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Calculating pt dose Using Nomigrams Sensitivity to Radiation & more “math/dose ” problems. Bush Ch 36 & 31,32 & Stat Ch 8 Rev 2013 - week 7 - day 1 & 2. This family of curves is a nomogram for estimating output x-ray intensity from a single-phase radiographic unit.

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calculating pt dose using nomigrams sensitivity to radiation more math dose problems

Calculating pt doseUsing NomigramsSensitivity to Radiation& more “math/dose ” problems

Bush Ch 36 & 31,32

& Stat Ch 8

Rev 2013 - week 7 - day 1 & 2

slide2
This family of curves is a nomogramfor estimating output x-ray intensity from a single-phase radiographic unit

estimate the ESE from a lateral skull film taken at 66 kVp, 150 mAs, with a radiographic unit having 2.5 mm Al total filtration.

slide3

Estimate the intersection between a vertical line rising from 2.5 mm Al and a horizontal line through 66 kVp. Extend the horizontal line to the y-axis and read 3.8 mR/mAs

3.8 mR/mAs × 150 = 570 mR

slide5

A better approach requires that a medical physicist construct a nomogram such as that shown in Figure 40-4 for each radiographic unit. A straight edge between any kVp and mAs value will cross the ESE scale at the correct mR value.

  • Question: what is the ESE when a radiographic exposure is made at 66 kVp, 150 mAs?
  • Answer: The line is drawn as shown and crosses the ESE scale at 1000 mR.
slide7

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

slide8

LOOK AT CHART: mr/mas #13

  • PG 210 Stat 600 Bushong
  • “AVE” CHEST EXPOSURE - 2 IMAGES
  • WHAT IS THE PATIENT’S DOSE??
  • OUTPUT OF TUBE NEEDED:
  • PA Chest @ 110 = mr/mas = 5.5
  • PA 110 KVP 5 MAS 16:1 GRID 400RS 72”
  • LAT 110 KVP 20 MAS 16:1 GRID 400 RS 72”

How do you calculate dose for exam?

slide9

LOOK AT CHART: mr/mas

  • “AVE” CHEST EXPOSURE - 2 IMAGES
  • WHAT IS THE PATIENT’S DOSE??
  • OUTPUT OF TUBE NEEDED:
  • PA 5.5 x 5mas = 27.5 mRad
  • Lat 5.5 x 20 = 110 mRad
  • This does not take in account SSD for ESE
slide10

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
find the mr mas
Find the mr/mas
  • 100 kvp
  • 400ma 0.10s = 150mR –
  • what is the mr/mas?
calculate patient dose
Calculate PATIENT DOSE
  • USING A NOMOGRAM CHART – FIND mR/mAs
  • MR/MAS : At each kVp level – there is a determined output for each radiographic room
  • EX 80 kvp = ? Mr/mas (Find on Nomogram)
  • ABD done 80 kVp, 10 mas 40 “ SID
  • Patient Measures – 14 cm
  • Look at NOMIGRAM
    • to find mr/mas output for 80 kvp
  • Then determine what patient ESE is at SSD
slide14
“AVE” L.SP EXPOSURE - 5 IMAGES
  • (Ave – Ptmeas 23cm PA 40cm Lat )
  • PA 70 KVP 40 MAS 16:1 GRID 400RS 40”
  • LAT 80 KVP 80 MAS 16:1 GRID 400 RS 40”
  • WHAT IS THE PATIENT’S DOSE? ESE
  • How can you find out the mr/mas for this tube
  • Need mr/mas output for 75& 85 kvp 2.5mmAL
  • Use Nomogram to develop mr/mas for ESE
slide16
“AVE” CHEST EXPOSURE - 2 IMAGES
  • (Ave – Ptmeas 15 cm PA 30cm Lat )
  • PA 90 KVP 4 MAS 72”
  • LAT 105 KVP 8 MAS 72”
  • WHAT IS THE PATIENT’S DOSE? ESE
  • Find mR/mAs on nomogram & calcate dose
slide18

BUSHONG

TABLE 37-1 Representative Radiation Quantities From Various Diagnostic X-ray Procedures

Page 566 10TH ed

tissue radiation sensitivity
Most Sensitive:

Reproductive organs

Blood-forming organs

Thyroid

Breast

Skin

Gastrointestinal

Least sensitive:

Bone and teeth

Muscle

Nervous system

Tissue Radiation Sensitivity
why cancer risks at low doses are uncertain
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. 
relative risk of a 1 in a million chance of death from activities common to our society
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)
slide28

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?:

more problems
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?
slide30
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
slide31

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

slide32

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
slide33

If during an Nephrostrogram exam using 80 kvp –

  • the Primary tube current output @1 ft was 2 R/mA/min
  • the fluoro tube operated at 0.5 ma.
  • What is the TUBE OUTPUT? _________/min
  • The RT received 150 mr/hr
  • of scatter @ 2 foot from the patient for 10 min
  • then moved 8 feet from the patient for another 10 min.
  • Answer for the following DOSE & Units
  • What was the total Fluoro time? _____________
  • WHAT WAS THE TOTAL EXPOSURE TO THE
  • PATIENT ________
  • TECHNOLOGIST _________________
slide34

Two of the most radiosensitive

tissues with rapidly dividing cells

in the body is ____ tissue.

Which one is most SENSITIVE

cells most sensitive
CELLS MOST SENSITIVE

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

  • 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
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
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
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