RadBio Chap 35 & 36

primary barrier

• located perpendicular to the undeflected line of travel of the x-ray beam

• most intense / hazardous

primary protective barrier

any wall to which the useful beam can be directed

thickness of primary protective barrier

• 1/16 inch thick Lead (Pb)

height of primary protective barrier

• 7 ft

• 2.1 m

secondary barriers

• are designed to protect against secondary radiation

  • scatter

  • leakage radiation

thickness of secondary protective barrier

• 1/32” lead (Pb)

• .8 mm

• should overlap the primary protective barrier by about 1/2” (1.3 cm)

radiation guidelines based upon

late effects of radiation

Internal Commission on Radiologic Protection (ICRP)

• provides recommendations on occupational & public dose limits to the NCRP

• make recommendations for EfD & EqD limits

• provider recommendations on occupational & public dose limits

  • not responsible for setting dose limits

  • provides information to NCRP regarding the dose limits

National Council on Radiation Protection & Measurements (NCRP)

• responsible for setting occupational, public, & prenatal dose limits based on the data provided by the ICRP

• make recommendations for EfD & EqD limits

• based on data provided by the ICRP

National Academy of Sciences (NAS) / National Committee on the Biological Effects of ionizing radiation (NRC-BEIR)

• reviews studies of the biological effects of ionizing radiation & risk assessment

• make recommendations for EfD & EqD limits

• provides information to ICRP

Food & Drug Administration (FDA)

regulates the design & manufacturing of electronic products including x-ray equipments

Environmental Protection Agency (EPA)

responsible for protecting the health of humans & for safe guarding the natural environment

Occupational Safety & Health Administration (OSHA)

• functions as a monitoring agency in places of employment

• regulates

  • occupational radiation exposure

  • training program

  • regulations/employees’ right to know

Nuclear regulatory commission (NRC)

• controls the possession, use & production of atomic energy

• requires each imaging facility to have an effective & detailed radiation safety program

• enforces radiation protection standards

• oversee & supervise the nuclear energy industry

radiation safety officer responsibilities

• development of radiation safety program

• assuring that all radiation guidelines are adhered to

• assuring that personnel understand & employ radiation safety measures

• maintain radiation-monitoring records for all personnel

• provide counseling for individuals who receive monitor readings in excess of allowable limits

least ideal to hold a patient for a static exposure

personnel

ideal to hold a patient for a static exposure

male friend / family

best option for a patient who will not hold still for a static exposure

immobilization device

three cardinal principles of radiation protection

• time

• distance

• shielding

ways to minimize time under fluoroscopy

• pulsed exposures

• 5 min reset timer

time related dose formula

exposure = exposure rate (exposure time)

decreasing your distance by 1/2

increases your radiation exposure by 4 times the initial intensity

doubling your distance

decreases your radiation exposure by ¼ of the initial intensity

point source of radiation

x-ray tube target

1 TVL =

3.3 HVL

1 HVL =

decreases intensity to 50%

2 HVL=

decreases intensity to 25%

3 HVL =

decreases intensity to 12.5%

last line of defense when time is minimized & distance is maximized

shielding

effective dose

• equivalent whole-body dose

• most accurate measure of dose for occupational, public & fetal exposure

• takes into account

  • type of radiation

  • type of tissue

  • total quantity

• DOES NOT INCLUDE SKIN & EXTREMITIES

type of radiation received

radiation weighting factor (Wr)

type of tissue irradiated

tissue weighting factor (Wt)

total quantity received

absorbed dose

effective dose unit of measurement

sievert (Sv)

Effective dose (EfD)

D x Wr x Wt

whole body effective dose calculations include

• gonds

• blood-forming organs

• lens of the eye

When managing a radiation victim with surface contamination, patients should:

• remove clothing

• shower to cleanse skin

• clothing should be placed in plastic containers

When managing a radiation victim with surface contamination, personnel should wear

• owns

• masks

• gloves

Do normal bade limits apply in emergency situations

NO

Radiation Safety Officer

• Who is responsible for assigning an individual to establish the emergency response equipment store

• ensuring adequate continuing training is provided to those who may be called upon to perform as emergency responders

secondary barrier

operator console booths

x-ray tube housing

factors considered when calculating barrier thickness

• distance

• occupancy

• control

• workload

• use factor

• kVp of operation

as the distance from the source to the barrier decreases

the barrier thickness must increase

secondary barrier use factor

1

use factor

percentage of time during which the X-ray beam is on & directed toward a particular barrier

x ray tube housing

• seconday barrier

  • protects us from leakage radiation

how many times must x-rays scatter before reaching behind barrier?

2 times

exposure control

fixed to the operator console

requirements of control panel

• audible signal

• indicate when the x-ray tube is one

• kVp, mA & s indicator

collimator functions

• residents off focus radiation

• decreases patient exposure

• confines beam

beam alignment

mechanism to ensure proper alignment of x-ray tube with IR

inherent filtation

• glass envelope

• insulating oil

• glass window

added filtration

made of sheets of aluminum

aluminum atomic number

13

image intensifier distance

short as possible

above 70 kVp

2.5 mm Al

50-70 kVp

1.5 mm Al

50 kVp

0.5 Al

foot pedal / positive pressure switch

• satisfies the requirement for the exposure control to be dead man type on the fluoro unit

• dead-man switch

controlled area

• areas occupied by radiology personnel & patients

• barrier must reduce exposure to less than 1 mSv/ week

bucky slot cover & protective curtain protects from

operator from scatter

cumulative timer

produces an audible signal to ensure the radiologist is aware of the relative beam on time during each procedure

geiger-muller counters characteristics

• used to determine the presense of radiation

• not for precise measurment

• most effective in detecting particulate radiation

• least effective in detecting x-ray/gamma radiation

scintillation detection device characteristics

• radiation stimulates scintillators to emit light → converted to an electrical signal

• used in nuc med & CT

ionization chamber instrument characteristics

• used to evaluate

  • leakage radiation

  • patient exposure

  • equipment performance

    • calibaration of x-ray equipment

radiation interactions in air produce

• ions (free e-) which produce an electrical charge

• read by an electrometer

personal monitoring devices register

• x-rays

• gamma rays

• beta rays

• neutrons

exposed border

should be visible at all heights above the tabletop

personnel monitoring provided to workers

who accumulate 1/10th or 10% of the allowed annual effective dose limits

reproducibility

should not exceed 5%

linearity

10% from one mA station to an adjacent mA station

exposure cord length

2m or 6 ft

Stationary fluoroscopy

38 cm (15”)

mobile fluoroscopy

30 cm (12”)

minimal source to end of collimator distance

30 cm

tube under the patient

• reduces

  • patient dose

  • scatter

primary protective barrier

2 mm Pb

fluoroscopy exposure control

• dead man type

• foot pedal / positive pressure switch

bucky slot cover

0.25 mm Pb

protective curtain

0.25 mm Pb

table top intensity fluoroscopy

should not exceed 21 mGya/ min / mA at 80 kVp

tabletop limit without high level control

should not exceed 100 mGya/min

tabletop limit with high-level control

should not exceed 200 mGya/min

leakage radaition

should not exceed no more than 1 mGya/hr @ 1m

advisory groups

• ensure public safety

  • NCRP

  • ICRP

  • NAS-BEIR

• make recommendations for EfD & EqD

regulatory agencies

• enforce the standards

  • NRC

  • FDA

  • EPA

  • OSHA

  • agreement states

radiation protection guidelines

• based on the late effects of radiation

• linear nonthreshold

Committee on biological effects of ionizing radiation (BEIR)

• review of avaliable biologic & biophysical data

• supports linear non threshold risk model

NAS-BEIR

non agreement states

• agreement between state & NRC

• NRC assumes responsibility for enforcing radiation protection regulations through its respective health departments

• inspects x-ray equipment

• ensures compliance with radiation safety regulations

radiation safety program

• NRC requirement of facilities providing imaging services

• provides guidance

doubling distance from radiation source decreases radiation exposure by

¼ the inital intensity

decreasing distance from the radiation source increases radiation exposure by

4 times the initial intensity

sheilding

last line of defense when time is minimized & distance is minimized

Radiation weighting factor

always 1

tissue weighting factor

takes into account that some tissues or organs are more succespitble to

factors that affect x-ray quality

• increasing

  • kVp = higher energy x-rays

  • filtration = higher average energy of the beam

negligible individual dose

0.1 mSv/year EfD

whole body effective dose calculations DO NOT include

• skin

• extremities

uncontrolled area

• areas occupied by anyone

• A protective barrier should ensure no one is exposed to more than 25 µSv in any one hour