8 - Radiation Safety Flashcards
Radiobiology
- The effects of ionizing radiation on biologic tissue
- Not known whether there are effects from diagnostic x-rays
- Always use lowest permissible dose
What are the two human responses to ionizing radiation?
- Stochastic effects
- Deterministic (non-stochastic) effects
Stochastic effects
Stochastic effects: responses where probability of occurrence increases with dose; ie, the higher the dose, the greater the chance of effects
Deterministic (nonstochastic) effects
Deterministic (nonstochastic) effects: severity of response increases with dose; i.e., the higher the dose, the more severe the response
Describe when we see stochastic effects
** KNOW FOR EXAM **
- Do not have a threshold dose and are observed for months or years ***
- Result from low radiation doses over a long time ***
- Include leukemia, bone, breast and lung CA
- Include radiodermatitis and cataracts
- Infant exposure produces 4x the cancer risk of adults
Describe when we see deterministic (non-stochastic) effects
** KNOW FOR EXAM **
- Have threshold dose which needs to be exceeded before response is seen and severity of response proportional to dose ***
- Occur early within minutes or days ***
- Radiation sickness causes death to hematologic, GI, and nervous systems ***
- Skin desquamates, ovaries and testes atrophy and become sterile
- Prenatal and neonatal death, congenital malformation, childhood malignancy, diminished growth
Matching REVIEW
** KNOW FOR EXAM **
1 - Cataracts…
2 - Radiation sickness…
3 - Occurs in hours to days…
4 - Occurs in years…
1 - Cataracts… Stochastic effects
2 - Radiation sickness… Non-stochastic effects
3 - Occurs in hours to days… Non-stochastic effects
4 - Occurs in years… Stochastic effects
Effects of ionizing radiation on tissues
Law of Bergonie and Tribondeau
- Sensitivity of tissues depends upon proliferative capacity (rapidly dividing cells more sensitive than slowly dividing cells) and differentiation (fully differentiated cells less sensitive
- Most sensitive: bone marrow>lymphocytes>GI
- Most resistant: CNS
4 physical factors affecting radiosensitivity
- Linear energy transfer (LET)
- Relative biologic effectiveness
- Protraction
- Fractionation
Linear energy transfer (LET)
Measure of amount of energy transferred along path of radiation
- Low: x-rays
- Medium: photons
- High: alpha particles (cause direct tissue damage)
Relative biologic effectiveness
Effectiveness of one form of radiation compared to another
Protraction
Radiation dose to neoplasm is delivered continuously, but at a lower dose rate
CONTINUOUS LOW DOSE
Fractionation
Same radiation dose rate to neoplasm is delivered in equal fractions, each separated by period of time
SEPARATE BOLUS DOSES
Biologic factors affecting radiosensitivity
- Tissues more sensitive when irradiated in the oxygenated state
- Utero and old age most sensitive
- Males more sensitive than females
- Cell is capable of recovery if it is not killed before next division
- Molecules with sulfhydryl group are radioprotective
- Vitamin K, methotrexate, actinomycin D are radiosensitizers
Matching REVIEW
** KNOW FOR EXAM **
More or less sensitive to radiation?
- Oxygenated tissues
- Molecules with sulfydryl group
- Adolescents
- Seniors
- CNS
- Bone marrow
More or less sensitive to radiation?
- Oxygenated tissues (MORE)
- Molecules with sulfydryl group (LESS)
- Adolescents (LESS)
- Seniors (MORE)
- CNS (LESS)
- Bone marrow (MORE)
Types of radiation dose-response relationships
- Linear nonthreshold
- Linear threshold
- Nonlinear nonthreshold
- Linear nonthreshold
Linear dose-response
Linear: response directly proportional to dose
Nonlinear dose-response
Nonlinear: response not directly proportional
Threshold dose-response
Threshold: no response produced at a dose below the theshold dose
Nonthreshold dose-response
Nonthreshold: any size dose is expected to produce a response
Irradiation of macrocolecules
- High doses of radiation kill cells immediately (you see sloughing off and dying skin right away)
- Low doses of radiation causes DNA damage (this results in defects over time)
Direct effects of radiation
- Radiation interacts directly with a molecule like DNA
- Accounts for small fraction of damage at low LET, but most of damage at high LET
Indirect effects of radiation
- Caused by free radicals formed from ionizing radiation interacting with body and associated with radiolysis of water
- Free radicals migrate from the initial site of ionization of DNA, transfers its excess energy and disrupts bonds
- Accounts for most damage at low LET
Matching REVIEW
** KNOW THIS **
1 - Response directly proportional to dose and any dose produces effects…
2 - Response not dependent upon dose, but no response will be seen if threshold dose not exceeded…
3 - Direct radiation effects…
4 - Non-direct radiation effects…
1 - Response directly proportional to dose and any dose produces effects… Linear nonthreshold
2 - Response not dependent upon dose, but no response will be seen if threshold dose not exceeded… Nonlinear threshold
3 - Direct radiation effects… Direct DNA damage
4 - Non-direct radiation effects… Free radical formation
Basics of ionizing radiation
X-rays are ionizing radiation-removes an electron from an atom-it is also non-particulate and uncharged radiation
How do you measure ionizing radiation
you had this yesterday, just a review
- Roentgen (R) or Air Kerma: quantity of exposure
- Rad or Gray (Gy): quantity of absorbed dose
- Rem (r) (“roentgen-equivalent-man”) or Sievert (Sv): quantity of effective dose equivalent received by radiation workers
- Curie or Becquerel: quantity of radioactivity
KNOW THE NUMBERS
1 Gy = 100 rad **** 1 rad = 1 mGy 1 rem = .01 Sv **** 1 rem = 10 mSv 1 rad = 1 rem 1 Gy = 1 Sv
Just know the starred ones
What is the annual whole body dose of ionizing radiation from NATURAL sources?
300 mrem (3 mSv)
Internal radioactive potassium-40, cosmic rays, radon
What is the annual whole body dose of ionizing radiation from MAN-MADE sources?
630 mrem (6.3 mSv)
Diagnostic x-rays, smoke detectors
What is the rule of thumb for safe cumulative annual dose for an adult?
1/10 of age
For 40 year old, dose should not exceed 4 rem or 4000 mrem
What is the ALARA principle?
“as low as reasonably achievable”
Reduction and safety with radiation
What does ALARA include?
- Protective barriers
- Patient radiation exposure
- Radiation-protective clothing
- Dose limits
- Occupational radiation exposure
- Quality control
Protective barriers
Protective barriers: absorb x-rays such as concrete and lead
- Primary: protect from primary (useful) x-ray beam
- Secondary: protect from scattered and leakage radiation
Patient radiation exposure
- Only perform clinically justifiable exams
- Avoid repeat exams
- Technique chart should be attached to the control panel that includes the mA, kVp, and time of exposure for each positioning technique at the SID recommended by the unit’s manufacturer
Most machines will account for width (toes thinner than midfoot), but if they don’t, how do you compensate for this?
Caliper
- Caliper measures thickness of body part and combined with technique chart standardizes technical factors
Radiation protective clothing
- Lead aprons: normal thickness is 0.5 mm
- Lead gloves: 0.25 to 0.5 mm thickness
- Gonad shields: can be used on children instead of lead apron
Radiation protection during pregnancy
For pregnancy, use a high kVp technique and precise collimation of beam
Fetal dose risks
- Foot x-ray delivers less than 1 rad (1 mGy)
- A spontaneous abortion or birth defects would not occur until more than 10 rad (10 mGy)
- At 2 weeks of gestation, there would either be a spontaneous abortion or NO effect (no birth defects)
- At 2-8 weeks of gestation, there would be congenital abnormalities of the skeleton and nerves
- In the third trimester, leukemia could occur in childhood
Dose limits
KNOW FOR EXAM
- Prescribed for various organs, the whole body and various working conditions
- DL: the amount of radiation that if received annually runs the risk of death to 1:10,000 ***
- Formula for cumulative annual whole body occupational exposure is age (in years) x 1 rem
- Entrance dose of foot x-ray is
What are the limits for occupational radiation exposure
** KNOW FOR EXAM **
- Annual effective dose: 50 mSv (5 rem)
- Cumulative annual effective dose: 10 mSv (1 rem) x age
- Equivalent annual dose for skin, hands, feet: 500 mSv (50 rem)
- Equivalent annual dose for lens of eye: 150 mSv (15 rem)
- Pregnant worker: 5 mSv (.5 rem) for the 9 months of pregnancy
- Limits for children less than 18: 1 mSv (100 mrem) for annual exposure
- Limits for adult public: 1/10 that of radiation workers ***
Know all of these ***
Matching REVIEW
**KNOW FOR EXAM **
1 - Equivalent annual dose for feet
2 - Equivalent annual dose for lens of eye
3 - Annual whole body dose from natural sources
4 - Annual whole body dose from man-made sources
5 - Cumulative annual effective dose for 50 y/o radiation worker
6 - Cumulative annual effective dose for 50 y/o adult
7 - Annual effective dose
1 - Equivalent annual dose for feet (500 mSv)
2 - Equivalent annual dose for lens of eye (150 mSv)
3 - Annual whole body dose from natural sources (3 mSv)
4 - Annual whole body dose from man-made sources (6.3 mSv)
5 - Cumulative annual effective dose for 50 y/o radiation worker (50 mSv)
6 - Cumulative annual effective dose for 50 y/o adult (5 mSv)
7 - Annual effective dose
Describe radiation exposure during fluoroscopy
- Radiation exposure during fluoroscopy is directly proportional to the length of time the unit is activated by the switch
- Fluoroscopy machines are equipped with a timer and an alarm that sounds at the end of 5 minutes
- A typical exposure rate at the X-ray beam entrance into the patient (ESE, or Entrance Skin Exposure) is 2 R/min
- Limit of the ESE to 10R/min
Describe radiation dose received by operator
- The majority of the radiation dose received by the operator (provided the primary beam is avoided) is due to scattered radiation from the patient
- An operator positioned 3 feet from the X-ray beam entrance area will receive 0.1% of the patient’s ESE ***
Describe the dose accumulated by hands and eyes
- Doses accumulated to hands and eyes from frequently using the fluoroscope with the tube above the patient can be extremely high
- Only routine application of proper radiation management techniques will be effective at avoiding such high doses
What is Last-Image-Hold
- Use of Last-Image-Hold features, when available, allows static images to be viewed without continuously exposing patient and operator to radiation
- Standing one step further away from the patient can cut the physician’s exposure rate by a factor of 4 ***
What does the magnification mode do to the amount of radiation?
Magnification modes should be employed only when the increased resolution of fine detail is necessary due to the increased amount of radiation exposure during magnification procedures***
Collimating the primary beam
Collimating the primary beam to view only tissue regions of interest reduces unnecessary tissue exposure and improves the patient’s overall benefit-to-risk ratio
Steeply angled oblique images
Steeply angled oblique images (e.g., LAO 50 with 30 cranial tilt) are typically associated with increased radiation exposure
Surgeon standing on image receptor side of the table
dose rates can be reduced by a factor of 5 when the physician stands on the image receptor side of the table (versus X-ray tube side) during a lateral projection
Effectiveness of shields
Shields are most effective when placed as near to the radiation scatter source as possible (i.e., close to patient).
Who is required to wear a lead apron?
Whenever fluoroscopes are operated the operator and all staff within the room (or within 2 meters if using a mobile C-arm) are required to wear lead aprons.
Matching REVIEW
** KNOW FOR EXAM **
To limit radiation exposure when using C-arm…
A. limit use of the floor pedal
B. do not use the last-image-hold technique
C. do not use collimation
D. stand on the image receptor side of the C-arm
E. use magnification whenever possible
F. stand as close to the C-arm as possible
A. limit use of the floor pedal (yes)
B. do not use the last-image-hold technique (no)
C. do not use collimation (no)
D. stand on the image receptor side of the C-arm (yes)
E. use magnification whenever possible (no)
F. stand as close to the C-arm as possible (no)
Occupational radiation exposure
- Less time exposed to radiation, the lower the dose
- Greater distance from the radiation source, the lower the dose
- Maximize protective shielding
Film badge
A film badge (a whole body thermoluminscent dosimeter) estimates amount of individual exposure and worn on the torso between the neck and pelvic areas
Processed every month
Monitors workers who are expected to receive an annual dose > 10% of the occupational exposure limit
Holding the image receptor
Worker should never hold the image receptor
Quality control
Annual check of kVp calibration, mA linearity, exposure timer accuracy, collimation alignment, effective focal spot size, exposure reproducibility, and filtration
Give a review from yesterday regarding manual film processing…
Make sure you know this from yesterday’s lecture
Wetting
- Swelling of emulsion to permit subsequent chemical penetration
Development
- Production of manifest image from the latent image
- Changes silver ions of the exposed silver halide crystals into metallic silver and to concentrate this silver in the region of the sensitivity spectrum
- Prior to contact with the fixer, while in the developer, if the image is exposed to light it will be obliterated and look uniformly black
Stop bath
- Terminate development and remove excess chemical from emulsion
Fixing
- Removal of remaining silver halide from emulsion and hardening of gelatin
Washing
- Removal of excess chemicals
Drying
- Removal of water and preparation of radiograph for viewing
Radiopaque labeling tape
Semisoft strip of lead or tungsten mixture onto which is typed the pertinent patient information and is placed onto cassette before exposure
Right and left identification marker
Capital letters R and L are used to identify right and left extremities
What to know for exam
LISTEN AGAIN
- Know dose limits
- Definitions: annual effective dose, effective dose (and other terms like that)
- Know dose equivalents
- Stochastic vs nonstochastic
- Safety steps for flouroscopy (re-iterated from yesterday’s recommendations)
