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Sensitivity to Radiaiton&

Calculating pt dose& more “math” problems

Stat ch 8

Bush ch 40

Rev 2012 - week 7 - day 2

2Tissue and Cell Sensitivity to

Radiation

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Tissue Radiation Sensitivity

• Most Sensitive: • Reproductive organs• Blood-forming organs• Thyroid• Breast• Skin• Gastrointestinal

• Least sensitive:• Bone and teeth• 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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Organ or Tissue Weighting Factor (WT)

Gonads 0.20

Red bone marrow 0.12

Colon 0.12

Lung 0.12

Stomach 0.12

Bladder 0.05

Breast 0.05

Liver 0.05

Esophagus 0.05

Thyroid 0.05

Skin 0.01

Bone surface 0.01

Remainder†,‡ 0.05

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TABLE 3-3 Organ or Tissue Weighting Factors

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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

• “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??

11•LOOK AT CHART: mr/mas

PG 210 Stat PA chest 110 kvp (mR/mAs)72″=9.5

Lateral chest (mR/mAs)72″=9.5

CALCULATION

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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

• If a barrier separates an x-ray room from a hallway where the general public may occupy, then the shielding is designed to limit the amount of exposure in the hallway to?:

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More problems

• At 2 foot from a source the output intensity is 300 mR/hr and you were there for 20 minutes.

• What is the dose?

• What is total exposure received when you move 5 feet away and stay there for 40 minutes?

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• During fluoro, using 80kVp, the intensity at the table top per mA should not exceed ____ /ma/ minute?

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• Which of the following would produce the least patient dose?

• A. 85 kv 100 ma .12s

• B. 74 kv 100ma .12s

• C. 74 kv 100 ma .06s

• D. 74 kv 200 ma .06s

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• Using the Nomogram Chart – calculate

• the patient’s total skin dose for Port AP Chest @

• 40” SID (12” pt thickness), using 5mas

• 100 kVp, • 2.5mm filtration

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24 1. If during an Nephrostrogram exam using 80 kvp –

2. the Primary tube current output @1 ft was 2 R/mA/min

3. the fluoro tube operated at 0.5 ma.

4. What is the TUBE OUTPUT? _________/min

5. The RT received 150 mr/hr

6. of scatter @ 2 foot from the patient for 10 min

7. then moved 8 feet from the patient for another 10 min.

8. Answer for the following DOSE & Units

9. What was the total Fluoro time? _____________

10.WHAT WAS THE TOTAL EXPOSURE TO THE

11.PATIENT ________

12.TECHNOLOGIST _________________

• STAT: BOX 8-10 Information Needed to Develop the Request for Patient Radiation Dose Patient X-Ray Exam Record Form

• 1.The x-ray unit or units used for the study• 2.The projections taken• 3.The number of films associated with each projection• 4.Each projection's technical exposure factors (kVp,

mAs, image receptor size)• 5.The SID for each view• 6.The patient's AP or lateral dimensions at the site of

each projection• 7.For fluoroscopic irradiation, the approximate kVp, mA,

and especially the duration• 8.For spot films, the number taken, the kVp and mA

selected, and the approximate exposure time

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a. Spinal b. Muscle c. Skin d Thyroid

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Two of the most radiosensitive tissues with rapidly dividing cells in the body is ____ tissue.

Which one is most SENSITIVE

CELLS MOST SENSITIVE

• WHITE BLOOD CELLS – LYMPHOCYTES• RED BLOOD CELLS – ERYTHOROCYTES• BASAL CELLS OF THE SKIN• INTESTINAL CELLS• DEVELOPING NERVE CELLS OF EMBRYO• IMMATURE REPRODUCTIVE CELLS• EPITHELIAL CELLS THAT LINE BLOOD • LYMPHATIC VESSELLS (80% BODY)

CELLS THAT REPRODUCE THE MOST – SPEND THE MOST TIME IN THEIR REPRODUCTIVE STATE

LYMPHOCYTE PG.103

• SUBGROUP OF WBC

• ONLY LIVE FOR 24 HOURS

• ARE MANUFACTURED IN BONE MARROW

• MOST RADIOSENSITIVE BLOOD CELL

• 25 RADS CAN DEPRESS # OF CELLS

• LESS ABILITY TO FIGHT INFECTIONS

RHB – SYLLABUS PG 47MOST – LEAST SENSITIVE

• LYMPHOCYTES (WBC)• ETHROCYTES (RBC)• EPITHELIAL CELLS (SKIN)• ENDOTHELIAL CELLS (LINE BLOOD VESSELS• CONNECTIVE TISSUE CELLS• BONE CELLS• MUSCLE CELLS• NERVE CELLS• BRAIN CELLS

Radiosensitive Radioresistant

Breast tissue Heart tissue

Bone marrow cells Large arteries

Mucosa lining of small intestines

Large veins

Sebaceous (fat) glands of skin Mature blood cells

Immune response cells Neurons

All stem cell populations Muscle cells

Lymphocytes