Radiation Protection Q&A

RAPHEX General Question 2001 G75: All of the following contribute about equally to the average annual dose equivalent received by a member of the U.S. population EXCEPT: A. Internal B. Terrestrial, other than radon C. Medical x-rays D. Nuclear medicine E. Cosmic

RAPHEX Answer to 2001 Question G75 D. Nuclear medicine Out of a total of about 3.6 mSv, nuclear medicine contributes about 0.14 mSv, and the others all contribute about 0.3 to 0.4 mSv each.

RAPHEX General Question 2002 G87: The annual average natural background radiation dose to members of the public in the United States, excluding radon, is approximately ___ mrem. A. 10 B. 50 C. 100 D. 200 E. 400

RAPHEX Answer to 2002 Question G87 C. 100 Radon adds another 230 mrem/yr. Man-made radiation, mostly diagnostic x-rays, is about 54 mrem/yr.

RAPHEX General Question 2003 G82: The principal hazard from indoor radon involves: A. Whole body dose from gamma rays B. Skin dose from betas C. Lung dose from alpha emission D. Bone dose from deposited radionuclides

RAPHEX General Question 2001 G78: The latent period for radiation-induced carcinogenesis (solid tumors) is about ____ years. A. 1 B. 5 C. 10 D E

RAPHEX Answer to 2001 Question G78 D. The latent period is 20 to 30 years

RAPHEX General Question 2002 G89: The currently accepted model of radiation dose versus effect used by regulatory agencies to determine dose standards is ____. A. Linear quadratic B. Exponential C. Cubic D. Linear, threshold E. Linear, no threshold

RAPHEX Answer for 2002 Question G89 E. Linear, no threshold Although there are valid arguments for other models in specific situations, the linear, no threshold model is the most conservative, and is in current use by regulatory agencies.

RAPHEX General Question 2003 G86: The radiation protection quantity which has been used in attempts to estimate the cancer risk from x-ray irradiation of personnel is _____. A. Exposure (X) B. Air Kerma (K) C. Absorbed dose (D) D. Dose equivalent (H) E. Effective dose (E)

RAPHEX Answer to 2003 Question G86 E. Effective dose (E) In NCRP Report 116 the Effective dose (E) attempts to weight the radiation dose to different organs by the relative cancer risk of each organ.

RAPHEX General Question 2001 G79: Perinatal death (at or around the time of birth) is MOST likely to occur as a result of irradiation in humans which occurs in the gestational period of: A. Implantation of the embryo B. Major organogenesis (21-40 days). C. Second trimester D. Just before brith (30-36 weeks).

RAPHEX Answer to 2001 Question G79 B. Major organogenesis (21-40 days) In early organogenesis the organ buds consist of a few cells, and the loss of some of these can result to a major defect which may not be apparent during gestation, but after birth is too severe to permit independent life.

RAPHEX General Question 2003 G88: According to NCRP there is a negligible increase in the risk of adverse effects to the fetus, compared with other risks in pregnancy, up to a total dose of _____mGy. A. 5 B. 20 C. 100 D. 500 E. 1000

RAPHEX Answer to 2003 Question G88 C. 100

RAPHEX General Question 2001 G81: Which of the following is true about film badges? A. Can measure total dose, but cannot distinguish between high- and low-energy x-rays. B. Can measure exposures of 2 mR C. Are insensitive to heat D. Are used to determine exposure by measuring the optical density of the film E. None of the above is true

RAPHEX Answer to 2001 Question G81 D. Are used to determine exposure by measuring the optical density of the film. Film badges cannot measure exposures below 20 mR. Placing filters over parts of the film allows one to estimate the proportion of dose due to x-rays in different energy ranges. Heat, e.g., exposure to intense sunlight, CAN cause film blackening.

RAPHEX General Question 2002 G94: According to NCRP Report No. 11, the recommended maximum annual dose equivalent for radiation workers’ whole body is ___ mSv and for the hands is mSv. A. 5, 5 B. 5, 50 C. 10, 100 D. 50, 50 E. 50, 500

RAPHEX Answer for 2002 Question G94 E. 50, 500

RAPHEX General Question 2003 G89: The NRC requires personnel to wear a radiation monitor if they are likely to receive _____% of the annual dose limit A. 90 B 50 C. 25 D. 10 E. 1

RAPHEX Answer for 2003 Question G89 D. 10 Prior to 1994 it was 25%, but since this date it has been set at 10%

RAPHEX General Question 2001 G86: When calculating radiation barrier thickness requirements, the use factor “U” refers to: A. The weekly dose delivered at 1m from the radiation source B. The fraction of operating time during which the area on the other side of the barrier is occupied C. The fraction of operating time during which the radiation is directed towards the barrier D. The fraction of the work week during which a particular individual is in the area of interest

RAPHEX Answer to 2001 Question G86 C. The fraction of operating time during which the radiation is directed towards the barrier The use factor can be difficult to calculate, so standard fractions can be used for the walls and floor.

RAPHEX General Question 2001 G87: A “controlled area” is defined as: A. Any area around a radiation facility where the exposure rate is above background B. an area that one cannot enter unless one is wearing a film badge C. An area where workers will not receive more than 5 mrem/week D. An area where the exposure of workers is under the supervision of the Radiation Safety Officer

RAPHEX Answer for 2001 Question G87 D. An area where the exposure of workers is under the supervision of the Radiation Safety Officer Workers can receive up to 100 mrem/week.

RAPHEX General Question 2002 G98: When calculating room shielding, the use factor U refers to: A. The weekly dose at the isocenter B. The fraction of operating time that the area in question is occupied C. The fraction of operating time that the beam is directed towards the barrier D. The fraction of the work week that the machine is in operation

RAPHEX Answer to 2002 Question G98 C. The fraction of operating time that the beam is directed towards the barrier. This is hard to estimate exactly, so standard fraction are generally used.

RAPHEX General Question 2002 G99: When designing shielding for an x-ray machine, regulations require that the barrier for a fully-occupied non-controlled area must be about ____ HVLs thicker than that for a controlled area. A. 50 B. 10 C. 6 D. 2 E. 1

RAPHEX Answer for 2002 Question G99 C. 6 The current annual MPDs are 100 mrem for non-controlled areas and 5 rem )5000 mrem) for controlled areas. This factor of 50 requires about 6 HVLs more shielding (2 6 = 64)

RAPHEX General Question 2003 G94: In the event of a 137 Cs “dirty bomb” explosion, regarding the use of potassium iodide pills, which of the following is true? A. KI should be taken as soon as possible B. KI should be taken if the thyroid has the potential of receiving a dose greater than 15 rem C. A dose of 130 mg per day is suggested for adults D. KI will offer no protection

RAPHEX Answer to 2003 Question G94 D. KI will offer no protection Sodium iodide is only used to protect the thyroid from the radioactive iodine released in a nuclear explosion. 131 I has a relatively short half-life, and would not be used in a “dirty bomb.”

RAPHEX General Question 2001 G91: In general, which of the following detectors has the greatest energy dependence for x- and gamma rays? A. Thin window geiger tube B. Air equivalent wall ionization chamber C. LiF thermoluminescent dosimeter D. NaI scintillator detector

RAPHEX Answer to 2001 Question G91 D. NaI scintillator detector The high Z of iodine makes it highly sensitive to low-energy radiation. This is because of the Z dependence of photoelectric interactions.

RAPHEX General Question 2003 G95-98: Match the most appropriate instrument to the procedure in each question. A. Liquid scintillation counter B. NaI well counter C. Geiger-Mueller (GM) counter D. Thermoluminescent dosimeter ( TLD) E. Ionization chamber survey meter G95: Gamma ray sealed source wipe test G96: Contamination survey for 99m Tc G97: Radiation survey of a diagnostic x-ray installation G98: Personnel monitoring

RAPHEX Answer for 2003 Question G95-98 G95: B. NaI well counter is an efficient device for measuring low-level gammas. It can also provide energy discrimination G96: C. A Gm counter has a fast response and the ability to detect low levels of gamma rays G97: E. An ionization chamber survey meter is capable of accurate x-ray dose rate measurements with minimal energy dependence G98: D. The small size and relative energy independence of TLK make it useful as a personnel monitoring device.

RAPHEX General Question 2001 G93: The basic consideration when disposing of radioactive waste in the sewer system is: A. Entrance into food and fresh water chain B. Contamination of the sewer system C. Fish death D. Risk to swimmers E. Evaporation into the air

RAPHEX Answer to 2001 Question G93 A. Entrance into food and fresh water chain Very low concentrations of radioactive materials, if ingested, can produce high localized radiation doses to internal organs.

RAPHEX General Question 2001 G94: A unit dose radioisotope is delivered to a hospital. The vendor supplies a calibration of its activity. Regulations require the hospital to do all of the following EXCEPT: A. Wipe test the package before opening it B. Treat the packaging material as low-level radioactive waste C. Independently verify the activity D. Quantify any residual activity left following use of the radioisotope E. Keep logs of receipt, use, and disposal (or storage) of all radioisotopes

RAPHEX General Question 2002 G100: After installation of a chest x-ray unit, which agency regulates its operation? A. NRC B. OSHA C. HICFA D. State

RAPHEX Answer to 2002 Question G100 D. State Once installed, x-ray units are regulated by the state. Mammography units are also regulated by the FDA, under MQSA standards. The FDA regulates the manufacture and installation of x-ray devices, under 21 CFR The NNRC regulates the use of “man-made” radioactive materials such as Co-60 units and brachytherapy sources.

RAPHEX General Question 2003 G100: “ALARA” stands for: A. As Long As Reasonably Allowable B. As Low As Responsibility Attainable C. As Low As Reasonably Achievable D. As Little As Possible RadioActivity

RAPHEX Answer to 2003 Question G100 C. As Low As Reasonably Achievable ALARA is a basic tenet of radiation protection. Obviously, radiation levels could be reduced to negligible levels with huge amounts of shielding that would be prohibitively expensive and unwieldy. The ALARA concept seeks to strike a reasonable balance between safety and practicality.

RAPHEX Diagnostic Question 2003 D91-92: Match the following maximum permissible fluoroscopic tabletop exposure rate with the type of II exposure control system (under-table x-ray tube): A. 5 mR/min B.10 mR/min C. 5 R/min D. 10 R/min E. No limit D91: Manual control D92: Automatic brightness control

RAPHEX Answer to 2003 Question D91-92 D91: C. 5 R/min With manual control, where the operator sets the mA and the kVp, and it remains at those settings, the federal performance standard limits table top exposure rate to 5 R/min for under-0table x- ray tubes. D92: D. 10 R/min With auto-brightness control systems, the table top exposure rate can be 10 R/min. The philosophy is that in this mode it is allowable to go higher exposure rates for the thick patients.

RAPHEX Diagnostic Question 2003 D93: In 131 I therapy for thyroid cancer, the whole body clearance curve is commonly plotted versus time. The radiation absorbed dose to the patient is proportional to the ____. A. Administered activity of I-131 B. Administered activity per unit body surface area C. Administered activity per unit body weight D. Peak counts in the clearance curve E. Area under the clearance curve normalized to per unit body weight

RAPHEX Answer to 2003 Question D93 E. Area under the clearance curve normalized to per unit body weight. The absorbed dose depends on the patient specific clearance kinetics. The same activity administered to two different patients of the same weight could result in different absorbed doses, if they metabolized and cleared the 131 I at different rates.

RAPHEX Diagnostic Question 2003 D95: Well-collimated AP and lateral chest radiographs are taken on a patient. She later discovers that she was pregnant at the time of the study. The expected fetal radiation dose would be about ___ mSv. A B. 0.5 C. 5 D. 50 E. 100

RAPHEX Answer to 2003 Question D95 A According to HEW 9FDA) the embryo would receive about to of the primary beam. Since AP chest radiographs usually deliver less than 30 mR at the skin surface, and the LAT is about 2.5 times greater, the dose to the fetus would be less than X (30 X 3.5) = 0.42 mR or mGy, which is about

RAPHEX Diagnostic Question 2002 D91: In nuclear medicine studies, critical organ doses are usually about ___ Gy. A B C. 0.5 D. 5 E. 50

RAPHEX Answer to 2002 Question D91 B Gy = 5 rad

RAPHEX Diagnostic Question 2002 D92: The typical amount of lead in lead aprons used in fluoroscopy rooms is about ___. A. 10 um B. 0.1 mm C. 0.5 mm D. 0.5 cm E. 1.0 cm

RAPHEX Answer to 2002 Question D92 C. 0.5 mm 0.5 mm Pb will reduce the x-ray intensity by 95% to 99%, depending on the kVp.

RAPHEX Diagnostic Question 2002 D93: During a typical fluoroscopy procedure a radiologist wearing a lead apron and no protective eyewear receives a uniform whole body exposure of 20 mR. How many similar procedures can the raiologist perform in one week? A. 5 B. 15 C. 50 D.100 E. 250

RAPHEX Answer to 2002 Question D93 B. 15 The NCRP recommended doses are 5 rem/yr to the eyes. This is equivalent to 100 mrem/week whole body and 300 mrem/week to the eyes. Since the lead apron will stop 95 % of the whole body dose, the eye dose is limiting facotr, and will reach 300 mrem after fifteen 20 mR procdures.

RAPHEX Diagnostic Question 2001 Match the exposure with the appropriate exam: A. 15mR B. 30mR C. 60mR D. 5R E. 10R D85: CT head scan ESE D86: Lateral chest ESE

RAPHEX Answer to 2001 Question D85-86 D85: D. 5R 4 to 6 R are typical values for a head scan series D86: C. 60mR A lateral chest ESE is typically 50 to 80 mR.