1
Sensitivity to Radiaiton
&
Calculating pt dose
Stat ch 8
Bush ch 40
2
Tissue and Cell Sensitivity to
Radiation
3
Tissue Radiation Sensitivity
• Most Sensitive:
• Least sensitive:
•
•
•
•
• Muscle
• Nervous system
Reproductive organs
Blood-forming organs
Skin
Bone and teeth
4
Effects of Overdose to Humans
5
Effects of Acute Radiation Exposures in Humans
6
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.
7
8
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)
9
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
10
•LOOK AT CHART: mr/mas
PG 210 Stat
• “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
“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”
12
• 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
13
• 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
14
• 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
15
• If 85 kvp, 400ma 0.12s = 150mR - what
is the mr/mas?
• A. 0.32
• B. 3.1
• C. 33.1
• D. 17.6
16
• Primary radiation barriers must be at
LEAST how high (in feet)?
• A. 5
• B. 6
• C. 7
• D. 8
17