Personal Protection: Source Shielding :Personal Protection: Source Shielding By: Karina Caboverde, Jorge Artamendi, Daniel Ferro


Occupational Exposure- Protection of the Worker :Occupational Exposure- Protection of the Worker Licensees shall ensure for all workers that: occupational exposure be limited and optimized suitable and adequate facilities, equipment and services for protection be provided appropriate protective devices and monitoring equipment be provided and properly used appropriate training be provided as well as periodic retraining and updating


PET Exposure factors- F18 :PET Exposure factors- F18 Half life is 110 minutes Major radiation emission: 511 keV (gammas) Half value layer: 4.1 mm for Pb and 3.5 cm for concrete- this is for narrow beam conditions Use of these values will not provide sufficient shielding; they neglect scatter buildup factors


F-18 FDG Pet studies :F-18 FDG Pet studies


F-18 FDG PET :F-18 FDG PET Patient preparation rooms are a requirement for any PET facility, and must include radiation safety planning. Survey Meters Decontamination Kits


Objectives :Objectives Exposure rate factors Discuss Exposure factors on F-18 FDG Discuss dose factors for F-18 FDG Explain source shielding and identify shield resources Explain structural shielding and their proper calculations


PET Exposure factors F-18 FDG :PET Exposure factors F-18 FDG Calculated gamma constant:0.57 R m²/mCi hr Dose Rate Constant: 0.55 rem m²/mCi hr SI: 0.147 mSv/ MBq hr at 1 meter Workload for scanner room: 8-16 pts/day x 5 days/wks= 40-80 pts/wk


Dose Factors F-18 FDG :Dose Factors F-18 FDG Dose Rate constant: F- 18: 0.188 uGy m²/ MBq hr resulting in a dose rate associated with 37 MBq (1 mCi) of F-18 is 6.96 uGy/hr at 1 meter from an unshielded point source The dose rate of the patient is reduced by a factor of 2 or more due to the body absorbing some of the annihilation radiation The mean maximum value reported at 1 meter from the patient just after administration is 3.0 uGy/hr/37MBq


Other PET Isotope Data :Other PET Isotope Data N-13: Half life = 10 minutes O-15: Half life = 2.07 minutes C-11: Half life = 20.4 minutes Rb-82: Half life = 1.3 minutes Ga-68: Half life = 68.3 minutes These isotopes are dominated by the F-18 requirements


Exposure :Exposure Annual exposure to occupationally exposed individuals working in adjoining rooms (without shielding) is expected to be less than 5 mSv even for a busy PET tomography. Staff that works directly with PET patients receive largest doses: Exposure from patient injections Exposure from patient positioning Exposure during imaging


Shields used :Shields used Bench top shield Vial shields Syringe shields Structural shielding


Shielding of Sources :Shielding of Sources Factors affecting the design of shield: Radionuclide used Activity of source Shielding Material


Shielding Material :Shielding Material Transmission in Lead: Transmission is lower than constant TVL


Transmission in Concrete :Transmission in Concrete Transmission is lower than constant TVL


Transmission in Steel :Transmission in Steel Transmission is lower than constant TVL


Bench Top Shielding :Bench Top Shielding Gamma radiation (lead) Lead acrylic With low energy gamma emitters Not recommended for Beta emitters Ideally used in: Hoods Laboratory benches Any “hot” area where local shielding is needed 10mm acrylic shield: gives maximum beta radiation protection with an efficiency level over 99.9% when using isotopes such as P32 or Strontium 89.


Syringe Shield :Syringe Shield Syringes containing byproduct materials should be administered with a radiation shield Each syringe and syringe radiation shield should be properly labeled when containing a radiopharmaceutical for proper identification. Label must have full name and abbreviation of radiopharmaceutical. Anyone who is preparing a radiopharmaceutical kit, must use a syringe radiation shield, and do the same when administering to the patient.


Vial Shields :Vial Shields When preparing or handling a vial with radiopharmaceuticals, vial must be maintained in a vial radiation shield In order to identify the vials contents, the vial and vial radiation shield should be properly labeled with the radiopharmaceuticals full name and abbreviation.


Structural Shielding :Structural Shielding The absorbed dose is determined by factors such as: source strength length of exposure distance from the source transmission through the protective barrier. Radioactive Patient Ordinary patient Distance


PET Clinic Layout :PET Clinic Layout Quiet Rooms PET/CT Patient Bathroom Hot Lab PET/CT Control


PET Clinic Layout :PET Clinic Layout Some clinic layouts utilizes distance rather than shielding to protect the technologist. The quiet areas are >20 feet distant from the tech at the PET/CT control.


Typical PET room layout :Typical PET room layout Notice the distance of the “HOT” areas and regular rooms in order to control exposure


Distances to be used in shielding calculations :Distances to be used in shielding calculations


Distances to be used in shielding calculations :Distances to be used in shielding calculations It should be kept in mind that it may be necessary to shield the vertical barriers all the way from the floor to the barrier above (instead of the 7 feet height usually required for x-ray installations). The vertical barrier need not have the same thickness over its entire height since the rays from the patient will traverse the higher portions of the vertical barrier obliquely and therefore pass through a greater thickness of shielding material.


Calculation for Room Above an Uptake Room - Example :Calculation for Room Above an Uptake Room - Example What is the weekly dose equivalent to a room above an uptake room? Patients are administered 555 MBq (15 mCi) of F-18 FDG, the uptake time is 1 hour and there are 40 patients per week. The floor to floor distance is 4.3 meters and there is 10 cm of concrete between floors. D = (4.3 – 1) + 0.5 = 3.8 meters Shielding factor for 10 cm of concrete is 2.5 (3 uSv/37 MBq x 555 MBq x 40 x 1/3.82)/2.5 = 48.3uSv/week 20 uSv/48.3 uSv = 0.41 = 1.3 HVL Using NCRP values, this requires 0.65 cm of lead or 6.8 cm of concrete.


PET Clinic Shielding :PET Clinic Shielding Inadequate structural shielding in some facilities has led to high doses to non-occupationally exposed personnel both within the facility and adjacent to it. Improper hot lab shielding has led to high doses to the Nuclear Medicine technologists E.g. “L” block and syringe shields


Wall Shielding :Wall Shielding Wall shielding is commonly required for the hot lab, quiet rooms, and scanner room. Many designs use distance rather than shielding for the interior spaces as technologists dislike closing off their patients in the quiet rooms. Doors, when provided, are rarely closed.


Summary :Summary Exposure rate factors Discuss Exposure factors on F-18 FDG Discuss dose factors for F-18 FDG Explain source shielding and identify shield resources Explain structural shielding and their proper calculations


Question 1 :Question 1 F-18 FDG is a nonspecific tracer for metabolic activities, Which organs is it normally in?


Answer 1 :Answer 1 Brain Kidneys Bowels Heart Bone marrow Activated muscles


Question 2 :Question 2 What is the result if we double to distance of a source?


Answer 2 :Answer 2 It reduces the intensity by 2 square


Question 3 :Question 3 What must each PET facility patient preparation room include?


Answer 3 :Answer 3 Radiation safety planning which includes survey meters and decontaminating kits


Question 4 :Question 4 How can the staff that works directly with PET patients, receive large radiation doses?


Answer 4 :Answer 4 Exposure from patient injections Exposure from patient positioning Exposure during imaging


Question 5 :Question 5 What type of shields are used in a PET facility?


Answer 5 :Answer 5 Bench top shield Vial shields Syringe shields Structural shielding


Question 6 :Question 6 When should a syringe shield be used?


Answer 6 :Answer 6 When preparing a radiopharmaceutical kit and administering dose to the patient.


Question 7 :Question 7 What are the factors that determine the absorbed dose?


Answer 7 :Answer 7 Source strength Length of exposure Distance from the source Transmission through the protective barrier


Question 8 :Question 8 Where is wall shielding commonly required?


Answer 8 :Answer 8 “HOT” lab rooms, quiet rooms, and scanner rooms


Question 9 :Question 9 When clinics use distance rather than shielding to protect the technologist, what is the distance they utilize?


Answer 9 :Answer 9 The quiet rooms are >20 feet distant from the PET/CT control rooms in order to protect the technologist


Question 10 :Question 10 What radioisotopes is lead acrylic used with, and which are not.


Answer 10 :Answer 10 Used with low energy gamma emitters Not recommended for Beta emitters


Resources :Resources Christian Waterstram-Rich. (2007).Nuclear Medicine and Pet/CT. St. Louis, Mo. Dale L. Bailey. (2008).Positron Emission Tomography-Basic Science. Published 2005, Springer. Peter E. Valk, Dale L. Bailey, David W. Townsend, Michael N. Maisey . (2008). Positron Emission Tomography-Basic Science and Clinical Practice.Published 2003, Springer