Equipment Design for Radiation Protection PDF

Equipment Design for Radia4on Protec4on Part II  Design of Protec4ve Barriers A medical physicist must be consulted in designing proper radia4on shielding. Two basic types of barriers: Primary & Secondary barriers.  Primary radia4on is the most intense and therefore...

Equipment Design for Radia4on Protec4on Part II  Design of Protec4ve Barriers A medical physicist must be consulted in designing proper radia4on shielding. Two basic types of barriers: Primary & Secondary barriers.  Primary radia4on is the most intense and therefore the most diEcult to shield. Any wall to which the useful beam can be directed is called a primary barrier. 3 of the 4 walls in a Hxed x-ray lab are primary barriers as well as the Koor.  Lead bonded to sheet rock or wood paneling is the most oNen used as a primary barrier. Concrete or brick may be used instead, 4 inches of masonry is equal to 1/16 an inch of 1 umm or. lead. The primary barrier is perpendicular to the central ray.  Secondary barriers are designed to stop leakage and scaTer radia4on. The primary beam should never be pointed at a secondary barrier. The pa4ent is the source of most scaTer radia4on produced.  Leakage radia4on is emiTed from the tube housing in all direc4ons other than the primary beam. There is usually a lead glass window in the secondary barrier that is 1.5mm of Pb. The regulatory limit of leakage radia4on is 100mR/hr. at 1m distance. AmGy/hr & Im  InKuencing Factors Workload – measured in mA per min. or week (how much ac4vity is an x-ray room). Use factor – Walls are asigned a use factor of ¼ and the Koor is a 1. ( The amount of 4me the beam is directed at a wall or Koor.) The use factor for a secondary barrier is always a 1.  Occupancy Factor (T) Controlled Area- area occupied by radia4on workers: exposure rate is set at a limit of 100mR/week. 1mby Occupancy Factor (T) Uncontrolled Area – an area, such as a corridor, wai4ng room, or restroom where non-occupa4onal people are. 10mR/week is the limit. 1mGy/year  Radia4on Barriers 3 quali4es of the Primary Barrier: CR is perpendicular 1/16 of an inch of Pb or 1 6 mm. 7 feet tall  3 quali4es of the Secondary Barrier: CR is parallel 1/32 of an inch of PB or 0 8 mm. 7 feet tall  Types of Wearable Protec4ve Devices Lead aprons – minimum.25mmPb for standard x-ray Fluoro aprons are.5mmPb Lead glasses are.35mmPB Thyroid shields are.5mmPB Lead gloves are.25mmPB  Pa4ent Shielding Flat contact shield Shaped contact shields (best for pt. dose) Shadow shields – used for a procedure that is has a sterile Held.  SI units: close Equivalent Sieverts Effective · Dose , tissue Syt Grays = in Grays Absorbed dose Gya Grays in Air : = Coulmbs/Kg Primary beam : Becquerels Radioactive :  ESE Deceases When You Use: ↓ Entry Skin Exposure A 80kv@20mAs Proper Posi4oning 20kv & 20 mAs. Crig B C. Immobiliza4on her IR exposure Higher KV Lower mAs gher pt close High Filtra4on Collima4on Shielding