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Sensitivity to Radiaiton&

Calculating pt doseStat ch 8

Bush ch 40

2Tissue and Cell Sensitivity to

Radiation

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Tissue Radiation Sensitivity

• Most Sensitive:

• Reproductive organs• Blood-forming organs• Skin • Bone and teeth

• Least sensitive:

• Muscle• Nervous system

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Effects of Overdose to Humans

5Effects of Acute Radiation Exposures in Humans

6Why cancer risks at low doses

are uncertain• It has been difficult to estimate cancer induction

risks, because most of the radiation exposures that humans receive are very close to background levels.

• At low dose levels of millirems to tens of rems, the risk of radiation-induced cancers is so low,

• that if the risk exists, it is not readily distinguishable from normal levels of cancer occurrence.

• In addition, leukemia or solid tumors induced by radiation are indistinguishable from those that result from other causes. 

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Relative Risk of a 1 in a million chance of death from activities common to our society:• ·Smoking 1.4 cigarettes in a lifetime (lung

cancer) • Eating 40 tablespoons of peanut butter

(aflatoxin) • Spending two days in New York City (air

pollution) • Driving 40 miles in a car (accident) • Flying 2500 miles in a jet (accident) • Canoeing for 6 minutes (drowning) • Receiving a dose of 10 mrem of radiation

(cancer)

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PATIENT DOSE

• RAD• MR/MAS PER EXPOSURE - At each kVp level

– there is a determined output for each radiographic room

• EX 70 kvp = 2.5 mr/mas• ABD done 70 kVp, 20 mas • 2.5 x 20 = 50 mR for that one exposure.• LOOK AT formula: mr/mas Ch 8 Stat • CH 40 BUSHONG

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• “AVE” CHEST EXPOSURE - 2 IMAGES

• (Ave – Pt meas 23cm pa 40cm lat)• PA 110 KVP 5 MAS 16:1 GRID 400RS 72”• LAT 110 KVP 20 MAS 16:1 GRID 400 RS 72”

• WHAT IS THE PATIENT’S DOSE??

•LOOK AT CHART: mr/mas PG 210 Stat

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• “AVE” CHEST EXPOSURE - 2 IMAGES

• WHAT IS THE PATIENT’S DOSE??

• OUTPUT OF TUBE NEEDED:

• PA Chest = mr/mas = 9.5

• LAT 110 KVP 20 MAS 16:1 GRID 400 RS 72”

•LOOK AT CHART: mr/mas PG 210 Stat

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• Which of the following technical factors will create the highest skin entrance dose to the patient?

• A. 80 kvp 300 ma .5s no filter B. 80 kvp 300ma 1/10s no filter

• C. 80 kvp 1000ma 1/20s 2.5mm al eq. filter • D. 80 kvp 800ma 1/60 sec .05mm al eq filter

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• The exposure rate to a tech at 4 feet from the source is 240 m R/hr. What distance would be necessary to reduced the rate below 60 mR/hr?

• A. 1 foot

• B. 6 feet

• C. 2 feet

• D. 9 feet

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• If the exposure at 2 inches = 9 R/min, what is the exposure at 6 inches from the source?

• A. 1 R B. 5 R C. 3 R

• D. 81 R E. 60R

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• If 85 kvp, 400ma 0.12s = 150mR - what is the mr/mas?

• A. 0.32

• B. 3.1

• C. 33.1

• D. 17.6

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• Primary radiation barriers must be at LEAST how high (in feet)?

• A. 5

• B. 6

• C. 7

• D. 8

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