Bush__The_Essential_Physics_for_Medical_Imaging - Biomedical ...

TABLE 23-18. NUCLEAR REGULATORY COMMISSION (NRC) REGULATORYREQUIREMENTS: MAXIMUM PERMISSIBLE DOSE EQUIVALENT L1MITS aOccupational limitsTotal effective dose equivalentTotal dose equivalent to any individual organ(except lens of eye)Dose equivalent to the lens of the eyeDose equivalent to the skin or any extremityMinor «18 years old)Dose to an embryo/fetus bNonoccupational (public limits)Individual members of the publicUnrestricted area15050010% of adult limits5 in 9 months155010% of adult limits0.5 in 9 months1.0/yr0.1/yr0.02 in any 1 hr c 0.002 in any 1 hr c"These limits are exclusive of natural background and any dose the individual has received for medicalpurposes; inclusive of internal committed dose equivalent and external effective dose equivalent (i.e.,total effective dose equivalent).bApplies only to conceptus of a worker who declares her pregnancy. If the limit exceeds 4.5 mSv (450mrem) at declaration, conceptus dose for remainder of gestation is not to exceed 0.5 mSv (50 mrem).'This means the dose to an area (irrespective of occupancy) shall not exceed 0.02 mSv (2 mrem) in any 1hour. This is not a restriction of instantaneous dose rate to 0.02 mSv/hr (2 mrem/hr).mSv/yr (50 rem/yr). The dose to the fetus of a declared pregnant radiation workermay not exceed 5 mSv (0.5 rem) over the 9-month gestational period and shouldnot substantially exceed 500 IJ,Sv (50 mrem) in anyone month. Table 23-18 liststhe most important NRC radiation exposure limits.In practice, the committed dose equivalent and committed effective dose equivalentare seldom used in protecting workers from ingesting or inhaling radioactivity.Instead, the NRC has established annual limits on intake (ALls), which limit theinhalation or ingestion of radioactive material to activities that will not cause radiationworkersto exceed any of the limits in Table 23-18. The ALls are calculatedfor the "standard person" and expressed in units of microcuries. ALls are listed forthe inhalation and oral ingestion pathways for a wide variety of radionuclides (Table23-19).TABLE 23-19. EXAMPLES OF DERIVED AIR CONCENTRATIONS (DAC) ANDANNUAL LIMITS ON INTAKE (All) FOR OCCUPATIONAL EXPOSED WORKERS(1991 NRC REGULATIONS: 10 CFR 20)DAC (~Ci/mL)'1-1251-131Tc-99mXe-133 (gas)3 x 10- 82 X 10- 86 X 10- 51 X 10-440308 X 1,0 4N/A"Multiply IlCi/mL (or IlCi) by 37 to obtain kBq/mL (or kBq).N/A, not applicable.