Evaluation of absorbed doses for photon and electron to the urinary bladder wall considering radiosensitive cells

Watanabe, Yoko ; Kinase, Sakae   ; Saito, Kimiaki  

From the standpoint of radiological protection and diagnostic procedures, dose evaluation of the urinary bladder is important since the radionuclides entered the body are metabolized and partially excreted by urine. A reliable bladder dosimetry model should consider radiosensitive cells in the bladder wall. In the present study, photon and electron SAFs to the germinal basal cells (radiosensitive cells) in the bladder wall (depend on the degree of the bladder stretch: 70-140m, cell's diameter: 5-10m) as well as the bladder wall surface were evaluated using Monte Carlo code, EGS4. S values were also evaluated for nine radionuclides:C, N, O, F, Sr, Sr, Y, Tc and I. Consequently, the photon SAFs to basal cell layers in the energy range 10-30keV are significantly larger than those of the whole bladder wall. The electron SAFs in all cases increase as the electron energy increases in the range 10keV-4MeV, indicating that electron SAFs to the bladder wall are not constant as described in ICRP Publ.30. As for S values, discrepancy was observed between the result of this study and conventional values, particularly in low energy region. These results demonstrate that determining the depth of radiosensitive cells is necessary for realistic dose evaluation.