Biological response and radiation safety practices

Biological response and radiation safety practices X-ray interactions in the patient Radiation exposures Radiation measurement units Methods of detecting radiation Biological effects of radiation exposure Acute Radiation Syndrome Sub-syndromes-hemopoietic, GI, CNS Radiation Protection ALARA Biological response and radiation safety practices

Terminology NCRP R, roentgen, coulombs/kg rad rem Gray Sievert Curie, Becquerel Effective does Quality factor Threshold ALARA OSL Film badge TLD Pocket dosimeter Field survey instruments Geiger-Müller counter Cutie pie Somatic effect Genetic effect Acute Radiation Syndrome(ARS) Terminology

Radiation Exposure Units of measure International units British Units Exposure Measurements Methods of Measuring Units of measure International units British Units Unit conversions Film badge OSL TLD Pocket dosimeter Field Survey Instruments Radiation Exposure

What happens to our x-ray? Primary beam is the radiation that exits the x-ray tube. The Exit radiation is the radiation that builds our radiograph. The exit radiation is the x-ray photons that exit the patient.

Patient Interactions Classical Compton Photoelectric Pair Production Photodisintegration

Classical (Coherent) Scattering Patient Interactions Classical (Coherent) Scattering Excitation of the total complement of atomic electrons occurs as a result of interaction with the incident photon No ionization takes place Electrons in shells “vibrate” Small heat is released The photon is scattered in different directions Energies below 10kV WE can tell the difference between the heat and coherent because it is a photon incoming and exiting. The incoming photon comes in with a energy and changes direction leaving with the same amount of energy. Not useful in diagnostic radiology. Sometimes causes fog on the film. At a higher kVp a few of the classic coherent can add fog to the film.

Compton scattering COMPTON SCATTERING Outer shell electron in body Patient Interactions Compton scattering COMPTON SCATTERING Outer shell electron in body Interacts with x-ray photon from the tube 3. Moderate energy electron Outer shell rather than inner shell electron .

Photoelectric effect Patient Interactions photoelectron Incoming photon interacts with inner shell electron. The “knocked-out” electron is called a photoelectron. The energy of the incoming photon is absorbed.

Pair Production Patient Interactions Very high energy…not used in diagnostic radiology. It has enough energy to hit the nucleus and break off two parts of the nucleus: 1 positron and a negatron. This is bad because the nucleus contains DNA. But it is good for cancer, because it kills the cell. Incoming photon must possess a minimum of 1.02 mEv. (million electron volts). Interacts with nuclear electric field and causes it to dissapear. In its place we get two elecgtrons : one positron and one negatron. Electron eventaully will filla vacancy. Positron unites with a free e- and the mass of the both particles is converted to energy ina process called annihnilation radiation. We don’t use this in diagnostic radiology.

Patient Interactions Photodisintegration

X-rays interact with Patient’s body to cause changes in cells. Interaction in the body begin at the atomic level

Patient Interactions: Interactions of X-rays with matter No interaction: X-ray passes completely and get to image receptor Complete absorption: no x- rays get to image receptor Partial absorption with scatter-some x-rays get to image receptor but some get scattered No interaction; X-ray passes completely through tissue and into the image recording device. Complete absorption; X-ray energy is completely absorbed by the tissue. No imaging information results. Partial absorption with scatter; Scattering involves a partial transfer of energy to tissue, with the resulting scattered X-ray having less energy and a different trajectory. Scattered radiation tends to degrade image quality and is the primary source of radiation exposure to operator and staff.

X-ray photons can change cells Patient Interactions X-ray photons can change cells If the photon hits the nucleus it can kill the cell. The nucleus carries DNA.

To Keep Ourselves Safe: Radiation Exposures To Keep Ourselves Safe: Measure exposure Determine levels at which damage occurs

Measuring Exposure Units of Measure International Units British Units C/kg3 Gray Sieverts Becquerel British Units Roentgen Rad Rem Curie

Exposure: Measured in air

Absorbed Dose

Radiation Equivalent

RADS REMS rads Grays Patient absorbed dose rems Sieverts Employee (technologists) = In diagnostic radiology: 1 roentgen = 1 rad = 1 rem

Comparison of Units Exposure R C/kg 1R=2.58x10-4 C/kg Absorbed Dose rad Gray 1rad=.01Gray 1Gray=100rad Dose Equivalent rem Sievert 1rem=.01Sv 1Sv=100rem In diagnostic radiology: 1 roentgen = 1 rad = 1 rem

Unit Conversions: A normal chest x-ray exposes the patient to approximately 15mR. How many roentgens is that? A CT examination results in a patient dose of 4000 mrad. How many gray is that? Annual exposure dose for a technologist is 5 rems. What is that in Sieverts? mSv? You Receive ~620 millirem per year. According to stats from the US Nuclear Regulatory Commission average yearly exposure is roughly 620 millirem--half of which comes from natural sources (cosmic radiation, from the soil, radon, etc) and half comes from manmade sources. Note that geography can play a big part in that. In Colorado, for example, natural radiation exposure can be 1000 mrem per year due to higher altitude. What is your exposure in mSv? What is your exposure in mSv if you live in Colorado? A patient left a head of lettuce in the x-ray exam room. The lettuce received a dose of 10mrad. How many Gr is that?

Permissible Occupational Dose Annual dose : 5 Rem/year 50mSv/year 5000 mrem Cumulative Dose 1 rem x age or 10mSv x age

PUBLIC EXPOSURE NON MEDICAL EXPOSURE 10 % of Occupational exposure 0.5 rad or 500 mrad or 5mGray Under age 18 and Students 0.1 rem

Pregnancy & Embryo Mother occupational worker Baby 5 rem .5 rem/ year .05 rem/month

Methods of Measuring

Summary of Monitoring Devices

Exam 2 Next Week: ALARA- As Low As Reasonably Achievable