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Radiation Safety for PET

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Information about Radiation Safety for PET
Education

Published on April 21, 2010

Author: seymoh

Source: authorstream.com

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Radiation Safety consideration for PET/CT : Radiation Safety consideration for PET/CT By Seyed Mohammadi Slide 2: Program Objectives 1)Explain the basic physics concepts pertinent to PET radiation safety; 2)List the key variables associated with dose exposure in a PET facility and give examples of actions to affect these variables; 3)List the factors related to dose exposure and give examples for reducing exposure for each factor; 4)List the NRC components for a radiation safety program; name the basic elements of the radiation protection program; 5)List the individual employee radiation safety responsibilities and general safety measures that all workers should follow; 6)Identify the parameters in each ALARA level and the actions associated with exceeding each parameter and discuss the specifics regarding a declared pregnancy; 7)List the actions taken in decontamination of accidental radiation exposure including personnel contamination; 8)List the actions specific to area and facility monitoring including material receipt and radioactive material package opening; 9)Name the specific records that regulations require a facility to keep for three years, five years, and the life of the facility license; 10)Describe the proper waste disposal procedure in a PET facility; and define misadministration and recordable event and summarize the required actions related to a recordable event. Why we have radiation protection Program : Why we have radiation protection Program December 1895: Roentgen discovers x-rays, 1/1896 - 12/1896: 23 cases of radiation dermatitis documented. 1911 -1914: 252 radiation-induced cancer cases with 54 fatalities. Slide 4:  Slide 5:  Slide 6: Federal Regulations, Part 28 "10 CFR 35" - Title 10, Code of Federal Regulations, Part 35 10 CFR 20 addresses general standards for radiation protection, 10 CFR 35 addresses use of "by-product" materials in medicine. NRC directly oversees 16 states. 33 "Agreement States" implement NRC regulations—and then some, FDA regulates production of PET radiopharmaceuticals, and manufacture and sale of CT scanners, individual states regulate operation of CT scanners. International Commission on Radiological Protection (ICRP) Slide 7: High Energy Gammas Positron Emission Tomography, PET radiopharmaceuticals have higher Energy gammas than the radiopharmaceuticals used in conventional nuclear medicine facilities. These higher energy gammas are harder to shield and are a source of increased exposure. Fluorine-18 is the isotope used in the production of Fluorodeoxyglucose (FDG), the most commonly used radiopharmaceutical in PET imaging. Look at this comparison between the higher energy photons of Fluorine-18 (F-18) and the photons of Iodine-131 and Technetium-99m, both of which are used in conventional nuclear medicine. Note the significantly higher energy from Fluorine-18 photons than from the Iodine-131 photons, which is usually the highest energy radiopharmaceutical used in nuclear medicine. Slide 8: AS LOW AS Reasonably Achievable Slide 9: Annual Radiation Dose Limits Slide 10: Cyclotron Hot Lab PET CT Scanner Radiation Warning Sings Slide 11: CT Scanner PET Scanner + = TWICE the Headaches Slide 12: Record Retention Shipping and Receiving (3 years) Area Surveys and Trash Surveys (3 years) Public Dose Limit Compliance {3 years) Personnel Dosimetry (lifetime) 10CFR20: Personnel monitoring occupational dose is required if the sum of external and internal EDE could be expected to exceed 10 % of the annual whole -body occupational limit. Licensees can monitor at low er exposure levels as part of an ALARA Slide 13: Why is PET different? Exposure Rate Constant: The exposure rate constant (ERC) of a radionuclide is the exposure rate (in Roentgen per hour) at 1 centimeter from a 1-millicurie source. The ERC for PET radiopharmaceuticals is higher than the exposure rate constant for more conventional nuclear medicine radiopharmaceuticals. This can result in higher radiation dose exposure for PET facility employees. The ERC for FDG is 5.7 R/hr/mCi. If we compare FDG to Technetium-99m, we see that the ERC is about 0.6 R/hr/mCi which is about 1/10 that of the FDGs. This means that for two (2) doses of the same activity, the F-18 dose would give off 8 -10 times more radioactivity than the Technetium-99m. Also, you will notice that the ERC for Fluorine -18 is 2.6 times higher than the Iodine-131, which is 2.18 R/hr/mCi. The concept of exposure rate constant can be used to generate equivalent activities for Fluorine-18, Technetium-99m and Iodine-131 that give the same dose rates in air. An 18 mCi dose of FDG would give off the same radiation exposure as a 180 mCi bulk Technetium-99m dose or a 47 mCi therapy dose of Iodine-131. This means that FDG doses give off much more radiation than the typical Technetium-99m doses used in general nuclear medicine Slide 14: PET radionuclides have higher Exposure Rate Constants than "traditional" nuclear medicine radionuclides. Photon energies are higher. Half-lives are shorter. Why is PET different? Exposure Rate Constant Slide 15: Higher Exposure Rate Constants Slide 16: Higher Dose Rate From Patients Slide 17: PET Shielding: Tenth Value Layers Slide 18: Half-value Layer Half-value layer is a convenient way to express the attenuation properties of a material for photons. Half-value layer is defined as the amount of material needed to reduce the intensity of a radiation source to one half of its original intensity. This value is normally expressed as thickness. The half-value layer for FDG in lead is 3.85mm. The half-value layer for Technetium-99m in lead is 0.3mm. The half-value layer for Iodine-131 in lead is 3mm. We know the 511 keV photons in FDG require more shielding; lead is not sufficient. Tungsten is the material most commonly used in shielding FDG for several reasons. First, it has a density of 19.3 g/cm^3 compared with 11.35 g/cm^3 for lead. This high density provides greater radiation attenuation while allowing a reduction in overall size and weight of the shield. Tungsten also has a high rigidity modulus; this allows for the manufacturing of direct threaded closures. And, finally, its tensile strength, comparable with steel, allows it to withstand everyday use Slide 19: Positrons can be stopped by 2 - 5 mm Lucite. Gammas require a high-Z material. Neutrons require high hydrogen content (paraffin or the "waters of hydration" in concrete). Slide 20: Material Tenth Value Layer in cm PET Barrier Material Slide 21: X-ray Aprons — No Protection at 511 ac I 0,5 mm lead equivalent. These afford significant protection at energies under 120 KeV, but are nearly useless against annihilation photons. 100 KeV: Transmission = 4.3% 511 KeV: Transmission = 91.0 % Slide 22: Optimize administered radioactivity, Reduce CT mAs. Increase "pitch". « Technique charts to minimize CT exposure to pediatric patients and small adults. Reducing PET/CT Patient Dose Rgf: Beyer T,Mullerr SP. Brix G et aS. Radiation exposure during combined whoie-body FGD-PET/CT imaging. 51S! Annual Meeting. Society of Nuciear Medicine, Jun 22, 2004 Abstract 1331, Slide 23: Shorter Physical Half-Life Slide 24: Shorter Half-Life » Lower Dose 'Dose received by a bystander at 1 meter during 5 half-lives or more Slide 25: Cyclotron (?) Radiopharmaceutical Production (?) Dose Dispensing / Calibration Dose Administration Patients X-rays From CT PET/CT: Sources of Exposure to staff Slide 26: What Doses Do People Get? Ref: Beyer T. Mueller SP, Brix G et at. Radiation exposure during combined whole-body FGD-PET/CT imaging. 51-l Annual Meeting, Society of Nuclear Medicine, June 22, 2004 Abstract 1331. Slide 27: Time, and Shielding Laboratory Technique Administrative and Procedural Controls Measures to Reduce Personal Dose Slide 28:  Slide 29: inverse Square Law (l/r2) Dramatic reductions in exposure Simulations of PET technologist's interactions with patients show that 75% of dose is accumulated during time tech is within 2 meters of patient. Maximize Distance Slide 30: Positrons Positron energy dictates travel distance. Half-life is the amount of time required for a radioactive isotope to lose half of its radioactivity through the process of decay. Fluorine-18 is a good choice for PET imaging. First, it has a longer half-life than most other positron emitters, so it can be shipped. Without this characteristic, an in-house cyclotron would be needed to produce the pharmaceuticals. Also, its lower energy positron means it travels less distance in the body before an annihilation event, which improves spatial resolution when imagining. From a safety standpoint, the positron from F-18 has a range of about 1.8 meters in air, if contained. If there is a spill, the spill should be covered, if possible, to contain the positrons and minimize contamination. When FDG is contained in a vial or syringe, the positrons are basically contained. Slide 31: Half-value Layer Half-value layer is a convenient way to express the attenuation properties of a material for photons. Half-value layer is defined as the amount of material needed to reduce the intensity of a radiation source to one half of its original intensity. This value is normally expressed as thickness. The half-value layer for FDG in lead is 3.85mm. The half-value layer for Technetium-99m in lead is 0.3mm. The half-value layer for Iodine-131 in lead is 3mm. We know the 511 keV photons in FDG require more shielding; lead is not sufficient. Tungsten is the material most commonly used in shielding FDG for several reasons. First, it has a density of 19.3 g/cm^3 compared with 11.35 g/cm^3 for lead. This high density provides greater radiation attenuation while allowing a reduction in overall size and weight of the shield. Tungsten also has a high rigidity modulus; this allows for the manufacturing of direct threaded closures. And, finally, its tensile strength, comparable with steel, allows it to withstand everyday use Slide 32: Distance There are three key variables associated with radiation dose exposure in a PET facility: distance, time, and shielding. The first key variable is distance. Radiation has an inverse square relation with distance. If the distance from a radiation source is doubled, the exposure rate will be reduced by 75%. The majority of the radiation dose a PET technologist receives is from being near the patient. Note these comparison figures of typical dose rates at tableside for FDG and Technetium-99m. In general, PET technologists receive about twice the dose of general nuclear medicine technologists. Tableside exposure can be as much as ten times higher. Actual personnel exposures are not 10 times higher because of the radiation safety precautions that are taken with PET imaging. The simple practice of taking a step or two away from the patient whenever possible will significantly reduce your radiation dose. Slide 33: Time The second key variable is time. Time can be influenced by study protocol, obtaining and maintaining an IV, transport of a patient, and dose preparation. A number of strategies can be used to reduce the time variable. Practice detailed, complete dry runs to improve time efficiency. Schedule patient instructions and patient question time prior to dosing, if possible. Time spent next to the patient contributes to 30%-80% of staff dose results. Minimizing the amount of time that staff spends with the patient will reduce the radiation dose.Rotation of staff is an effective method of limiting dose exposure. Careful consideration of the various duties and responsibilities of all staff should be made when assigning workloads to be sure that radiation exposure is distributed among staff as evenly as possible. Slide 34: Technologists should minimize the time spent in close proximity (less than two meters) from the patient. Slide 35: Shielding The third key variable, shielding, is especially critical in PET because of the higher energy gammas in PET pharmaceuticals. In the hot lab, it is most effective to shield the source, not the walls. Unit doses should be kept in shielding at all times except during preparation and assay. Staff should utilize tungsten pigs and syringe shields to reduce exposure to hands and fingers, and L-shields and lead bricks to reduce exposure as they remove the dose from behind the L-shield to the dose calibrator. Two inches of lead are required for shielding the dose calibrator for PET. Mobile shielding is also known as shadow shields. This is because it casts a shadow in the area of which the radiation is shielded. This can be useful for reducing radiation levels from injected patients in waiting rooms. In some rooms lead shielding in the walls may be used to reduce radiation levels in surrounding areas. Slide 36: Imaging Device Additional factors that affect the exposure dose rate include the imaging device, the study protocol, personnel workload, dose preparation, injection technique, and facility design. The imaging device used is a major factor in staff and patient dose. There are three basic units available: dedicated PET unit, dedicated PET/CT, and a Nal coincidence camera. NaI coincidence cameras use doses between 3 and 5 mCi. However , dedicated PET and combination PET/CT scanners use doses between 10 and 20 mCi, about 2-6 times higher than the Nal camera. This dosage increase results in increased exposure dose to both the technologist and the patient. Slide 37: Study Protocol The study protocol determines the amount of the dose administered to the patient and the dose at imaging. This also affects the radiation dose technologists will receive. The study protocol also affects the key variable of time. The longer the uptake, the less radiation the patients will emit when they are escorted from the waiting room to the scan room. The longer the scan duration, the less radiation the patients will emit when the technologist helps them off the table and escorts them out of the scan room. Note these typical uptake times and study duration times for brain and oncology studies. With any protocol, it is important to provide adequate hydration and have the patient void before the scan. Thirty percent (30%) of the total FDG given to the patient is voided via the bladder. Twenty percent (20%) of the total activity is voided in the first two hours. This practice will reduce exposure to technologists, the patient, and the staff. It will also reduce the number of randoms in the scan. Slide 38: Workload The workload in a PET facility is directly related to staff exposure dose. PET/CT units tend to have higher workloads due to the shorter times needed to acquire the transmission data of the scan. Higher workload has the potential to increase individual dose exposure. The number of employees also affects individual staff workload in a PET facility. If there are more employees, the workload can be divided between more people and thus reduce individual exposure. Slide 39: Dose Preparation Dose preparation is another area where the staff needs to follow protocol that reduces dose exposure. Although, for PET imaging, unit doses are usually used which reduce preparation time, the dose still needs to be assayed, and safety precautions need to be followed. An important item in the hot lab where doses are prepared is the dose calibrator. This instrument detects and measures radioactivity in vials, syringes, capsules, etc. The dose calibrator is usually placed behind a lead or glass-lead shield to minimize exposure. Patient doses and shielded vials are also generally stored behind this shield. If direct measure is used rather than unit dosage, the licensee must have and use specific dose calibrators designed to measure the activity of the unsealed by-product material prior to use. These dose calibrators must be calibrated and records must be kept. Only personnel trained in the proper function of these dose calibrators may use these instruments. Slide 40: Unit doses are those dosages that are prepared for medical use as a single dose. They do not require additional manipulation after initial preparation. The amount of activity is determined by direct measurement or decay correction based on the activity provided by the appropriately licensed manufacturer or other approved preparer. The authorized use physician (AU) will establish the policy for the prescribed dosage or range. It should be noted that if unit doses are from a commercial radiopharmacy, regulations might not require staff to assay the dose before the medical use. Please consult the applicable regulations to verify if a dose must be assayed prior to administration. However, most facilities choose to use a dose calibrator to assay the dose prior to administration, regardless of Slide 41: Facility Design Facility design is crucial: it plays a role in radioactive isotope receipt and storage and in dose preparation and dose assay, all points that affect the radiation dose exposure rate of PET professionals and technologists. A PET center should be designed to give direct (shortest) route from the hot lab to the injection area and from the injection area to the waiting area. It should also have a direct route from the waiting area to the scan room—the restroom should be along this path. The facility should also have a direct route from the scan room to patient release. The control room should always be placed at the foot of the bed to maximize distance between the technologist in the control room and the patient.

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