Health Physics Chapter 37 PDF

CHAPTER 37 HEALTH PHYSICS Health Physics Fluoroscopic Procedure  Concerned with providing occupational  It takes less than 5 minutes radiation protection & minimizing radiation dose...

CHAPTER 37 HEALTH PHYSICS Health Physics Fluoroscopic Procedure  Concerned with providing occupational  It takes less than 5 minutes radiation protection & minimizing radiation dose to the public Interventional Radiology Procedure  It takes more than 5 minutes Health Physicist  A radiation scientist who is concerned with Maximize Distance the research, teaching or operational aspects  Radiation dose is inversely related to the of radiation safety distance between the source & the patient  Assume a point source & apply the inverse RADIATION & HEALTH square law We Practice ALARA Inverse Square Law  Rationale: the linear nonthreshold radiation  It states that the intensity of radiation at a dose-relationship (LNT) for stochastic location is inversely proportional to the effects square of its distance from the source of o Examples: cancer, leukemia & radiation genetic effects  Formula: I1 (Old Exposure) d22 (New Distance Squared) Cardinal Principles of Radiation Protection =  Purpose: designed to minimize the radiation I2 (New Exposure) d12 (Old Distance Squared) exposure of patients & personnel  Time: keep the time of exposure to radiation If the distance from the source exceeds five as short as possible times the source diameter, it can be treated as  Distance: maintain as large a distance as a point source! possible between the source of radiation & the exposure person Square Law  Shielding: insert shielding material between  It states that one can compensate for a the radiation source & the exposed change in the source-to-object dstance by changing the mAs by the factor SID squared Minimize Time  It was used to calculate exposure in  The time of exposure should be kept to a radiographic technique minimum  Formula: o Radiography: to reduce motion blur I1 (Old Exposure) d12 (Old Distance Squared) o Fluoroscopy: to reduce patient & = 2 personnel exposure I2 (New Exposure) d2 (New Distance Squared)  Radiation dose is directly related to the X-ray Tube Target duration of exposure  A point source of radiation  Exposure = Exposure Rate x Exposure Time 122 Isoexposure Lines Fluoroscopic Footswitch  Lines that represent positions of equal  Sequencing on-off rather than continuous on radiation exposure in the fluoroscopy room Page during examination  Exposure Rate in Normal Position: 300 mR/hr or 3 mGya/hr 5-Minute Reset Timer  Two Steps Back: 5 mR/hr or μGya/hr  It reminds the radiologist that a considerable amount of fluoroscopic time has elapsed STEWART C. BUSHONG SUMMARIZED BY: MEYNARD Y. CASTRO  CHAPTER 37 HEALTH PHYSICS  Exit Dose: 0.1 mrad During fluoroscopy, the radiologic  Average Tissue Dose: 5 mrad technologist should remain as afar from the  Effective Dose: 1.35 mrad patient as practicable! o Lung = (5)(0.12) = 0.6 o Breast = (5)(0.05) = 0.25 Use Shielding o Esophagus = (5)(0.05) = 0.25  It greatly reduces the level of radiation o Thyroid = (5)(0.05) = 0.25 exposure  Composition: lead WEIGHTING FACTORS FOR VARIOUS  1 TLV = 3.3 HVL TISSUES  Protective Apron: 0.5 mm Pb Tissue Weighting o Equivalent to 2 HVLs Tissue Factor (Wt) o Reduce occupational exposure to Gonad 0.20 25% Active bone marrow 0.12 Colon 0.12 Half-Value Layer (HVL) Lung 0.12  The thickness of absorber necessary to Stomach 0.12 reduce radiation intensity to half its original Bladder 0.05 value Breast 0.05 Esophagus 0.05 Tenth-Value Layer (TVL) Liver 0.05  The thickness of absorber necessary to Thyroid 0.05 reduce radiation intensity to one-tenth its Bone surface 0.01 original value Skin 0.01 EFFECTIVE DOSE We assume the occupational effective dose to be 10% of the monitor dose! Radiation Risk Coefficient  Based on total body radiation exposure RADIOLOGIC TERRORISM Effective Dose Emergency Responder  The equivalent whole-body dose  Those individuals who must make the first  Formula: E = ∑DtWt decisions & take the first steps in the early stages of such an event Equivalent Whole-Body Dose  Radiologic Technologists: first emergency  The weighted average of the radiation dose responders to various organs & tissues  Tasks: o To prevent injury & death CT of the Abdomen & Pelvis o To attend to the medical needs of 123  Tissue Dose: 2000 mrad victims  Effective Dose: 740 mrem o Gonads = (2000)(0.2) = 400 Rescue & medical emergencies should be Page o Colon = (2000)(0.12) = 240 attended to before radiologic concerns are o Liver = (2000)(0.05) = 100 addressed! PA Chest Radiograph Radiologic Devices  Entrance Skin Dose: 10 mrad  Radiation Exposure Device (RED) STEWART C. BUSHONG SUMMARIZED BY: MEYNARD Y. CASTRO  CHAPTER 37 HEALTH PHYSICS  Radiologic Dispersal Device (RDD)  Detection Apparatus:  Improvised Nuclear Device (IND) o It should be readily available to the first responder Radiologic terrorism can be addressed safely o Capable of measuring radiation with an emergency responder’s equipment kit! exposure levels to 50 R/hr o It should emit ambiguous alarms at RED 10 mR/hr, 10 R/hr & 50 R/hr  A sealed source of radioactive material that  Storage: nuclear medicine laboratory directly exposed people  Decontamination is not required Radioactive contamination is rarely life o Rationale: it will not dispersed threatening! radioactive material RDD  A bomb that when exploded disperses radioactive contamination over a wide area  It is not usually life threatening  It may not be explosive, but rather, radioactive material  Forms: powder, mist, gas into a water supply or ventilation system IND  It contains nuclear material that can produce a nuclear explosion  A nuclear weapon Radiation Protection Guidance  With the use of radiation monitoring instruments  Inner Boundaries: established at an exposure rate of 10 R/hr  Outer Boundaries: established when exposure exceeds 10 mR/hr Being exposed to radiation does not make an individual radioactive! Radiation Detection & Measurement Equipment 124  Equipments: o Protective coveralls o Shoe covers Page o Protective respiratory devices o Contaminated-to-clean step-off pad STEWART C. BUSHONG SUMMARIZED BY: MEYNARD Y. CASTRO