Download Calculating pt dose

1
Sensitivity to Radiaiton
&
Calculating pt dose
& more “math” problems
Stat ch 8
Bush ch 40
Rev 2012 - week 7 - day 2
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Tissue and Cell Sensitivity to
Radiation
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Tissue Radiation Sensitivity
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Most Sensitive:
Reproductive organs
Blood-forming organs
Thyroid
Breast
Skin
Gastrointestinal
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Least sensitive:
Bone and teeth
Muscle
Nervous system
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Effects of Overdose to Humans
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Effects of Acute Radiation Exposures in Humans
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Why 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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TABLE 3-3 Organ or Tissue Weighting Factors
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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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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•LOOK AT CHART: mr/mas
• “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??
CALCULATION
PG 210 Stat
PA chest 110 kvp
(mR/mAs)72″=9.5
Lateral chest
(mR/mAs)72″=9.5
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•LOOK AT CHART: mr/mas
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PG 210 Stat
“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”
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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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• 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
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 _________________
24 1.
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• STAT: BOX 8-10 Information Needed to Develop the Request for
Patient Radiation Dose Patient X-Ray Exam Record Form
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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
26
Two of the most radiosensitive
tissues with rapidly dividing cells
in the body is ____ tissue
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Which one is most SENSITIVE
a Spinal
. c. Skin
b. Muscle
d Thyroid
CELLS MOST SENSITIVE
CELLS THAT REPRODUCE THE MOST – SPEND THE MOST
TIME IN THEIR REPRODUCTIVE STATE
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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)
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 47
MOST – LEAST SENSITIVE
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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