1. Many safety features are designed into the modern equipment.
Chapter 39 Designing for Radiation Protection and Chapter 40 Radiation Protection
Many radiation protection devices and accessories are associated with a modern radiology service. Two of these common to all x-ray machines are:
Protective Tube Housing
The Control Panel
Many safety features are designed into the modern equipment.

2. Protective Tube Housing
Every x-ray tube must be contained within a protective housing to reduce leakage during operation.
The limit or leakage is less than 100 mR/hour.

3. Control Panel
The control panel must indicate the conditions of the exposure and positively indicate when the tube is energized.
Indications include:
mA, time or mAs
kVp
Focal Spot
A visible and audible signal that the tube is energized.

4. Source to Image Receptor Distance
A source to image receptor (SID) indicator must be provided.
It may be as simple as a ruler attached to the collimator.
It may be a ruler attached to the rails for horizontal and vertical tube movement.
It may be lights attached to the receptor or locks that prohibit exposure unless the SID is correct.
The SID indicator must be accurate to 2% of the SID.

5. Collimation
The unit should be equipped with a light localized, variable-aperture rectangular collimator.
Cone or diaphragms may be used in specialized machines.
Collimation must be accurate to 2% of the SID.
Some machines will have automatic collimation called PBL Positive Beam Limitation. It was required from 1974 to 1994 and still seen on many machines.

6. Beam Alignment
Each x-ray tube should have a mechanism to ensure that the tube is properly aligned to the image receptor.
It would do no good to align the light and beam if the film is not aligned.

7. Filtration
All general purpose x-ray units operated at 70 kVp or above must have at least 2.5 mm of Al filtration built into the unit.
Units operated between 50 and 70 kVp must have 1.5mm of Al filtration.
Below 50kVp 1.0 mm Al is required
Mammography tube have 30 µm of Mo or 60 µm of Rh.

8. Reproducibility
The out put radiation intensity should be constant from one exposure to another using the same factors.
Checked my making multiple exposures and observing the variation of intensity.
The variation can not exceed 5%.

9. Linearity
When adjacent mA stations are used such as 100 mA or 200 mA and the time is adjusted the intensity should remain the same.
When the time is changed, the change should be proportional.
The linearity of exposure should be within 5%.

10. Operator Shield
It should not be possible to make an exposure with the operator outside the operator shield or control booth.
The exposure button should be attached to the control panel and not on a long cord.
We use Dead man type switches that require two fingers to make the exposure.

11. Fluoroscopic Equipment
Since fluoroscopic equipment is beyond the chiropractic standards in California we will not cover all the protective devices in fluoroscopic machines. They include
Lead shields
Collimators
Exposure Controls
Bucky slot cover
Cumulative Timer

12. Design of Protective Barriers
When designing a radiographic room a number of factors must be addressed besides the architectural features.
Machine location
Range of movement of tube and tube direction
Use of adjoining rooms
Which floor you are on.

13. Design of Protective Barriers
Great attention must be given to the location of the equipment.
Often necessary to add a protective barrier lead sheets or other construction materials placed in the walls of the examination room.
They may even be required in the floor and rarely in the ceiling.
A medical physicist must be consulted to determine shielding requirement for the room.

14. Types of Radiation
The protective barriers must account for tube leakage, the primary beam and scatter radiation.
Primary radiation is most intense so it requires the greatest shielding.

15. Primary and Secondary Barriers
For erect radiography, the receptor is mounted to the wall. This wall and any wall that the primary beam can be directed are considered primary protective barriers.
The other walls are considered as secondary protective barriers. Tube leakage and the patient are the primary source of exposure to these walls.
The patient is the single most important source of secondary radiation.
The intensity of the scatter is about 0.1% of the primary beam at the patient.

16. Shielding materials
Usually lead sheets bonded to sheetrock or wood paneling are placed in the walls for primary protective barriers.
Such materials are available in various thickness as is specified to the architect and contractor in pounds per square foot.
Construction materials such as concrete block or brick can be used instead of lead.

17. Lead and Concrete Equivalentsmm in
Lb/ft2 cm
0.4
1/64 1
2.4
1 3/8
0.8
1/32 2
4.8
1 7/8
1.2
3/64 3
7.2
2 7/8
1.6
1/16 4
9.6
3 3/4

18. Secondary Protective Barriers
The walls that are away from the tube direction are secondary barriers. The exposure comes from tube leakage and the patient.
Barriers designed to shield secondary radiation are called secondary protective barriers. They are always less thick than primary barriers.
Often lead is not required depending upon the distance from the tube. Steel, glass gypsum or wood may be adequate.

19. Control Booth
Ideally the control booth is located so the primary beam can not be directed toward the control booth. In this case, it is a secondary protective barrier. Four thicknesses of gypsum and ½” thick glass may be adequate.
If the tube can be directed toward the control booth as at the college, the wall facing the tube is a primary barrier.

20. Equivalent materials for secondary barriers
Lead
required
Steel
(mm)
Glass
Gypsum
Wood
0.1
0.5
1.2
2.8 19
0.2
2.5
5.9 33
0.3
1.8
3.7
8.8 44
0.4
4.8 12 53

21. Factors Affecting Barrier Thickness
Distance The distance from the source of radiation greatly impacts the thickness of the barrier.
Wall and floor mounted tube stands require more shielding on the attaching wall due to protection from tube leakage.
Ceiling suspended systems often have the table in the center of the room so no single wall is subjected to especially intense radiation.

22. Factors Affecting Barrier Thickness
Occupancy The use of the area protected is of principle importance. A closet or storeroom would need less shielding than an office or laboratory occupied 40 hours per week.
This reflects the time of occupancy factor that was established by the NCRP.

23. Factors Affecting Barrier Thickness
Controlled area: Design limits for controlled access areas are based upon the annual recommended dose limits of 5000 mrem/year. The weekly limit for exposure to personnel in the space is less than 100 mrem per week.
Controlled area are occupied by monitored radiology personnel and patients only.
Uncontrolled area: An uncontrolled area can be occupied by anyone. Exposure limits are based upon the public DL of 2 mrem/wk or 2.5 mrem in any hour.

24. Factors Affecting Barrier Thickness
Workload: The volume of radiographic examinations must be factored. Busy rooms require more shielding that infrequently used rooms.
This characteristic is called Workload (W) and units of measure of milliampere-minutes per week (mAmin/wk).

25. Factors Affecting Barrier Thickness
Use Factor: The percentage of time the tube is on and directed toward a particular wall is called the use factor.
For conventional x-ray the floor is rated as 1 and each wall as ¼.
Rooms with a wall Bucky has the wall behind the Bucky as 1. All others would be considered as zero for primary protection so they are secondary barriers.
Ceiling are almost always considered as secondary protective barriers.

26. Factors Affecting Barrier Thickness
kVp: The final consideration in the design of an x-ray protective barrier is the penetrability of the x-ray beam. kVp is the factor for penetration.
100 kVp is used for general radiology rooms and 30 kVp for mammography.

27. The final result
Measurements taken outside the room always results in radiation levels far below the calculated exposure. The use of 100 kVp is high since most exposure are in the 75 kVp range.
The calculation are intended to result in exposure limits of 100 mrem/wk in the room and 2 mrem/wk outside the room. Rarely will the exposure exceed 1/10 of the DL.

28. Radiation Detection and Measurement
There are instruments designed to detect radiation or to measure radiation or both.
Those designed to detect usually operated in a pulse or rate mode and are used to detect the presence of radiation.
They will chirp or tick when radiation is detected.
The response measurement is in mR/hr or R/hr.

29. Dosimeters
Units that measure the intensity of radiation are called dosimeters. They operate in the integrate mode where they accumulate the exposure and respond to the total exposure.
The response is in mR or R.
The earliest dosimeter was the film badge. It is still popular today though there are some newer technologies that have some better characteristics.

30. Dosimeters Types of Dosimeters Film Badge (photographic emulsion)
Gas filled detectors
Ion Chambers
Geiger-Muller Counter
Proportional Counters
Thermoluminescence dosimeter (TLD)
Optically stimulated dosimeter (OSL)
Scintillation detector

31. Film Badges Limited range < 10 mR not measured. Energy Dependent
Must be changed monthly
Popular for personnel monitoring
Must be worn with proper side to exposure.
Sensitive to heat never leave in a car.
Sensitive to humidity and water.

32. Gas-Filled Detectors
Can measure a wide range of radiation intensities from 1 mR/hr to several thousand r/hr.
Used to assay radionuclides in nuclear medicine.

33. Gas-Filled Detectors
The ionization of gas is the basis for gas filled detectors.
They are used as laboratory instruments and meters to detect very low radiation intensities.

34. Thermoluminescence Dosimeter (TLD)
Some materials glow when heated. This is referred to as thermoluminesecence.
Some materials will glow brightly after exposure to ionizing radiation and subsequently heated.
This is the principle of operation of the TLD. Discovered in the 1960 at the University of Wisconsin.

35. TLD
After irradiation, the TLD phosphor is placed on a special dish or plancet for analysis in the analyzer.
The analyzer is light tight and temperature controlled.
A PM tube is used to read the exposure.

36. TLD Lithium fluoride is most commonly used TLD material.
It is relatively sensitive and can measure doses as low as 5 mrad with modest accuracy and at exposures greater then 10 rad is accurate to better than 5%.
Calcium Fluoride activated with manganese is more sensitive and can measure less than 1 mrad. Used for environmental monitoring.

37. TLD
TLD’s have the several benefits as personnel monitors compared to film badges.
They are reusable
More accurate
Not sensitive to heat or humidity
Can be changed less frequently i.e. quarterly

38. Optically Stimulated Luminescence (OSL)
Developed in the late 1990’s by Landauer, Optically Stimulated Luminescence uses aluminum oxide at the radiation detector.
The irradiation of Al2O3 stimulates some electrons to an excited state.

39. Optically Stimulated Luminescence (OSL)
During processing, laser light stimulates these electrons to an excited state and returning them to ground state with the production of light.
Works similar to TLD but far more accurate.

40. OSL OSL is superior to TLD and Film Badges because:
Accurate to 1 mrad within +/-1 mrad.
Reanalysis is possible to confirm report.
Gain qualitative information about exposure conditions.
Wide range
Long Term stability

41. Scintillation Detectors
Scintillation detectors are the basis of nuclear medicine gamma cameras used for bone scans.
Scintillation detectors are used in computed tomography scanners.
Scintillation detectors are more sensitive than Geiger-Muller dosimeters.

42. Scintillation Detectors
The crystal emittes light proportional to the energy of the absorbed radiation.
The 50 keV exposure is totally absorbed and produces 50 units of light.
The second exposure produced 30 keV of Compton scatter and 20 units of light
A PM tube captures the light.

43. Chapter 40 Radiation Protection Procedures

44. Occupational Radiation Exposure
Radiation dose is measured in units of rads (GyT).
Radiation exposure is measured in Roentgens (GyA).
When the radiation exposure is to a chiropractor, radiologic technologist or radiologist, the proper unit is rem (Sv).

45. REM (Sv)
The rem is the unit of effective dose and is used for radiation protection purposes.
The terms exposure, dose and effective dose have precise and different meanings but they are often used interchangeably in radiology because they have approximately the same numeric value.
The rem (Sv) identifies the biologic effectiveness of the radiation energy absorbed.

46. Recommended Dose
The recommended dose for radiology radiation workers is 50 mSv/year (5000 mrem/year).
Studies have shown that 88% receive less than 1 mSv/year (100 mrem/year).
53% receive less than the detectible dose.
0.05% receive more than 50 mSv/year.

47. Recommended Dose
Medical radiologist typically receive more radiation exposure than technologists due to fluoroscopy and being closer to the source of radiation.

48. Fluoroscopy
Fluoroscopy is the primary source of the highest occupational exposure.
Personnel in the room during the examination must wear protective aprons.

49. Fluoroscopy
The lead apron and how the tube is placed will have a great impact on exposure during fluoroscopy.
Radiologist and personnel doing interventional examinations should also wear extremity monitoring.

50. Computed Tomography
The operators area in computed tomography is safe. There is exposure in the scanner room so aprons should be worn when in the room during scanning.

51. Mobile radiography
The use of portable c-arm fluoroscopy results in exposure for other personnel in the area during the examination.
The exposure is so low that normally monitoring is not required for nursing personnel unless they are frequently involved in these examinations.
The operator will receive the same exposure or higher exposure compared to stationary fluoroscopy.

52. Mobile radiography
Mobile x-ray is a hazard for the technologist operating the machine but typically not for other personnel.
The operator must wear protective lead aprons and stand as far away from the tube as possible.

53. Patient Dose
The exposure to patients to medical x-rays is commanding increased attention for two reasons.
The frequency of x-ray examinations is increasing among all age groups at about 10% per year in the United States.
Increased concerns among public health officials and radiation scientists regarding the risks associated with medical exposure.

54. Increased use of x-ray
Doctors are using x-ray more as a diagnostic tool.
X-ray diagnosis is considered to be more accurate than in the past. Training of radiology personnel and equipment improvements allow for more difficult but substantive examinations with greater accuracy.

55. Increased risks
More reports of superficial tissue damage from interventional radiology are common.
Increased use of computed tomography.
Increased concerns about possible late effects of diagnostic exposures means that attention must be given to good radiation control practices. When exams can be obtained with lower dose, it should be because of the reduced risk. This is in keeping with ALARA.

56. Estimation of Patient Dose
Patient exposure to diagnostic x-rays is usually reported in one of three ways.
The exposure to the entrance surface or entrance skin exposure is most often reported because it is the easiest to measure.
The Gonadal Dose is important because of the possible genetic response to medical x-rays. It is not difficult to estimate or measure.
The dose to the bone marrow is important because bone marrow is the target organ believed responsible for radiation induced leukemia. It can not be measured but is estimated from the ESE.

57. Entrance Skin Exposure
ESE is most often referred to as the patient dose. It is widely used because it is easy to measure and reasonably accurate estimates can be made in the absence of measurements.
TLD can be used to measure the ESE. Accurate to 5%
A nomogram can be used to estimate exposure. Accurate to perhaps 50%.
The third involves using a known out put intensity at given factors and distance.

58. Nomogram
To use the nomogram we need to know the total filtration of the machine.
This is available from the physicist’s annual or biannual report.
Draw a line perpendicular to the filtration to the kVp used for the examination.
Draw a right angle line to the point where the first line intersects the kVp.
This will tell the mR/mAs.
Multiply the mR/mAs time the mAs used to obtain the estimated exposure.

59. Nomogram
This type nomogram can be produced by the health physicist for each room.
It is very accurate.
A straight line between any kVp and mAs will cross the ESE line.

60. Mean Marrow Dose
The hematologic effects of radiation are rarely experienced in diagnostic radiology.
It is appropriate that we measure the patient dose during procedures.
The mean marrow dose is the average radiation dose to the entire active bone marrow.
If 50% of the marrow was exposed to 25mrad, the mean marrow exposure would be 12.5 mrad.

61. Distribution of Active Bone Marrow in Adults
Anatomic site
Head
Upper limb girdle
Sternum
Ribs
Cervical vertebrae
Thoracic vertebrae
Lumbar vertebrae
Sacrum
Lower limb girdle
% of bone marrow 10 8 3 11 4 13 29

62. Genetically Significant Dose
Measurement and estimates of gonad dose are important because of suspected genetic effects of radiation.
Although the gonad dose in diagnostic radiology is low for each individual, it may have some significance in terms of population.
The Population gonad dose of importance is the GSD, the radiation dose received by the gene pool.

63. Genetically Significant Dose
The GSD is the dose that, if received by every member of the population, would produce the total genetic effect on the population as the sum of the individual doses actually received.

64. Estimated GSD from Diagnostic X-ray Examinations
Population
Denmark
Great Britain
Japan
New Zealand
Sweden
United States
GSD 22 12 27 72 20

65. GSD for United States
The genetic radiation burden is over and above the natural background radiation level of about 100 mrad/year. The genetic effects of the total of 120 mrad/year are not detectable.
There have been no detectable genetic effects to radiation in humans.

66. Patient dose in Special Imaging
There are two areas of special imaging that are important sources of patient exposure are:
Mammography
Computed Tomography

67. Mammography
Because of the considerable application of x-rays for the examination of the female breast and the concern for the induction of breast cancer from radiation we must have some understanding of the doses involved.
There are two forms of mammography used today: screen-film and digital mammography.

68. Mammography
Mammography is done using 26 kVp with an ESE of about 800 mR/view. Increasing kVp degrades the image.
The only way we could lower exposure is with faster films and screens.
Radiographic grid ratios of 4:1 or 5:1 are used for most screen film mammograms.
Compression is used to equalize density and reduce exposure.

69. Mammography
Patient exposure is measured in Glandular Dose. Glandular dose is about 15% of the ESE.
The glandular dose should not exceed 100 mrad/ view with contact mammography and 300 mrad/view with a grid.
The concern comes from the number of examinations that a women will experience during her lifetime.

70. Computed Tomography
There are two consideration when we discuss radiation dose and computed tomography.
Entrance Skin Dose will always be much higher than radiography
Distribution of dose to the internal organs.
Lets look at a typical non-spiral head CT.
The ESE will be much higher for the contiguous CT sliced compared to a single radiographic exposure.
The Radiographic exam of the skull often involves four or more exposures.
The CT exam is the total exposure and it usually has less volume of tissue irradiated.

71. Computed Tomography
The increasing use of spiral or multislice CT, CT must often be considered a high dose procedure.
The USPHS suggests that 5% of all radiographic exams are CT but they constitute 35% of the total population dose. The CT dose is about equal to the average fluoroscopy dose.

72. Computed Tomography
Radiography is like a flash photograph where the patient is floodlighted by the x-rays to exposure the image receptor.
Computed Tomography use a finely collimated beam of x-rays. This makes the dose distribution different from radiography.
The CT dose is uniform though out the exposure and about 50% at midline.
For radiography and fluoroscopy the entrance dose is high but the exit dose is low.

73. Computed Tomography
The reason for the dose efficiency of CT arises because of precise collimation of the beam.
Scatter increases patient exposure and reduces contrast.
The CT uses a narrow, well-collimated beam, scatter is reduced and contrast resolution improved. Thus a larger percentage of the beam contributes usefully to the image.

74. Computed Tomography
The precise collimation means that only a well defined volume of tissue is irradiated for each image.
The ideal beam would have sharp edges with no overlap. The dose delivered to the patient from a series of contiguous CT images would be the same as one single image.

75. Computed Tomography The ideal is not possible in current practice.
Focal spot blurs the boundaries of the beam.
The beam is not perfectly parallel
The couch movement is not perfect.
If the pre-patient collimator is too wide, tissues near the interface is double exposed.
The result is some tissue is double exposed.

76. Computed Tomography Collimator accuracy must be evaluated frequently.
Spiral CT is a problem for dose calculations. The pitch or the rate of movement of the couch during the scan greatly impacts exposure.
Remember pitch is the patient movement/360º/ beam width.
1.0:1 would be the same as normal CT but with a wider beam width.
A higher pitch would reduce exposure while a lower pitch would increase exposure.

77. Computed Tomography
With all forms of radiographic imaging, Image noise reduced image quality.
Noise is the result of not enough photons. Therefore to reduce noise, the exposure must be increased.
Thinner slices also results in increased exposure.
The challenge is producing adequate image quality with the lowest possible exposure.

78. Representative ESE from Various Exams
Factors (kVp/mAs)
ESE (mR)
Mean Marrow
Gonad Dose
Skull
76/50
200 10
<1
Chest
110/3 2
C-spine
70/40
150
LSSP AP
72/60
300 60
225
Extremity
60/5 50
CT Head
125/300
3000 20
CT Pelvis
124/400
4000
100

79. Dose Calculations for PCCW Examinations
The following spreadsheets are estimated exposures for common radiographic examinations performed in PCCW clinics.
Factors used are the factors used in Room One in the Tasman clinic and the follwing patient measurements.
Cervical spine: AP: 12 cm Lateral 12 cm
Thorax: AP: 23 cm Lateral: 31
Lumbopelvic: AP: 23 cm Lateral: 31

80. Patient Exposure for Typical Cervical Spine Examinations
Series
Lateral AP
APOM
Oblique (2)
Total mrad
Ltd
3 views
25.9
63.9
94.7
184.5
5 view with oblique views
127.2
311.4
5 view with flex & ext laterals
77.7
236.3
7 views Davis Series
363.2

81. Patient Exposure for Typical Thorax Examinations
Series
AP/PA
Lateral
Oblique
Total mrad
Thoracic spine
424.5
791.9
1216.7
Chest 2 view
16.8
42.6
59.4
Upper ribs
162.6
188.4
351
Lower ribs
462.4
525.0
987.4

82. Patient Exposure for Typical Lumbar Spine Examinations
Series
Lateral
AP/PA
Sacral Base AP
Oblique (2)
Total mrad
Ltd 2 views
1606.8
503.1
2109.9
Ltd with oblique views
1218
3327.9
Complete 5 views with AP Sac Base
609
3936.9
Ltd with AP Sacral Base
2718.9

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