Radiation protection shielding computation of gamma photons produced in positron annihilation

Objective To study the best method of radiation protection shielding calculation for the gamma photon produced in positron annihilation.Methods With 18F as the typical of nuclide,different methods or literature about constant and the calculation of the TVL or recommended values were adopted to calculate and analyze the shielding thickness by lead as block material.Results The shielding thickness by the dose constant was calculated by point source model (0.142 μSv· m2· MBq-1 · h-1) and TVL of lead recommended by NCRP was the biggest:at the control area the unit thickness for lead shield was 7.562 × 10-4 mm· MBq-1 for one patient.While by the dose constant recommended by AAPM TG108 (0.092 μSv·m2 ·MBq-1 ·h-1) and lead TVL recommended by IAEA was the minimum.The unit thickness for lead shield at the control area was 4.982 × 10-4 mm · MBq-1 · patient-1,with difference of 36.2％.Conclusions The dose constant and the TVL value of lead from AAPM.TG 108 are recommended for the calculation.In shielding design attention should be paid to the distance protection,the separate toilet with shielding for patients,and the separate corridors beteen doctors and patients. Key words: Positron;  Radiation protection calculating;  18F;  Tenth-value layers;  PET