Monte Carlo simulation of in vivo measurements of 90Sr + 90Y bremsstrahlung.
The purpose of this study was to calculate the 90Sr + 90Y bremsstrahlung yield generated in bone quantitatively, and to determine the optimum conditions required for in vivo measurements of the yield, assuming that a given amount of contamination, due to the ordinary activities of 137Cs and 40K, is present within the human body. Several approximations in the distribution of activities in various body phantoms, simulating the human leg, waist and head, were made for simplicity. All the calculations were carried out using an in-house Monte Carlo code. The photon spectra incident on a detector window, of diameter 200 mm, positioned 1 mm from the surface of each phantom were obtained. A pseudo-peak of 90Sr + 90Y bremsstrahlung was observed at approximately 50 keV with a full width at half maximum of 60 keV (FWHM). The signal-to-background ratio, eta, where eta represents the ratio of the number of photons in the energy interval between 30 to 160 keV in the bremsstrahlung spectrum produced by 1 Bq kg(-1) of 90Sr and the background spectrum, which is assumed to comprise of 1 Bq kg(-1) of 137Cs and 60 Bq kg(-1) of 40K, was evaluated in order to determine the optimum measuring conditions. An optimum eta value of 0.0353 was obtained for the leg phantom, of bone diameter 30 mm, covered by a 1 mm layer of soft tissue. Combining the present calculations with the conventional measurements, a new and simpler method for evaluating the body burden activity of a beta emitter, such as 90Sr, is proposed.
Uehara
S
S
School of Health Sciences, Kyushu University, Fukuoka, Japan.
Endo
S
S
Takada
J
J
Hoshi
M
M
D001610:Beta Particles; D001822:Body Burden; D001842:Bone and Bones / Q000737:chemistry; D005720:Gamma Rays; D006801:Humans; D009010:Monte Carlo Method; D013326:Strontium Radioisotopes / Q000032:analysis*; D015021:Yttrium Radioisotopes / Q000032:analysis*
D013326:Strontium Radioisotopes; D015021:Yttrium Radioisotopes