Radiation Protection RTMR 284 CHAPTER 21

Units Of Exposure Rad Rem The unit of absorbed dose.. Patient radiation dose is measured in units of rad Rem The unit of effective dose.. Dose to the whole body measured in units of rem Basis of dose limits

Units Of Exposure mRAD Gray - Gy Sievert –Sv The millirad is equal to one one-thousandth of a rad Gray - Gy The SI unit of absorbed dose equal to an energy deposition of Joule/kg = 10,000 ergs/gm (1 Gy = 100 rads). Sievert –Sv The SI unit of effective dose.

5 Ways Photons Interact with Matter Classical /Coherent scattering (occurs at < 10keV) Compton effect Photoelectric effect Pair production (occurs at 1.02 MeV) Photodisintegration (occurs at >10 MeV) Reference Chapter 7 for more details

Compton Effect Moderate-energy X-rays interact with outer- shell electrons This interaction scatters the X-ray (up to 180 degrees) reduces its energy (retains up to 2/3rds energy) ionizes the atom Compton effect occurs more above 80 kVp Compton effect occurring does not depend on the atomic # of the atom involved

Compton Effect Scattered X-rays provide no useful information on the image Compton-scattered X-rays produce fog Compton effect is the source of exposure to radiographers Radiation (large amounts) can be scattered from the patient, especially during fluoroscopy

Photoelectric Effect Diagnostic range X-rays undergo ionizing interactions with inner-shell electrons The X-ray is absorbed

Photoelectric Effect Photoelectric effect occurs more with: high atomic number material low energy X-rays Photoelectric effect occurs more below 80 kVp Name two materials that would result in more photoelectric effect occurring.

Atomic numbers or Z #’s Lead 82 Iodine contrast 56 Barium 56 Bone 14 Soft tissue/air 7 Fat 6

Comments Most of the photons (going through the patient) will interact & be absorbed by the tissue. Only ~5% of the incident photons will emerge from the patient to form the image ~50 % of the total number of photons reaching the image is from scattered radiation

4 Factors Affecting Scatter Radiation kVp (Kilovoltage peak) part thickness field size (area exposed, large coning) tissue density Scatter radiation is greatest with: high kVp large fields (open cone) - most important factor thick body parts dense tissue

Advantages of High kVp  skin entrance dose to the patient shorter exposures ( motion and blurring) increased radiographic latitude improved control of radiographic contrast tube not heated up as much due to better X-ray production efficiency at higher voltages The next slide is for your comprehension only – will not need to reproduce!

Factors Affecting Differential Absorption Higher atomic number (Z) PE absorption greater in absorbers with higher Z Compton scatter unaffected by Z number Increased kVp PE absorption decreases sharply Compton scatter remains proportionally greater Increased mass density PE absorption increases Compton scatter increases

ALARA As Low Reasonably Achievable What can we do as technologists to reduce radiation exposure???

Basic Principles of Radiation Redux Cardinal Principles: Time Distance Shielding How do we use these principles in our daily jobs as technologists?

Dose Limits Limiting Occupational exposure. Whole body: 5 rem / 50 mSv Quarter: 1.25 rem / 12.5 mSv Cumulative Effective Dose Limit E = N x 10 mSv, where N is the age in years. Study Table 21.3 in textbook.

Protective Apparel Type Pb Atten. Apron 0.50 mm 99.9% Gloves 0.25 mm 99% Thyroid 0.50 mm 99% Glasses 0.35 mm 99% Drape 0.25 mm 99% Holding Pt. Comments?

Patient Dose Reduction Techniques Repeats Shielding Flat contact Shadow Radiation Dose ESE – Skin entrance exp. Pediatrics Patients What exams have a high ESE???

Pregnant Radiographer & Patient Technologist: Have a choice to declare her pregnancy. Dose limit 0.5 mSv/mo. 5 mSv for pregnancy Baby Badge Wrap around apron Stay away from high dose procedures Patient: 10-day rule for patients. Ask EVERY TIME Keep dose low Talk to Radiologist if you feel the exam is unnecessary and the physician is insisting.