Scab diameters on pig skin resulting from hot particle exposures under varying conditions.

The National Council on Radiation Protection and Measurements (NCRP) in NCRP Report Number 106 recommended a limit of 10(10) beta particles emitted from radioactive particles with sizes less than 1 mm (hot particles) to prevent acute deep ulceration. This recommendation was determined, in part, by regressing the diameter of the scabs induced by fissioned 235UC2 hot particles as a function of the logarithm of the number of beta particles emitted from the sources for one study. To validate this recommendation and the approach used by the NCRP, external irradiations of pig skin using radioactive sources of less than 600 microm in the largest dimension were carried out. The hot particles used included fissioned 235UC2 and activated 170Tm, 175Yb, and 46Sc. Results indicated a strong correlation between scab diameter and dose for scabs induced using fissioned 235UC2, activated 170Tm, and 46Sc, but not for 175Yb. The correlation value decreased with decreasing beta particle energy, with the exception of 46Sc, which had scabs with diameters greater than twice the maximum beta particle range. The larger scabs from 46Sc are thought to be due to dose contributions from the gamma rays. The results also give an ulceration threshold less than that given by NCRP to prevent acute deep ulceration. It was concluded that regression analysis of scab diameter as a function of either number of beta particles emitted from the hot particles or dose did not yield either precise or accurate thresholds but was useful in determining probable ranges of doses which lead to scab induction.

Scab incidence on pig skin resulting from hot particle exposures under varying conditions.

External irradiations of pig skin using radioactive sources of less than 600 microm in the largest dimension (hot particles) were carried out. The objective of the study was to determine a threshold for scab induction. Hot particles used included fissioned 235U and activated 170Tm, 17SYb, and 46Sc with maximum beta-particle energies of approximately 1.8 (average), 0.97, 0.47, and 0.35 MeV, respectively. The photon emissions from the fissioned 235U were about 1 MeV per disintegration. The photon emissions from 46Sc were 0.89 and 1.12 MeV, with 100% abundance. Photon emissions from 170Tm and 175Yb were negligible. Responses followed cumulative normal probability distributions; thus, no true thresholds could be determined. Hence, 10% and 50% scab incidence rates (ED10 and ED50, respectively) were determined using probit analysis. For dose averaged over 1 cm2 at a depth of 70 microm, the ED10 (and 95% confidence limits) were 5.1 (2.7-7.2) Gy for 46Sc, 1.3 (0.89-1.8) Gy for 175Yb, 2.8 (1.9-3.5) Gy for 170Tm, 8.5 (5.7-9.8) Gy for on-skin fissioned UC2, and 4.5 (0.9-7.2) Gy for off-skin fissioned UC2. The ED50 values were 12 (8.8-17) Gy for 46Sc, 6.0 (4.3-9.7) Gy for 175Yb, 5.9 (5.1-6.7) Gy for 170Tm, 11 (9.9-19) Gy for on-skin fissioned 235UC2, and 11 (6.2-14) Gy for off-skin fissioned 235UC2.

Effective half-lives for patients administered radiolabeled antibodies and calculated dose to the public in close proximity to patients.

Effective half-lives (T(e)) for radiolabeled antibodies can be much longer than that of traditional radiopharmaceuticals, potentially resulting in larger doses to members of the public. Clearance-rate data from patients treated with radio-labeled antibodies (RABs) were obtained from ten institutions. Calculations were made to determine if a single- or bi-exponential clearance-rate model was statistically justified; the results indicated that the former model was justified for more than 95% of the data. Values of T(e) for the different RABs are summarized. To plan actions to limit doses to less than 5 mSv annually for individuals continuously close to the patient (at 1 m), dose rates from patients at the time of release also are given as a function of T(e).