mTc labeled radiopharmaceuticals, 201Tl chloride or 133Xe gas are in current use. SPECT may be considered as a supplement to ultrasound in detecting space-occupying lesions of the liver (combined accuracy 95%). Cranial SPECT already allows quantification of regional cerebral blood flow following inhalation of 133Xe gas. The sensitivity of myocardial SPECT with 201Tl (three-dimensional reconstruction) at rest in patients with severe coronary artery disease was higher than 90%. To further develop SPECT as a functionally oriented supplementary method to other radiodiagnostic procedures, further improvements are required as to performance, reconstruction algorithms and radiopharmaceuticals.

Spontaneous hematologic recovery from bone marrow aplasia after accidental tenfold overdosage with radiophosphorus.

Two patients with polycythemia vera received intravenously an accidental tenfold overdosage of radiophosphorus therapy (60 and 50 mCi 32P, respectively). In both patients, the occurrence of hemorrhagic complications 3 wk after the 32P medication led to detection of the error and referral to our hospital. Upon admission they showed an agranulocytosis, severe thrombocytopenia, and bone marrow aplasia. In both cases, spontaneous recovery of the hematopoiesis was observed from day 40 posttreatment onward. In one patient, a slow but ultimately complete normalization of blood counts and marrow morphology took place, whereas in the other, a mild thrombocytopenia persists. Nearly 5 yr after the accidental overdosage, both patients are clinically well. Symptoms of polycythemia vera have not reappeared up to now. Attempts were made to evaluate the radiation dose absorbed by the bone marrow. In the first patient, the daily 32P excretion was determined from day 22 to day 60, whereas in the other patient a whole body count was performed on day 78 after administration. From these results, an approximate cumulative bone marrow dose of 10 Sv (1000 rem) could be calculated.

Estimation of age-dependent internal dose from radiopharmaceuticals.

The age-dependence of the radiation dose absorbed in a target organ or the total body is determined by the mass, size, shape and separation of the organs as well as by the metabolic behaviour of the radionuclide compound. Using values of the specific absorbed dose for adults, the age-dependent effective dose equivalents for 28 radiopharmaceuticals (62 radionuclides) were calculated by modifying the above mentioned values, considering radiation type, organ mass and source-target separation. From the results, the currently used mathematical models for the modification of values of specific absorbed doses in the adult prove to be of sufficient accuracy. In comparison with the few available values calculated by Monte Carlo-techniques, our method overestimates the specific absorbed fractions by a factor of four in the least favourable case. For practical radionuclide dose estimates, these deviations are of minor importance as long as the availability of reliable information on the metabolic behaviour of radionuclide compounds and radiopharmaceuticals as a function of age is extremely limited. Considering, however, both the parenteral administration and the short half-life of radionuclides used in paediatric nuclear medicine, this uncertainty in regard to the gastrointestinal absorption and the biological half-lives is of little consequence for the results of absorbed dose calculations.

Radionuclide biokinetics and internal dosimetry in nuclear medicine.

In this review the present status of internal dosimetry for radiopharmaceuticals is summarized. Basic concepts of calculating the age-dependent mean tissue dose and the distribution of the local tissue dose are presented together with the fundamentals of biokinetics. Based on these dosimetric and biokinetic concepts, values of the absorbed dose for numerous radiopharmaceuticals are compiled. The accuracy of internal dose calculations is discussed quantitatively.

Radioiodine: biokinetics, mean dose and dose distribution.

For the radioiodine isotopes I-123, I-125, I-131, and I-132 the mean tissue dose and local dose distribution in the epithelial cells of a follicle have been calculated and compared to each other. Moreover, dose factors have been estimated for I-131 as a function of age considering age-dependent ingestion (milk consumption) and inhalation rates. Thereby, besides age-dependent biological half-times and thyroid masses, the thyroidal iodine uptake was assumed to be independent from age and taken to be about 1.7 the normal for an insufficient dietary iodine intake as in the Federal Republic of Germany.