RADIOPHARMACUTICALS AND RADIATION SAFETY

Question 1

What is the half life of fluorine-18?

Answer 1

110 minutes

Question 2

What is the half life of technetium-99m?

Answer 2

6 hours

Question 3

What is the half-life of thalium-201?

Answer 3

3.04 days

Question 4

What is the half life of cobalt-57?

Answer 4

271.7 days

Question 5

What is the effective half life of a radiopharmacutical and how is it calculated?

Answer 5

The effective half life is the time a radiopharmacutical stays in the body. It is Te and is calculated using the formula 1/Te = 1/Tp + 1/Tb, where Tp is the physical (real) half life and Tb is the biological (in the body) half life.

Question 6

Which radiomuclide is useful for qualiy assurance and calibration of PET scanners?

Answer 6

Germanium-68 is long-lived (half-life = 271 days) and decays to the positron-emitting gallium-68 (half-life = 68 minutes), so a sealed germanium-68/gallium-68 source behaves in effect like a long-lived positron emitter.

Question 7

Can Thalium-201, Technetium-99m, Cobalt-57 and Iodine-131 be used for PET scanners?

Answer 7

No!
These don’t emit positrons and only emit single photons.

Question 8

For a same-day myocardial perfusion study using thallium-201-chloride and technetium-99m-sestamibi, which radiopharmaceutical should be scanned first and why?

Answer 8

We should use Thalium-201 chloride first to minimize scatter contamination.

A main concern for image quality is that a large number of scattered technetium-99m gamma rays are detected in the 70-keV window of thallium-201, and thus, thallium-201 should be imaged first. The technetium-99m half-life is 6 hours, so technetium-99m persists for a same-day study and produces sufficient counts. The order of the studies does not reduce radiation dose.

Question 9

How is Rubidium-82 produced?

Answer 9

Rubidium-82 is the daughter of strontium-82 (half-life = 25 days) and is eluted from a strontium-82/rubidium-82 generator.

Question 10

What method is used to produce Nitrogen-13, Carbon-11 and Fluorine-18?

Answer 10

Cyclotron

Question 11

What is Ultra-tag and how is it used to label RBCs in MUGA scans?

Answer 11

Ultratag has stannous citrate along with acid citrate dextrose and sodium hypochlorite. Labeling RBCs using this pharmaceutical is by in vitro method. One to three milliliters of heparinized blood is added to the vial containing stannous citrate and incubated at room temperature for 5 minutes. During the incubation period, the stannous ion diffuses the RBC membrane after which sodium hypochlorite along with acid citrate dextrose is added to the reaction vial, followed by the addition of 30 to 40 millicuries of sodium pertechnetate-technetium-99m and incubation for another 20 minutes. The pertechnetate-technetium-99m diffuses the RBC membrane and is reduced intercellularly by the stannous ions. Reduced pertechnetate-technetium-99m does not diffuse out of the RBC. Typical labeling efficiency is >97%.

Question 12

Limitation of using Sn-Pyrophate for labelling in MUGA scans in patients on heparin?

Answer 12

Heparin is one of the drugs that inhibit the diffusion of stannous ion to the RBC with the use of Sn-Pyrophate, and the labeling is compromised in that some of technetium-99m-pertechnetate is reduced

Question 13

What is the half value layer (HVL) of a material?

Answer 13

The HVL is the amount of thickness of a material needed to reduce the exposure to half.

If HVL of lead is 0.3mm then to reduce exposure from 5 -mR to 0.7 mR; One layer will reduce to 2.5 mR. Two layers will reduce to 1.25 mR. Three layers will reduce to 0.625 mR. So three HVLs will be needed.

Question 14

What must be under the control of NRC (Nuclear regulatory commision) regulations when it comes to possession of a radioactive material?

Answer 14

1. Disposal of the radioactive material
2. Use of the radioactive material.
3. Limits/amount of radioactive material possessed at any given time

Note: Cost of the radioactive material are not controlled by the NRC regulations.

Question 15

What are unrestricted areas?

Answer 15

Unrestricted areas are those areas to which access is neither limited nor controlled by the licensee

Question 16

What are restricted areas?

Answer 16

Restricted areas are those to which access is limited by the licensee for the purpose of protecting individuals against unnecessary risks from exposure to radiation and radioactive materials. Usually, the hot lab, imaging room(s), and thyroid uptake room are considered restricted areas.

Question 17

In an unrestricted are of a nuclear imaging facility do we require any signs to be posted?

Answer 17

Areas not under the control of the licensee and areas where a person receives <2 mrem per hour do not require posting.

Note: Radioactive signs are not required where radioactive materials are handled for <8 hours and are under constant observation, and in rooms where sealed sources are stored and the exposure doesn’t exceed 5 mrem per hour at 1 m.

Question 18

Caution: Very High Radiation Area sign should be posted in an area where radiation exceeds?

Answer 18

NRC regulation states that when an individual could receive a dose > 500 rads per hour at 1 m from the source, the area should have the Caution: High Radiation Area sign posted

Question 19

Transportation index found on radioactive shipment packages is a measurement of?

Answer 19

The transportation index of a package having radioactive materials is to be measured at a distance of 1 m from the surface. It is a measurement of exposure measurement at 1m from the surface of the package.

Question 20

What is the best detector for measuring radiation on a radioactive package (removable contamination) ?

Answer 20

The well counter is the most sensitive and practical for measuring the swipes that are used to test packages delivered to a nuclear laboratory. It is a solid scintillation counter and is very sensitive to low levels of radioactivity.

Question 21

What is a dose calibrator used for?

Answer 21

The dose calibrator is used routinely to measure radiotracer doses prior to being injected into the patient.

Question 22

Restrictions prior to pharm stress test?

Answer 22

Caffeine abstention is required for 12 to 24 hours when patients are scheduled to undergo dipyridamole, adenosine, or regadenoson pharmacologic stress. Caffeine may interfere with the vasodilatory effects of these drugs and lower overall accuracy by decreasing sensitivity. Beta-blockers and nitrates taken prior to stress will decrease the detection of ischemia. They should be held 12 to 24 hours prior to testing.

These restrictions are not required if patient is undergoing exercise stress test.

Question 23

Thalium-201 in breast feeding patients?

Answer 23

Thallium-201 will contaminate breast milk and, due to the 72-hour half-life, will expose the infant to unnecessary radiation. Radionuclide stress testing in such patients should be delayed if possible until the patient stops breast-feeding or alternative methods of testing are considered. If patient undergoes a Thalium-201 stufy they should discontinue breast-feeding for 2 weeks after the test.

Question 24

What is the best monitoring device for the measurement of occupational dose for a radiation worker?

Answer 24

Photographic film badges consist of a holder and a radiation-sensitive film. They are used for monitoring cumulative whole-body exposure to ionizing radiation. They record both high and low radiation levels and are generally worn on the torso outside of clothing. In some circumstances, they may be worn underneath a protective lead shield to record the actual exposure to critical organs.

Question 25

What does thermoluminescent ring badge measure?

Answer 25

Thermoluminescent ring badges are used to measure the amount of exposure received by the hands and consist of an inorganic crystal held in a hand ring device.

Note: A survey meter and Geiger counter are handheld devices used to measure contamination.

Question 26

NRC annual body radiation expsoure limit for a radiation is?

Answer 26

The NRC limits a radiation occupational worker to receive a total whole-body dose of 5 rem per year OR 1.25 rem per quarter year. . It is measured in quarterly intervals so that individuals getting high rates can be identified and corrective actions taken to limit further exposure in order to avoid exceeding the yearly total. Specific organ limits include 15 rems to the eyes and 50 rems to the extremities.

Question 27

Which radioactive materials can be released into the sewer system?

Answer 27

Unused radioactive patient doses, contaminated materials such as paper towels to clean a spill should not be released in to the sewer system and should be allowed to decay for 10 half lives and then disposed off like non radioactive materials.

Sealed radioactive sources usually take a long time to decay and should not be released.

Patient urine and feces can be released in to the sewer system

Question 28

How frequently should survey radioactive materials areas as per the NRC?

Answer 28

In accordance with the ALARA (as low as reasonable achievable) principles, the NRC requires that daily surveys be performed with a survey instrument at the end of each day. Less frequent surveys would fail to detect unsafe radiation use practices that may result in unnecessary radiation exposure to patients, staff, or the public. Documentation that such surveys were performed is necessary.

Question 29

Radioactive contamination of the skin is best removed by?

Answer 29

Washing with luke warm water and soap.
Note: Hot water opens the skin pores and makes absorption worse.

Question 30

The maximum exposure amount allowed by the NRC to a fetus of a pregnant occupational worker is?

Answer 30

The dose to the embryo/fetus shall not exceed more than 500 mrem from occupational exposure for a declared pregnant worker. To monitor this occupational dose, a separate radiation film badge is issued and worn on the fetal area. Pregnant employees need to be counseled on appropriate radiation safety measures and duties without radiation exposure considered. The risks to the fetus are highest during the first trimester.

500 mrem for the entire pregnancy

Question 31

Radiation amount can be reduced by what factors?

Answer 31

1. Total time of exposure: More time more exposure
2. Distance: Greater the distance lesser the exposure
3. Shielding: highest possible density material reduces radiation exposure by the process of attenuation; for gamma radiation, higher atomic number materials should be used.

Question 32

What labeling categories are used by Department of Transportation and NRC for radioactive materials?

Answer 32

The DOT and the NRC have set limits on the amount of radiation that can be detected at the surface and at 1 m from a package containing radioactivity. The categories are listed in Table 2-1. The labeling category will determine the shielding requirements.

Example: A package containing radioactive material is received in the hot lab and found to have a radiation exposure of 5 mR/h at the surface and 0.2 mR/h at 1 m from the surface would be Yellow II even though at 1m it is only 0.2 and not greater than 1.

Question 33

How long after a technetium-99m rest or stress injection should we acquire images?

Answer 33

30-60 minutes

The time delay after injection of a technetium-99m perfusion agent is to allow clearance from the liver and maximize the myocardial uptake. Immediately and 15 minutes after a resting or pharmacologic stress injection, there is too much liver activity present to see the inferior wall of the heart without contamination. At 30 to 60 minutes, there is adequate liver clearance to visualize the inferior wall. By 2 hours, the liver will have cleared, but there is a greater probability of having loops of bowel adjacent to the heart and there is greater decay of the radioactivity in the heart.

The rest imaging can be started 30 to 60 minutes postinjection, and the stress imaging started 10 to 20 minutes after exercise stress and 30 to 60 after pharmacologic stress.

Question 34

What is the stress and rest dosages of Technitium-99?

Answer 34

The rest dose should be approximately one-third the stress dose with some variation introduced by the length of time between the two studies. If the interval between studies is short, the stress requires a higher dose, and if it is long, the full three times greater dose may not be needed due to decay of the resting injection. With 1:3 dosing, the higher stress dose overcomes the smaller rest dose so that the stress images have less residual activity from the rest study. If the rest dose is high, the stress dose will need to be three times higher, and this will give the patient an unacceptably high level of radiation. If a lower dose is used for stress without enough time between the injections, there will be residual activity from the rest study that can underestimate the amount of ischemia present.

Dose range for rest is usually: 8 to 12 mCi

Question 35

Technetium-99m labeled perfusion tracers have better SPECT perfusion imaging relative to Thalium 201 due to?

Answer 35

Technetium-99m–labeled agents have improved SPECT imaging characteristics compared to thallium-201 due to the higher photon energy (140 KeV vs. 60–80 KeV), which has less total attenuation and the shorter half-life (6 hours vs. 72 hours) allowing administration of a much higher dose but less total body radiation.

Question 36

How is the extraction fraction of Technetium-99m and Thalium-201?

Answer 36

The extraction fraction across the coronary bed is actually lower for both technetium-99m agents in comparison to thallium-201, and this raised theoretical concerns regarding lower sensitivity for technetium-99m during the much higher coronary flow rates achieved with vasodilator pharmacologic stress.

Question 37

How is attenuation correction performed?

Answer 37

Various methods have been utilized for attenuation correction including a radioactive line source (gadolinium) and x-ray–based techniques (computed tomography). Both methods create a patient-specific tissue attenuation map that is used to correct for the loss of counts due to differences in the amount and type of tissue between the heart and the detector. Attenuation correction remains a vendor-specific tool with no uniform standards established by industry or professional medical societies. When applied correctly, attenuation correction reduces soft tissue–related defects and specificity increases, so fewer studies are read as abnormal due to attenuation that may frequently be misinterpreted as a prior infarction.

Question 38

What is the maximum permissible activity concentration of molybdenum-99 to technetium 99m as stipulated by NRC?

Answer 38

0.15 μCi/mCi at the time of administration to the patient.

Question 39

Is the Aluminum ion concentration is Technitium-99m regulated by the NRC?

Answer 39

No

Question 40

What are the limits of Aluminum ion in Technetium-99m?

Answer 40

Al ions limits are recommended by United States Pharmacopeia (USP-XXIII)—Limits are 10 μg/mL of eluate.

Question 41

When a radioactivity package is delivered to the hot lab of a nuclear medicine department, when must the package be monitored for radioactive contamination?

Answer 41

The licensee shall perform the monitoring required as soon as practical after receipt of the package, but not later than 3 hours after the package is received at the licensee’s facility if it is received during the licensee’s normal working hours, or not later than 3 hours from the beginning of the next working day if it is received after working hours.

Within 3 hours after receiving in the hot lab or within 3 hours from the beginning of the next working day, if received after working hours.

Question 42

How should technenium-99m radioactive waste generated in a nuclear medicine department be disposed?

Answer 42

Store in-house for decay to background radiation level before disposal.

A licensee may hold by-product material with a physical half-life of less than or equal to 120 days for decay-in-storage before disposal without regard to its radioactivity. The lab should monitor by-product material at the surface before disposal and determines that its radioactivity cannot be distinguished from the background radiation level with an appropriate radiation detection survey meter set on its most sensitive scale and with no interposed shielding.

Question 43

Members of the public in the United States are subject to ionization radiation exposure from natural and man-made radiation sources. On average, they receive approximately half from natural occurring and the other half from man-made, predominantly medical, sources. How much is received annually from all sources?

Answer 43

NCRP (National Council on Radiation Protection)

NCRP report 160 emphasized that the average exposure to members of public in the United States has increased from 360 mrem (3.6 mSv) in 1980s to 620 mrem (6.2 mSv) in 2006. This increase is from medical uses of radiation from nuclear medicine and x-ray, predominately from diagnostic CT.