1

Calculating pt doseUsing 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

• 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.

2

• 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

3

4

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.

5

From RHB Syllabus6

• 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

7

• “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?

•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 5.5 x 5mas = 27.5 mRad

• Lat 5.5 x 20 = 110 mRad

• This does not take in account SSD for ESE

•LOOK AT CHART: mr/mas

• 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

10

11

Find the mr/mas

• 100 kvp

• 400ma 0.10s = 150mR –

• what is the mr/mas?

12

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

13

• “AVE” L.SP EXPOSURE - 5 IMAGES

• (Ave – Pt meas 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

14

15

• “AVE” CHEST EXPOSURE - 2 IMAGES

• (Ave – Pt meas 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

16

17

ExaminationTechnique (kVp/mAs)

Entrance Skin Exposure (mR)

Mean Marrow Dose (mrad)

Gonad Dose (mrad)

Skull 76/50 200 10 <1

Chest 110/3 10 2 <1

Cervical spine 70/40 150 10 <1

Lumbar spine 72/60 300 60 225

Abdomen 74/60 400 30 125

Pelvis 70/50 150 20 150

Extremity 60/5 50 2 <1

CT (head) 125/300 4000 20 50

CT (pelvis) 125/400 2000 50 2000

CT, Computed tomography.

18 BUSHONGTABLE 37-1 Representative Radiation Quantities From Various Diagnostic X-ray ProceduresPage 566 10TH ed

19Tissue and Cell Sensitivity to

Radiation

20

Tissue Radiation Sensitivity

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

• Least sensitive:• Bone and teeth• Muscle• Nervous system

21

Effects of Overdose to Humans

22Effects of Acute Radiation Exposures in Humans

23Why 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. 

24

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

25

TABLE 3-3 Organ or Tissue Weighting Factors

26

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)

27

• 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?:

28

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?

29

30

• 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

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

31

• 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

32

33 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 _________________

a. Spinal b. Muscle c. Skin d Thyroid

34

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

35

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

36

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

37

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  

38

39