Transcript Rad T 110
Rad T 110 Radiation Monitoring and Protection Personnel Monitoring • Required when a worker may receive 10% or more of the annual MPD – Typically monitoring is done when 1% is expected • Placement – Collar level – Outside the apron if used • Second may be used for pregnancy • Extremity monitors also Types • Film badges – 10 mrem to 500 rem – Cheap • OSL; MC device today – Aluminum oxide which is read by a laser • Typically worn for 2 months – 1 mrem and sensitive to 5 keV to 40 MeV of energy Types cont. • TLD – Lithium floride – Reasonably sensitive • Cannot be re-read • Pocket ionization chambers – Good for immediate feedback • Not very reliable – Sensitive to mechanical energy Dosimetry Reports • Deep • Eye • Shallow doses Patient Protection • Effective Communication – Verbal messages – Concise instructions – Appropriate communication Immobilization • Voluntary motion – Lack of control – Immobilization devices work with this group • Involuntary motion – Fast exposure times with high mA helps – Possibly increasing kVp will help • 15% rule shorter exposure – Fast film/screen combinations Beam Limiting Devices • • • • Diaphragms Cones Collimators Limit the amount of tissue the beam exposes – Also, limit the amount of scatter produced • Our exposure Variable Collimator • 2 sets of lead shutters limit the divergence of the beam • Collimator and light field – +/- 2% of the SID • Positive beam limitation (PBL) – Automatic collimator, collimates to the field size put in the bucky tray Filtration • Total filtration – Inherent plus added filtration • Inherent – Glass envelope – Oil – Window of the tube housing – 0.5 mm Al • Added – Aluminum added to meet requirements Total Filtration • • • • 2.5 mm Al > 70 kVp 1.5 mm Al 50 – 70 kVp 0.5 mm Al < 50 kVp Mobiles/portables and Fluoro units are required to have at least 2.5 mm Al Long wavelength photons Short wavelength photons Filter Half Value Layer (HVL) • This is the amount of aluminum required to reduce the beam intensity to half its original value. • This is variable based on the selected kVp – As kVp is increased the penetrability of the beam increases – Therefore, the amount of Al necessary to halve the beam intensity will have to increase as well. Protective Shielding • Gonadal shields – Gonads need to be shielded when they are within 5cm of the beam – Unless shielding will obscure anatomy – Required to have at least 0.5 mm Pb Types of Gonadal Shields • • • • Flat contact Shadow Shaped contact Clear lead Specific area shielding • Breast during scoliosis screening – Clear lead filter – PA instead of AP Compensating filters • Trough or bilateral wedge – For chest images • Wedge filter • Specialized metal filters – Copper Technical Factors • Technique charts • High kVp low mAs techniques – This is within a specific body part or region Film Processing and QC • The processor has to work correctly. If not, films will be poor and repeats necessary. • QC insures that the processor is maintained to a standard level of acceptance Film/Screen • Rare earth screens are generally faster – This occurs due to their higher atomic number which results in a higher absorption of photons. Consequently, more light is produced per photon meaning less photons have to be used for a good film. Grids • Prevent scattered radiation from reaching the film. • They actually increase pt dose. • However, film quality is dramatically improved. Repeat Analysis • Systematic review of repeated films to determine trends that can be eliminated thru education, procedural changes, or equipment maintenance. Unnecessary Procedures • Make sure films are completed and recorded. • Listen to pts about possible previous exams. • When in doubt ask. SID • Must be a minimum of 12 inches • The longer the SID the lower the pt dose Digital Imaging • CR and DR are the two methods currently used for digital diagnostic imaging • Images are displayed on a computer for viewing – Analogous to digital pictures at home • Image quality can be manipulated post acquisition – Possible reduction in repeats Fluoroscopy Procedures • High pt dose – Potentially high tech exposure • Exams provide dynamic info • ‘real time’ feedback for positioning of devices Dose recording to patients • ESE – Entrance skin dose • GSD – Genetically significant dose • Bone marrow dose Pregnant pts • Should not be radiographed – If necessary, informed consent should be obtained • Pts needed to be asked about potential pregnancy before the exam begins Pediatrics • More radio-sensitive than adults • More likely to move • Need to get instructions they understand not fear • Gonadal shielding collimation Protection of Personnel • MPD • ALARA Dose Reduction Methods • • • • • No repeats Patient is the source of scatter Filtration Protective apparel Technical factors Pregnant personnel • • • • Lower MPD Protective apparel Additional monitoring Work schedule alteration Basic Principles of Protection • Time • Distance • Shielding Structural Shielding • Primary – 7 feet high – 1/16 in Pb • Secondary – 1/32 in Pb • Operator booth – Photons should scatter at least twice before entering the booth area – Secondary barrier