Discussion topic:
Choose one of the following concepts: time, distance or shielding and give an example of a situation in which the time, distance or shielding is beneficial in limiting dose. Explain the concept behind the example that you choose to give. Note: If someone in your group has already posted a concept try to choose a new concept to present (e.g., if time and distance are already discussed more frequently then choose shielding). Read other posts within your group and post 2 comments, one comment for each of the concepts that you did not choose to explain.
Discussion post:
The three key principals of radiation safety are time, distance, and shielding. Of these three topics shielding might be considered the most complex. Time and distance are relatively straight forward. More distance and less time equate to less radiation exposure. However, shielding depends of several factors and can involve more variables. Radiation type and energy must be considered. The amount of shielding material depends on the type of material. Depending on the designation of the area the amount of shielding required may vary. A brief look at all of these factors will better explain the concept of shielding.
The energy and type of radiation can affect the amount of shielding required. Without considering other variables, it is important to be aware that higher energy 10MV or greater can result in the production of neutrons. Khan1 states that the concrete that surrounds most radiation vaults is sufficient to protect against neutrons but the treatment room door requires special consideration. Hydrogenous materials such as polyethylene. Modern Linear accelerators are capable of producing increasingly higher energy beams. With increase in beam energy comes an increase in shielding needs and special considerations for neutron contamination.1
Another factor to consider in shielding is the type of barrier material used. The value tenth value thickness (TVL) is used to represent the amount of material needed to reduce exposure by 1/10th.1 The TVL for lead is less than steel, which both have a lower TVL than concrete. In some cases, different combinations of lead, steel, or concrete can be used to meet the architectural limitations of a structure. If there is ample room a thick concrete wall can be used for all treatment room barriers. However, if space is limited it may be necessary to use lead or steel which do not have to be as thick to provide the same level of protection.1
The designation of a treatment area is important when considering shielding. Areas surrounding a radiation treatment area are divided into two groups: controlled, and non-controlled.1 Controlled areas must be under supervision of a radiation safety officer and the maximum dose equivalent allowed for the area is .01 mSV/week. Non-controlled areas have a maximum allowance of .02 msv/week.2 Other shielding factors to consider are whether a wall is a primary barrier that protects from the primary radiation beam or a secondary barrier that protects from scatter or leakage radiation.1,2
All of the variables to consider in radiation shielding make it a complex topic. Time, distance, and shielding are the keys to radiation protection and these three factors combined are important in the subject of radiation safety. While the basics of time and distance may be conveyed in a simple and concise manner the topic of shielding is more involved and requires much consideration.
References
1.Khan FM, Gibbons JP. Radiation protection. The Physics of Radiation Therapy. Fifth Edition. Philadephia, PA: Lippincott Williams & Wilkins; 2014:348-360.
2.Casey Abing. Area Monitoring. Lecture presented: University of Wisconsin La Crosse; October 24, 2016
Choose one of the following concepts: time, distance or shielding and give an example of a situation in which the time, distance or shielding is beneficial in limiting dose. Explain the concept behind the example that you choose to give. Note: If someone in your group has already posted a concept try to choose a new concept to present (e.g., if time and distance are already discussed more frequently then choose shielding). Read other posts within your group and post 2 comments, one comment for each of the concepts that you did not choose to explain.
Discussion post:
The three key principals of radiation safety are time, distance, and shielding. Of these three topics shielding might be considered the most complex. Time and distance are relatively straight forward. More distance and less time equate to less radiation exposure. However, shielding depends of several factors and can involve more variables. Radiation type and energy must be considered. The amount of shielding material depends on the type of material. Depending on the designation of the area the amount of shielding required may vary. A brief look at all of these factors will better explain the concept of shielding.
The energy and type of radiation can affect the amount of shielding required. Without considering other variables, it is important to be aware that higher energy 10MV or greater can result in the production of neutrons. Khan1 states that the concrete that surrounds most radiation vaults is sufficient to protect against neutrons but the treatment room door requires special consideration. Hydrogenous materials such as polyethylene. Modern Linear accelerators are capable of producing increasingly higher energy beams. With increase in beam energy comes an increase in shielding needs and special considerations for neutron contamination.1
Another factor to consider in shielding is the type of barrier material used. The value tenth value thickness (TVL) is used to represent the amount of material needed to reduce exposure by 1/10th.1 The TVL for lead is less than steel, which both have a lower TVL than concrete. In some cases, different combinations of lead, steel, or concrete can be used to meet the architectural limitations of a structure. If there is ample room a thick concrete wall can be used for all treatment room barriers. However, if space is limited it may be necessary to use lead or steel which do not have to be as thick to provide the same level of protection.1
The designation of a treatment area is important when considering shielding. Areas surrounding a radiation treatment area are divided into two groups: controlled, and non-controlled.1 Controlled areas must be under supervision of a radiation safety officer and the maximum dose equivalent allowed for the area is .01 mSV/week. Non-controlled areas have a maximum allowance of .02 msv/week.2 Other shielding factors to consider are whether a wall is a primary barrier that protects from the primary radiation beam or a secondary barrier that protects from scatter or leakage radiation.1,2
All of the variables to consider in radiation shielding make it a complex topic. Time, distance, and shielding are the keys to radiation protection and these three factors combined are important in the subject of radiation safety. While the basics of time and distance may be conveyed in a simple and concise manner the topic of shielding is more involved and requires much consideration.
References
1.Khan FM, Gibbons JP. Radiation protection. The Physics of Radiation Therapy. Fifth Edition. Philadephia, PA: Lippincott Williams & Wilkins; 2014:348-360.
2.Casey Abing. Area Monitoring. Lecture presented: University of Wisconsin La Crosse; October 24, 2016