Radio I Lec 8 (7/6)

Annual occupational dose limits Total fetal

0.5 (5) 0.1 (1)

Fluoroscopic shilding

0.5 mm lead apron attenuates scatter by a factor of 20 For high work load &/or tube above table, thyroid collar & lead goggles Wrap-around adds protection Patient: gonads, eyes, thyroid Use shielded rooms when possible

Gondal shielding must b how thick?

0.5 mm lead equivalent

Gonadal shielding Three basic types: Contact/shaped contact Shadow -attached to collimator Mandatory equivalent?

0.5 mm lead equivalent Used only when does not interfere with required diagnostic info Must be protected if within field or within 5.0 cm of primary beam

Tenth value layer TVL

1 TVL = 3.3 HVL

Structural barriers Primary:

1/16" (1.6 mm) lead typical

Structural barriers Secondary:

1/32" (0.8 mm) lead typical Building materials such as concrete, gypsum, or lead acrylic also used Lead glass with 1.5 mm lead equivalent Often notrequired for mobile or low kVp X-ray machines

Childhood leukemia / malignancy Increased risk with in utero doses of about 2.0 rad Relative increased risk per rad?

= approx. 4x the risk if irradiation occurs in first trimester

Grids used for kVp's? &/or Body parts?

>70 >12.0 cm

Who should be monitored? (2)

Adults getting 1 year exposure in excess of 10% of effective dose limits. Pregant females getting deep dose equivalent of 1 millisievert (0.1 rem) over pregnancy.

ALARA principle avoid unnecessary exposure

As Low As Is Reasonably Achievable.

Operator safety Structural barriers Minimize scatter radiation Never stand in primary beam

Avoid holding patient Use lead gloves Have mother hold child Wear apron

Active bone marrow distribution adults

Axial skeleton has the most

Shielding

Barriers Aprons

Fetal mental retardation Rapid neuronal development of cerebral hemi.s greatest between 8th & 16th weeks Linear, non-threshold model

But -questionable risk below 1.0 rad Data from Hiroshima/Nagasaki studies Risk is approx. 0.4% per fetal rad After 15th week, risk is 0.2% per fetal rad with doses > 50 rads

Pregnant pts REASONABLY SUSPECTED FETAL RISKS:

Childhood cancer Small head size Malformation/ skeletal malformation Mental retardation Spontaneous abortion

grids lead strips

Control scatter

New max permissible dose

Cumulative/lifetime limit changed to 1.0 rem (10 mSv) x agein 1987 Adoption of Effective Dose Limits (abandoned MPD) in 1990 Monthly fetal doses established General organ standards set at 500 mSv(50 rem) occupational

Dose from Dx x ray What is the safest?

Dexa bone scan. hand foot very low

Protect pt Limit X-ray beam field size Minimize repeat studies

Do it right the 1st time Processing quality assurance Identify patients who are pregnant & possibly pregnant (confirm LMP) X-ray only if absolutely necessary Filtration

Optically stimulated luminescent dosimeter Most sensitive Plastic discs infused with aluminum oxide doped with carbon (Al2O3:C)

Encased in light tight container Worn just like film badges or TLDs Store energy when exposed to ionizing rad. Energy released as luminescence emitted (420 nm -violet) when OSLD illuminated to stimulated light (540 nm -green)

Effective dose (E) Most medical procedures result in a nonuniformdose distribution within the patient!

Equantifies the risk from partial body exposure to that from an equivalent/uniformwhole body dose

Personal monitors

Film Badge Thermoluminescentdosimeter (TLD) Optically stimulated luminescence dosimeter (OSLD)

Structural shielding Specification of barrier thickness derived from HVL/TVL of beam @ a room position

Generally determined for the highest energy level machine will employ Timer afixed inside shield -must not be able to make exposure outside of barrier Occupied areas/workload determination

Max permissible dose Assumes linear, non-threshold model Largest allowable rad. dose that is not expected to result in significant effects

In any given year, can exceed annual dose limits provided not over lifetime 5(N -18) < 18 y/o:Not employedin rad. occupation Max 0.1 rem of whole body radiation

Structural shielding Primary beam radiation

Is the actual beam directed at you?

Relative dose per study for fetal dose Highest? (adult / fetal)

Lumcosacral spine (AP) 250 / 80 mR Abdomen 220 / 70

Operator safety Ignorance is the greatest enemy! Know what you are doing & demand safety Personnel monitoring:

Monitor any person likely to receive, in one year, a dose in excess of 10% of their occupational dose limits [ODH 3701:1-38-14 B1(a)] Time, distance, and shielding

Film badge Pros and cons Provides permanent record

Monthly or quarterly Control badge for air kermaand/or background radiation Inexpensive Latent image fades with time -film should be developed within 1 -2 months Heat can affect film & give false readings

Annual occupational dose limits Lifetime

NCRP ICRP rems (mSv) 1.0 (10) x age N

Annual occupational dose limits Annual eye lens

NCRP ICRP rems (mSv) 15 (150)

Annual occupational dose limits Whole body

NCRP ICRP rems (mSv) 5 (50) 2 (20)

Annual occupational dose limits Skin, hands, feet

NCRP ICRP rems (mSv) 50 (500)

Fluoroscopy positioning

One step back from table can cut exposure rate by a factor of 4 Move image intensifier closer to patient Less patient exposure More scatter intercepted by tower Sharper images Lateral fluoroscopy: Stand on I.I. side!

Operator safety Understand what you are doing!

Personnel monitoring Distance Structural barriers Minimize scatter radiation Avoid primary beam

Pregnant worker May continue to work, but shouldwear extra badge at abdomen beneath apron Some workers chose to change badge every 2 weeks

Pregnant Should not exceed0.5 mSv (50 mrem) in any one month or5.0 mSv (0.5 rem) over entire pregnancy Remedial action> 0.3 mSv (30 mrem)

Pregnant worker Declarationof pregnancy must be in writing and is voluntary Employer not required to restrict the dose to embryo/fetus to 0.5 rem until written declaration

Pregnant worker Revocation at any time, in writing Monitor required if likely to exceed 10% of pregnant worker limit 0.5 rem/yr and/or 1% ALI

Scatter fields in fluroscopy (counter intuitive)

Primary little to none.

Structural shielding Secondary radiation:2 types

Scatter radiation-pt. major source Leakage radiation--emanates from the tube head in all directions (100 mR/hrat 1meter = max. limit)

Fluoroscoopic exposure TO PERSONNELAT TABLE SIDE, NO LEAD APRON 2 mGy/hr (200 mrad/hr) during fluoro. 30 mGy/hr (3000 mrad/hr) during boost (high dose rate) mode Rule of Thumb

Scatter to unshielded personnel 1 foot from patient is 1/100 of the patient's skin exposure 1/1000 at 1 meter

Childhood leukemia / malignancy Estimating patient does Data generally available from tables Can be misleading as patient doses can vary greatly from office to office 3 General indicators:

Skin dose (ESE) -most often reported Gonadal dose -the GSD Bone marrow dose -target organ for leukemia

Thermoluminescent dosimeter (TLD) Non-metallic crystalline solid lithium fluoride (LiF) -electrons excited to metastable state (radiation "stored")

Stability restored when heated, emitting light quantitatively proportional to X-ray energy absorbed High dynamic range: 5 mrad(mR) to 1000 rad for X-ray & gamma radiation

Effective dose (E) Quantity devised to account for the fact that exposures to people are nottypically spatially uniform Head, legs, arms unprotected,even with aprons

That dose which would have to be given to entire unprotected body to produce same health riskas the non-uniform dose received while wearing the apron

Protect the pt Minimize patient movement Keep exposure short

Use double screens, ideally rare-earth Electronic timers Use lead apron shields Exposure factors -maximize kVp while minimizing mAS

Film badge Cheap and simple Sensitivity: 10 mrem(mR) to 500 rem Plastic film holder with copper, lead, or aluminum filters

Uses film to measure radiation Filters help estimate general energy range of radiation Monitors X-, gamma & alpha particles Film darkening read with densitometer

Max permissible dose SPECIFIED FOR:

Whole-body radiation exposure Partial-body radiation exposure Organ exposure General population

Relative dose per study for fetal dose Lowest? (adult / fetal)

Wrist and foot. 5/0 mR Chest. 10/0 mR

Lead safety garments Aprons: 0.5 mm lead typical for 10beam 0.25 mm lead for 20beam radiation A 0.5 mm lead apron reduces exposure by?

at least a factor 10 Lead gloves -at least 0.25 mm Thyroid shield & eye goggles (fluoroscopy)

Optically stimulated luminescent dosimeter OSLs are the?

best most sensitive cost effective

Thyroid shields, leaded goggles... Recommended when monthly collar badge readings exceed 4 mSv (400 mrem) Badges worn outside shield on left collar or?

clipped onto left side of thyroid shield C-arm fluoroscopy-when X-ray tube is above the table Mobile shields for ancillary personnel who must be in room but are not performing patient-side work (badge?)

Time- fluoroscopy Use freeze frame (last image hold) whenever possible Use pulsed fluoroscopy (if?

designed to reduce dose) Use record mode only when permanent record is required Do not expose patient unless physician is viewing image

Structural barriers Primary is ____ to secondary (radiation)

double shielding thickness.

The effective dose is arrived at by taking the equivalent dose HT(weighted dose of an organ) and

factor in the sum of all weighted equivalent doses in all tissues and organs

Barrier thickness generally determined for

highest energy level employed by x ray unit

Least amount of exposure for tech?

image intensifier side

5X dose reduction on

intensifier side w lateral fluoroscopy

Optically stimulated luminescent dosimeter Most sensitive, measuring radiation as low as 1.0 mR Processed by exposure to?

light, not heat (TLD); no thermal quenching Isotropic response to radiation -no directional dependence Energy independence

Eye lens cataracts are what kind of effect?

long term deterministic.

Occupational dose monitoring Requried when there is any likelihood that an individual will receive?

more than 1/10 the recommended dose limit.

Radiation biological effects depend not only on type and energy or the radiation, but also

on type of tissue or organ that has been exposed Tissue weighting represents relative contribution of an organ or tissue

Timer/ button is fixed in or on?

shield