PT - JOURNAL ARTICLE
AU - Siegel, Jeffry A.
AU - Marcus, Carol S.
AU - Sparks, Richard B.
TI - Calculating the Absorbed Dose from Radioactive Patients: The Line-Source Versus Point-Source Model
DP - 2002 Sep 01
TA - Journal of Nuclear Medicine
PG - 1241--1244
VI - 43
IP - 9
4099 - http://jnm.snmjournals.org/content/43/9/1241.short
4100 - http://jnm.snmjournals.org/content/43/9/1241.full
SO - J Nucl Med2002 Sep 01; 43
AB - In calculations of absorbed doses from radioactive patients, the activity distribution in such patients is generally assumed to be an unattenuated point source and the dose to exposed individuals at a given distance is therefore calculated using the inverse square law. In many nuclear medicine patients, the activity distribution is widely dispersed and does not simulate a point source. In these cases, a line-source model is proposed to more accurately reflect this extended activity distribution. Methods: Calculations of dose rate per unit activity were performed for a point source and for line sources of lengths of 20, 50, 70, 100, and 174 cm, and the ratios of line-source values to point-source values were calculated. In addition, radionuclide-independent conversion factors, to convert exposure rate constants to dose rates per unit activity, for these line-source lengths at various distances were determined. Results: The calculated values, substantiated by published data, indicate that the inverse square law approximation is not valid for a line source until a certain distance is reached, dependent on the length of the line source. For the 20-, 50-, 70-, 100-, and 174-cm line sources, the dose rate values estimated by the inverse square law approximation are within approximately 10% of the values estimated using the line-source approach at distances of 20, 45, 60, 85, and 145 cm, respectively. At closer distances, use of the point-source model for a patient with an extended activity distribution will overestimate the radiation absorbed dose to exposed individuals, sometimes by a very significant amount. Conclusion: The line-source model is a more realistic and practical approach than the traditional point-source model for determining the dose to individuals exposed to radioactive patients with widespread activity distributions.