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RadiationProtection
Chapter 39
| Question | Answer |
|---|---|
| Physicians rely on imaging more because: | - x-ray exams diagnostic accuracy and efficacy has improved-more difficult procedures are being completed in x-ray |
| Two important variables in the estimation of patient dose: | -Efficiency of x-ray production-Image receptor speed |
| Four ways to estimate patient dose: | Entrance Skin Exposure (ESE)Skin DoseMean Marrow DoseGonadal Dose |
| Entrance Skin Exposure (ESE) | -Most often referred to as patient dose-Looking at epidermal layer of skin-Easy and accurate to measure-Calculated at min. SOD-Usually meausred with TLD |
| Nomogram | used by physicist to measure ESE in absence of a patient |
| PA Chest ESE | 10 mrad |
| Extremity ESE | 10 mrad |
| Lateral skull ESE | 80 mrad |
| cervical spine ESE | 110 mrad |
| thoracic spine ESE | 180 mrad |
| abdomen ESE | 220 mrad |
| Fluoro: cassette-loaded spot films ESE | 200 mR per view |
| Fluoro: photo spots ESE | 100 mR per view |
| Fluoro: digital fluoro ESE | 200 mR per frame |
| Cineradiography ESE | 1000 mR/s at 15 frams/s |
| Mean Marrow Dose | -contains large number of stem or precursor cells and blood cells that could be depleted-only estimated (can't be done accurately)-important because bone marrow is the target organ believed responsible for radiation-induced leukemia |
| Average fluoroscopic examination ESE | 4 R/min |
| Gonadal dose importance: | because of possible genetic responses to medical x-ray exposure |
| US mean marrow dose from diagnostic x-ray examinations averaged over the entire population is: | approximately 100 mrad/yr |
| Genetically significant Dose (GSD): | the gonadal dose that, if received by every member of the population, would produce the total genetic effect on the population as the sum of the individual doses actually received |
| US GSD: | 20 mrad/yr |
| Glandular Dose (Dg): | approx. 15% of the ESE |
| Glandular Dose should not exceed: | 100 mrad/view with contact mommography200 mrad/view with magnification without grid300 mrad/view with a grid |
| 2 concerns related to patient dose in CT: | skin dose and dose distribution during the scanning procedures |
| Dose increase in CT is contributed to: | -some overlap of the margins of the x-ray beam occurs when each single section is made-some radiation scatter from the slice being made into the adjacent slice |
| Scan pitch ratio: | -the relationship between the movements of the patient table and the x-ray beam collimation-1:1 pitch ratio complarable with conventioanal CT-Higher pitch ratios = lower patient dose |
| Signal-to-noise ratio affected by: | -too few photons (mAs) used-the slection of pixel size-the selection of slice thickness |
| ESE for CT scan: | approx. 5000 mrad per scan |
| potential response to radiation exposure it dependent on: | Time (second-tenth week)Dose (no exact dose info known) |
| Major organogenesis: | Second - Tenth week of pregnancymain developmental period of organ systems |
| If pregnant femal must be examined, use: | tight collimationhigh kVp techniquesshielding |
| Factors affecting unnecessary dose: | unnecessary examsrepeat examsradiographic techniqueintensifying screenspatient positioning and shielding |
| unnecessary exams: | -routine examss when there is no precise medical indication-mass screening for TB-hospital admissions-pre-employment physicals-periodic health exams |
| types of specific area shielding: | contact shieldsshadow shieldsbreast shieldsthyroid shields |
| Ways to reduce patient dose: | communication, positioning, projection, immobilization, technical factors, collimation, shielding, compression, grids (increase), screens, processing |
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