SIAPA ITU RADIOGRAPHER?

Secara ringkasan Radiographer atau nama lain yang mudah untuk dikenali Juru x-ray adalah petugas yang berkelayakkan untuk mengendalikan alatan radas sinaran .

Tugas seorang juru x-ray adalah luas, ia merangkumi pelbagai modaliti yang menggunakan sinar-x, seseorang juru x-ray juga seorang yang bertauliah untuk memberikan nilai dedahan sinar-x kepada pesakit mengikut kuantiti yang optimum dengan memberikan kualiti imej diagnostik yang boleh digunakan sebagai bahan bantu mendiagnosis penyakit.

Ini kerana pertimbangan mengikut keadaan dan penyakit perlu difikirkan sekali semasa menjalankan tugas, ini penting bagi memastikan pesakit menerima dedahan yang secukupnya tanpa memerlukan pengulangan semula dan imej yang dihasilkan memberikan nilai diagnostik yang secukupnya.

Juru-ray dibahagikan kepada 2 bahagian atau kepakaran iaitu Diagnostik dan Terapi, implementasi adalah sama tetapi perlaksanaan kepada mesin adalah berbeza-beza.

Juru x-ray Diagnostik

• General x-ray
• Fluoroskopi
• X-ray Mudahalih
• Angiografi
• CT scan
• Magnetic Resonance Imaging (MRI)
• Mammografi

Juru x-ray Terapi

• LINAC (linear accelarator)
• Gamma Camera

apa yang penting pengamalan dan etika dalam mengendalikan alatan sinaran adalah penting bagi memastikan pesakit yang didedahkan dengan sinar x selamat.

APA ITU RADIASI

Radiation
What is radiation?
Radiation: is the transfer of energy in the form of particles or waves.
Energy: the ability to do work (Force·Distance)
X-rays are electromagnetic radiation. Electromagnetic radiation is a form of pure energy which is carried by waves of photons. Electromagnetic radiation is also known as light.  Visible light, Radio and X-rays are all forms of electromagnetic radiation which vary in energy and thereby wavelength and frequency as well (Figure 1-1).   
Figure 1-1: Forms of Electromagnetic Radiation
Courtesy of Phil Rauch and Laura Smith, 2000  

Ionizing Radiation
X-ray radiation contains more energy than ultraviolet, infrared, radio waves, microwaves or visible light.  X-ray radiation has sufficient energy (>30 eV) to cause ionizations.  An ionization is a process whereby the radiation removes an outer shell electron from an atom (Figure 1-2).
Figure 1-2: The Ionization Process
Alan Jackson, 2001

Non-ionizing radiation does not contain sufficient energy (30 eV) to cause ionizations (Figure 1-3). While some non-ionizing radiation can be harmful, the ionization process is clearly able to cause chemical changes in important changes to biologically important molecules (e.g. DNA). 
Figure 1-3: Non-Ionizing Radiations
Courtesy of Alan Jackson, 2001

X-ray Production

X-rays are produced when high velocity electrons are decelerated (slowed or stopped) or by a nucleus of an atom especially by high atomic number material, such as the tungsten target (anode) in a X-ray tube. An electrically heated filament (cathode) within the X-ray tube generates electrons that are accelerated from the filament to the tungsten target by the application of a high voltage to the tube.  The energy gained by the electron is equal to the potential difference (voltage) between the anode and cathode.   This electron energy is typically expressed in kilovolts (kV).  The accelerated electron interacts with the target (anode) nucleus.  As the electric field of the electron interacts with nucleus, the electron releases energy in the form of X-rays.  This method of of x-ray production is called bremsstrahlung or braking radiation (Figure 1-4).
FIgure 1-4: X-ray Production (Bremstrahlung)
Courtesy of the University of Michigan Student Chapter of the Health Physics Society

Since the degree of interaction of the accelerated electron with the target nucleus can vary, the energy spectrum, or distribution of energy, of the X-rays produced by the bremsstrahlung process is continuous.  
As smaller number of characteristic x-rays are also produced as excited electrons interact with the electrons of the target atoms.  The X-rays produced from this interaction, with a given orbital electron, have a single specific energy (discrete) instead of a continuous spectrum.  Mammographic x-ray tubes are designed to maximize characteristic production to optimize breast tissue imaging.  The amount of characteristic X-rays in a fluoroscopy beam is relatively low. 
The lower energy X-rays are absorbed within the X-ray tube.  This reduces the number of lower energy X-rays in the resultant spectrum since the lower energy X-ray are less penetrating. The beam is considered "harder" when there is more filtration.  Most X-ray manufacturers add filtration, commonly consisting of aluminum, since lower energy X-rays do not contribute to images and add to patient dose.
The resulting x-ray spectrum energy (Figure 1-5) is a mixture of the characteristic and bremsstrahlung radiation, less the primarily low energy X-rays absorbed by the X-ray tube (and added filtration).  The maximum energy of the X-ray produced is equal to the maximum potential applied across the x-ray tube.  This peak X-ray energy is usually described with the unit kVp (kilovolt peak or kilovolt potential).  The type of target anode, potential (kVp) and added filtration produce a beam of a given "quality" which implies specific shape of an X-ray spectrum.
Figure 1-5: Simplified X-ray Spectrum
Alan Jackson, 2001

X-ray Machine Parameters
The quantity  of electron flow (current) in the X-ray tube is described in units of milliamperes (mA). The rate of X-ray production is directly proportional to the X-ray tube current. Higher mA values indicate more electrons are striking the tungsten target, thereby producing more X-rays. The voltage (kVp) primarily determines the maximum X-ray energy produced but also influences the number of X-rays produced. Increasing the kVp attracts more electrons from the filament increasing the rate of X-ray production. However, this relationship is not directly proportional but higher kVp setting will result in a substantial increase in the number of X-rays produced.  The total number of X-rays produced at a set kVp depends directly on the product of the mA and exposure time and is typically described in terms of mA-s or mAs. Fluoroscopy is usually performed using 2 to 5 mA current at a peak electrical potential of 75 to 125 kVp.
X-ray Production Efficiency and Heat Loading
The production of x-rays is a relatively inefficient process so that only a small fraction of the energy imparted by the decelerating electrons is converted into X-rays. The remaining energy is converted to heat. Thus, the production and dissipation of heat in the X-ray tube is a serious consideration.  Thus, most x-ray machines have rotating anodes to spread out the heat to prevent anode melting.  This is the reason why you can hear an X-ray machine make noise. Most fluoroscopic x-ray machine anodes are primarily based on tungsten due to tungsten's high melting point, excellent heat transmission, and high atomic number.  In spite of tungsten's favorable qualities, with sufficiently high usage, X-ray production is prevented by the system to protect the tube. Substantial improvements have been recently made in the ability of fluoroscopic X-ray equipment to remove waste heat and thereby maintain high beam outputs.
Figure 1-6: Heat Production
Courtesy of: Phil Rauch and Laura Smith, 2000


Divergent Nature of X-ray Radiation

Once generated, the X-rays are emitted in all directions in a uniform manner (isotropically). The lead housing surrounding the X-ray tube limits X-ray emission through a small opening or port in the X-ray tube. The resulting primary beam of useful radiation is shaped by additional lead shutters, or collimators, that can be adjusted to provide different beam shapes or sizes.  
Inverse-Square-Law (Radiation intensity with distance)
Since the initial beam travels in straight but divergent directions, geometry in a three dimensional world dictates that the radiation intensity will decrease with the inverse square of the distance. Consequently, the number of X-rays traveling through a unit area decreases with increasing distance. Likewise, radiation level decreases with increasing distance since exposure is directly proportional to the number of X-rays interacting in a unit area. The intensity of the radiation is described by the inverse square law equation:

Where X_A is the radiation exposure rate at distance D_A   compared with the exposure rate (X_B) at some other distance (D_B).  
This effect is shown graphically in Figure 1-7:
Figure 1-7: Inverse Square Law
Courtesy of Scott Sorenson, 2000

1-Meter Distance: 1,000 X-rays pass through a
unit area. The amount of X-rays per unit area is
1,000.

2-Meter Distance: With increasing distance, the
beam diverges to an area 4 times the original area.
The same 1,000 X-rays are evenly distributed
over the new area (4 times the original). Thus the
amount of X-rays per unit area is 250 or 1/4 the
original. The resulting radiation exposure is 1/4
less.
This relationship indicates that doubling the distance from a radiation source decreases the radiation level by a factor of four. Conversely, halving the distance, increases the radiation level by a factor of four.  Intelligent application of inverse square law principles can yield significant reductions in both patient and operator radiation exposures.

Example 1:

An operator normally stands 1 meter away from the patient during cineangiography. The exposure rate at this point is 15 mrem/min (this unit will be explained later) and total cineangiography time is 2 min. What is the reduction should the operator stand 1.2 meters away?

Solution 1:

The original exposure was 30 mrem (15 mrem/min for 2 min). The new exposure would be:



A 31% percent reduction in radiation exposure is achieved in this example.
X-rays Interactions with matter

X-rays have several fates as they traverse tissue. These fates fall into 3 main categories (Figure 1-8):
Figure 1-8: X-ray Interaction-Imaging Considerations
Courtesy of Scott Sorenson, 2000


No interaction: X-ray passes completely throughtissue and into the image recording device. Producing an image
Complete absorption: X-ray energy is completely absorbed by the tissue. This produces radiation dose to the patient. 
Partial absorption with scatter: Scattering involves a partial transfer of energy to tissue, with the resulting scattered X-ray having less energy and a different trajectory. This interaction does not provide any useful information (degrades image quality) and is the primary source of radiation exposure to staff.
X-ray Interaction with Matter
The probability of X-ray interaction is a function of tissue electron density, tissue thickness, and X-ray energy (kVp). Electron dense material like bone and contrast dye attenuates more X-rays from the X-ray beam than less dense material (muscle, fat, air). The differential rate of interaction provides the contrast that forms the image. 
Tissue Electron Density Interaction Effects:  
As electron density increases, the interaction with X-rays substantially increases. Higher atomic number materials have increased electron density.  Thus, bone, which is substantially comprised of calcium, produces more attenuation, than tissue, which is comprised of carbon, hydrogen and oxygen (all of which have a lower electron density or atomic number than calcium).  Thus, the image of bone and soft tissue has contrast, or difference, between bone and soft tissue.
The concept of contrast and electron density X-ray interaction can be shown in Figure 1-9.  
Assume 1,000 X-rays strike the following body portions. The number of X-rays reaching the recording media (film, TV monitor) directly effect the image's brightness. 
Figure 1-9: Electron Density and Image Contrast
Courtesy of Scott Sorenson, 2000

In this example, 900 X-rays are capable of penetrating the soft tissue, while only 400 penetrate the bone (Higher electron density compared with soft tissue). The contrast between the bone and soft tissue is (900-400)/900 = 0.56.

PERLINDUNGAN DARIPADA SINARAN LUAR

External Exposure Protection
X-ray machines do not produce internal radiation exposure like radioactive materials.  There are three basic protection methods for external sources of radiation: Minimizing exposure time, maximizing distance from the X-ray tube, and the utilization of shielding.

Minimizing Exposure Time: Reduce "Beam-on-time"

Radiation exposure during fluoroscopy is directly proportional to the length of time the unit is activated. Reductions can be realized by:
 

1. Not exposing patient while not viewing the TV image;
2. Pre-planning images. An example would be to ensure correct patient positioning before imaging to eliminate unnecessary "panning;" 
3. Avoiding redundant views;
4. Operator awareness of the 5-minute time notifications. 

Fluoroscopy’s real-time imaging capabilities are invaluable for guiding procedures or observing dynamic functions. However, there is no advantage over conventional X-ray techniques when viewing static images. Use of Last-Image-Hold features, when available, allows static images to be viewed without continuously exposing patient and operator to radiation.

Human eye integration time or recognition time of a fluoroscopy image is approximately 0.2 seconds. Therefore, short "looks" usually accomplish the same as a continuous exposure. Prolonged observation will not improve the image brightness or resolution (Seifert 1996).

Maximize Distance

A small increase in the operator's distance from the patient can significantly reduce the  operator's exposure.  Standing one step further away from the patient can cut the physician's exposure rate by a factor of 4 (AAPM 1998) (Figure 5-1). You should periodically self-evaluate you personal technique to identify whether opportunities to increase distance exist.
Figure 5-1: Benefit of Increasing Distance
Courtesy of Sorenson, 2000.


In percutaneous transluminal techniques, using the femoral approach rather than the brachial approach yields distance benefits to the operator (Figure 5-2).
Figure 5-2: Influence of Technique
Courtesy of Sorenson, 2000.
 

Substantial increases in operator distance may be realized through remote fluoroscopy activation whenever automated contrast injectors are used.

Many procedures require staff to intermittently interact with the patient near the fluoroscopy system. The operator can reduce staff exposure by delaying fluoroscopy until these activities are completed and/or by alerting these personnel when imaging; especially during high dose rate modes like cineangiography (Figure 5-3).
Figure 5-3: Benefit of Alerting Staff
Courtesy of Sorenson, 2000.



Room Lighting

Provisions should be made to eliminate extraneous light that can interfere with the fluoroscopic examination. Room lighting should be dim to enhance visualization of the image. Excessive light can decrease the ability of the eye to resolve detail. Measures taken to improve detail often involve increasing patient/staff exposure.

X-ray Tube Position

Fluoroscopy examinations have the smallest operator exposure when the X-ray tube is underneath the examination table (Figure 5-3). Whenever possible, the operator should avoid the X-ray tube side of the table when imaging oblique or lateral images.
Figure 5-3: Benefit of Under-Table Position
Courtesy of Sorenson, 2000.

Note: The benefit is exaggerated-some operator dose occurs on the I-I side.
I-I to Patient Air Gap

The operator must be aware of the  X-ray tube-to-patient distance. Positions closer can lead to extremely high patient exposures due to Inverse-Square-Law effects (case study). Minimizing the air gap between the I-I and the patient typically ensures that this distance is maintained. Use of the separator or spacer cone can prevent serious effects. The spacer cone is a spacer attached to the tube housing designed to keep the patient at a reasonable distance from the x-ray source. This is done specifically to avoid the high skin-dose rates that can be encountered near the tube port. Spacer cones protect patients from extremely high local exposures by making it physically impossible to get too close to the X-ray source (inverse-square law effects). For some X-ray machines, the spacer cone is designed to be removable (Figure 5-3) in order to provide more flexibility in positioning for some special surgical procedures (e.g., portable C-arms). There is a risk of very high dose rates to the skin surface when it is removed.
Figure 5-3: Removable Spacer Cone
Courtesy of Rauch, 2000

Reduce Air Gaps
Keeping the I-I as close to patient’s surface as possible significantly reduces patient and operator exposures (Figure 5-4). The I-I will intercept the primary beam earlier and allow less scatter to operator and staff. In addition, The Automatic Brightness Control (ABC) system would not need to compensate for the increased X-ray tube to I-I distance caused by the air gap. The presence of an air gap will always increase patient/operator radiation exposure and decrease image quality.
Figure 5-4: Benefit of Reducing the Air Gap (I-I  Close to Patient)
Courtesy of Sorenson, 2000.

Care should be taken whenever the image view angle is changed during the procedure (e.g, changing from an ANT to a steep LAO). The I-I is often moved away from the patient while changing X-ray tube position. Large air gaps can result if the table or I-I height remains unadjusted.

I-I to Patient Distance Example:

After changing views, a 10-cm air gap between I-I and patient is inadvertently maintained. What is the increase in radiation exposure to a 20-cm thick patient positioned with the table 30 cm away from the X-ray source, assuming the ABC compensates by increasing mA only?
Note: mA only adjustments on ABC systems are reasonably common.

Solution:

Assuming the air gap could have been eliminated by moving the I-I closer, and that the brightness loss follows the inverse square law:





The brightness level with the air gap is only 69% of the zero air gap brightness. The ABC system compensates for brightness loss by producing 31% more X-rays. The exposure rate to the patient and staff is subsequently increased by 31%.


Reducing air gaps between patient and I-I also reduces image blur. Blurring of the image is caused by geometric magnification caused by air gaps. Gaps between patient and I-I enhance geometric magnification. The objects will appear larger with increasing gap size. However, note that image edges are more fuzzy (Figure 5-4). The degree of "fuzziness" will increase with increasing air gap.
Figure 5-4: I-I distance and Image Blur
Courtesy of Sorenson, 2000.

Courtesy of Sorenson, 2000.
Minimize Use of Magnification

Use of magnification modes significantly increases radiation exposure to patient, operator, and staff (See Chapter 3). Magnification modes should be employed only when the increased resolution of fine detail is necessary.

Collimate the Primary Beam

Collimating the primary beam to view only tissue regions of interest reduces unnecessary tissue exposure and improves the patient’s overall benefit-to-risk ratio. Optimal collimation also reduces image noise caused by scatter radiation originating from outside the region of interest (See Chapter 3). A good rule of thumb is that fluoroscopy images should not be totally "round" when collimators are available for use, the collimator edges should always be visible in the image.

Use Alternate Projections

Continuous exposure of the patient with the same projection (point of X-ray beam entry) can cause very high skin dose to small areas.  Thus, if the point of X-ray beam (projection) entry can be changed, the skin may be spared from the harmful effects of radiation.  While this is an effective protection method, care must be exercised to utilize this method intelligently since longer beam paths through the patient can cause higher patient and worker dose.
Steeply angled oblique images (e.g., LAO 50 with 30 cranial tilt) are typically associated with increased radiation exposure since: X-rays must pass through more tissue before reaching I-I. ABC compensates for X-ray loss caused by increased attenuation by generating more X-rays; Steep oblique angles are typically associated with increased X-ray tube to I-I distances. The ABC compensates for brightness loss caused by inverse square law effects by generating more X-rays. Oblique views may bring the X-ray tube closer to the operator side of the table, increasing radiation
exposure from scatter.
Operator exposure from different projections.
When possible, use alternate views (e.g., ANT, LAO with no tilt) when similar information can be obtained (Figure 5-5). The physician can reduce personal exposure by re-locating himself when oblique views are taken. For example, dose rates can be reduced by a factor of 5 when the physician stands on the I-I side of the table (versus X-ray tube side) during a lateral projection (AAPM 1998).
Figure 5-5: Physician Exposure for a variety of Projections
Courtesy of Sorenson, 2000.

Projections with the X-ray tube neutral or tilted-away from the operator are highlighted blue, while those tilted towards the operator are in red. Note the decrease seen between the LAO 40 views. The caudal tilt causes the tube to be more tilted away from the operator.

Optimizing X-ray Tube Voltage

Selection of an adequate kVp value will allow sufficient X-ray penetration while reducing the patient’s dose rate. In general, the highest kVp should be used which is consistent with the degree of contrast required (high kVp decreases image contrast).

Henry Ford Hospital has many resources available (e.g., Staff Radiologists, Medical Physicists) to assist the operator in optimizing the fluoroscopy image while minimizing patient exposure.

Use of Radiation Shields

Use of radiation shielding is highly effective in intercepting and reducing exposure from scattered radiation (Figure 5-6). The operator can realize radiation exposure reductions of more than 90 percent through the correct use of any of the following shielding options. Shields are most effective when placed as near to the radiation scatter source as possible (i.e., close to patient).

Many fluoroscopy systems contain side-table drapes or similar types of lead shielding. Use of these items can significantly reduce operator exposures. Many operators have had little difficulty incorporating their use, even during procedures requiring multiple re-positioning of the system.
Figure 5-6: Benefit of Hanging Shield
Courtesy of Sorenson, 2000.

Ceiling-mounted lead acrylic face shields should be used whenever these units are available, especially during cardiac procedures. Correct positioning is obtained when the operator can view the patient, especially the beam entrance location, through the shield.

Portable radiation shields can also be employed to reduce exposure. Situations where these can be used include shielding nearby personnel who remain stationary during the procedure.

Use of Personal Protective Equipment

Use of leaded garments substantially reduces radiation exposure by protecting specific body regions. Many fluoroscopy users would exceed regulatory limits should lead aprons not be worn. Operator and nearby staff (within 2 meters) are required to wear lead aprons whenever fluoroscopes are operated at Henry Ford Hospital.  Due to the poor material qualities of Leaded garments, proper storage is essential to protect against damage (Figure 5-6).  Whenever leaded apron are required, they must be supplied and paid for by your employer (Henry Ford Health System)
Figure 5-6: Properly Stored Leaded Garments
Courtesy of Sorenson, 2000.

Courtesy of Sorenson, 2000.

Lead aprons do not stop all the x-rays.  Typically at least a 80% reduction in radiation exposure is obtained by wearing a lead apron (Figure 5-7). It should be noted that the apron's effectiveness is reduced when more penetrating radiation is employed (e.g., the ABC boost's kVp for thick patients). Two piece lead apron systems are recommended for most users since they provide "wrap-around protection" and distribute weight more evenly on the user. Some aprons contain an internal frame that distributes some of the weight from the shoulders onto the hips much like a backpack frame. So called "light" aprons should be scrutinized to ensure that adequate levels of shielding are provided.  State of Michigan law requires the use of 0.5 mm lead equivalent aprons.
Figure 5-7:  Lead Apron Protection Efficiency
Courtesy of Sorenson, 2000.


Note that higher tube voltages sharply reduces the shielding benefits of lead aprons. Higher tube voltages will occur when imaging large patients or thick body portions. Also note that light aprons (0.25 to 0.35 mm Pb) provide less protection compared to the recommended 0.5 mm thickness.

Thyroid shields provide similar levels of protection to the individual’s neck region. Thyroid shield use is required for operators who use fluoroscopy extensively during their practice.

Optically clear lead glasses are available that can reduce the operator's eye exposure by 85-90% (Siefert 1996). However, due to the relatively high threshold for cataract development, leaded glasses are only recommended for personnel with very high fluoroscopy work loads (e.g., busy Radiology and Cardiology Interventionists). Glasses selected should be "wrap-around" in design to protect the eye lens from side angle exposures. Leaded glasses also provide the additional benefit of providing splash protection. Progressive style lenses for bifocal prescriptions are available from a limited number of manufacturers.

The latex leaded gloves provide extremely limited protection. Standard (0.5 mm lead equivalent) leaded gloves provide useful protection to the user’s hands.   However, trade-offs associated with use of 0.5 mm leaded gloves include loss in tactile feel, increased encumbrance and sterility. For these reasons, use of leaded gloves is left to the operator’s discretion. To minimize radiation exposure to the hands, the operator should:

1. Avoid placing his hands in the primary beam at all times;  
2. Place hands only on top of the patient. Hands should never be placed underneath the patient or table top during imaging; 
3. Consider using leaded gloves if hand placement within the X-ray beam is necessary or positioned nearby for extended periods of time.

Radiation Monitoring-Dosimeter Badges
Unlike many workplace hazards, radiation is imperceptible to human senses. Therefore, monitoring of personnel exposed to radiation is performed using a radiation dosimeter or "badge." Monitoring is useful to identify both equipment problems and opportunities for improving individual technique (ensuring radiation doses are ALARA). Monitoring also documents the level of occupational exposure.

The requirements for dosimetry has been determined by the Radiation Safety Committee for each work area.  These specify the types of dosimeters issued as well as the collection frequency. 
Some workers are issued a single whole body badge (black figure icon). This whole body dosimeter should be worn on the collar outside of any protective equipment worn (lead aprons). Readings from this position provide an estimate of the radiation exposure to the eyes. Dose estimates to the individual’s whole body are made using the appropriate algorithm. Other workers are issued multiple dosimeters.  These are designed to be worn as shown (Figure 5-8):
Figure 5-8:  Protective Devices
Lieto and Jackson, 2000.

Ring badge and Sterility
Infection Control has evaluated the use of ring badges in surgical arenas.  For open surgical theaters, ring badges are contraindicated.  Catheter procedures may be performed with ring badges.
Dosimetry Practices 

In order to provide an accurate estimate of personal risk, radiation badges are to be used at all times when working with radiation. It is also important to turn in the radiation badges on time. The accuracy of the readings depends on the timely processing of the dosimeter with the corresponding control dosimeters.
Absent dosimeters are taken very seriously by the institution.  Reports of which individuals have failed to properly return dosimeters (who did not report the loss of the dosimeter to the RSO) are sent to: the Radiation Safety Committee; the Department chairs; the Hospital Medical Executive Committee; and the Board of the institution.  To avoid this negative attention, turn your dosimeter in on time and promptly report the loss of a dosimeter to the Radiation Safety Office.  A new dosimeter will be issued at no cost and your good name will be preserved.

The Radiation Safety Officer (RSO) reviews dosimetry records on a monthly basis. Investigations of any exposure exceeding the established standards are performed to determine whether corrective action can eliminate or reduce exposures for all concerned. The circumstances surrounding most cases of excessive radiation exposures are often readily mitigated.

Radiation reports are provided annually to all monitored personnel employed or practicing at Henry Ford Hospital. In addition, monthly reporting of radiation exposure is available for highly exposed fluoroscopy users. Individuals can access their personal records at any time, and written dose estimates are provided upon request.

ALARA Philosophy

Regulatory dose limits should be viewed as the maximum tolerable levels. Since stochastic radiation effects, such as carcinogenesis, can not be ruled-out at low levels of exposure, it is prudent to minimize radiation exposure whenever possible. This concept leads to the As-Low-As-Reasonably-Achievable (ALARA) philosophy.

Simply stated, the ALARA philosophy requires that all reasonable measures to reduce radiation exposure be taken. Typically, the operator defines what is reasonable. The principles discussed in this manual are intended to assist the operator in evaluating what constitutes ALARA for his/her fluoroscopy usage.
The Henry Ford Hospital administration is committed to ensuring that radiation exposure to its medical staff and employees is kept ALARA. Full attainment of this goal is not possible without the co-operation of all medical users of radiation devices.
Summary of Fluoroscopy Safety

1. Keep beam ON-time to an absolute minimum!
2. Always use tight collimation!
3. Do not overuse the magnification mode.
4. Keep the image intensifier as close to the patient as possible, and the tube as far away from the patient as possible.  
5. Keep the kVp as high as possible considering the patient dose versus image quality. 
6. Keep tube current (mA) as low as possible. 
7. Minimize room lighting to optimize image viewing. 
8. Do not overuse the high dose rate. 
9. Personnel must wear protective aprons, use shielding, monitor doses and know how to position themselves and the machines for minimum dose. 
10. Change projections angle for long procedures to minimize local skin doses.
11. Remember that the X-ray output, patient dose, and area scatter levels increase for larger patients.

KESAN BIOLOGI DARIPADA RADIASI

  Biological effects of radiation

Most people know that radiation is potentially harmful to living systems, unfortunately there are a number of misconceptions about radiation biology which are perpetuated in popular culture. 
Radiation Biology History
 1895-Roentgen announces discovery of X-rays
1896-(4 months later) Reports of skin effects in x-ray researchers
1902-First cases of radiation induced skin cancer reported
1906-Pattern for differential radiosensitivity of tissues was discovered.
Relative Radiosensitivity of Tissue 
The relative radiosensitivity (sensitivity to radiation exposure) of a variety of tissue is shown in Figure 2-1 below:
Figure 2-1: Increasing Sensitivity to Radiation
Alan Jackson, 2001 from Seibert, 1996.

By 1906 Bergonie and Tribondeau realized that cells were most sensitive to radiation when they are:

• Rapidly dividing
• Undifferentiated
• Have a long mitotic future

Author Note: When DNA, which had not been discovered at this time,  has no backup (single strand).

Radiation sensitivity
Radiosensitivity is a function of the cell cycle with late S phase being the most radioresistant and G1, G2, and especially mitosis being more radiosensitive. 
Mechanisms of Radiation Injury
Radiation can directly interact with a molecule and damage it directly. Because of the abundance of water in the body, radiation is more likely to interact with water.  When radiation interacts with water, it produces labile chemical species (free radicals) such as  hydronium (H^.) and hydroyxls (^.OH).  Free radicals can produce compounds such as hydrogen peroxide (H₂O₂) which subsequently exert chemical toxicity.  The body has sophisticated protections against this type of chemical damage.  For example, this is why hydrogen peroxide foams when it is poured on a cut.  The hydrogen peroxide is being destroyed by an extremely rapid enzyme, hydrogen peroxidase.  
Nonetheless, while DNA and other repair methods are extremely capable of protecting the body, some fraction of the damage is not repaired or may be repaired incorrectly.  In either case, if the DNA is damaged, several things can happen. The most likely is that the damage will be repaired before the end of the cell’s growth cycle. If not, the cell will probably die. There is some chance that the cell will survive and behave differently because of the damaged DNA.  
Radiation Damage to DNA
Radiation-induced structural changes to DNA can be readily observed (Figure 2-2).
Figure 2.2: Radiation-Induced DNA Damage
Photomicrograph showing examples of radiation-induced chromosome damage in cancer cells following radiotherapy treatment (Bushong 1980). Courtesy of Scott Sorenson.

When DNA is damaged, the harm can be magnified by the cellular machinery.  One example of a possible consequence is a cell which loses control over replication-this mutation is better known as cancer. Ionizing radiation is thought to initiate (start), but not promote (help grow) mutations.
Types of Radiation Effects
Acute Effects: Short term effects
Very large radiation exposures can kill humans.  The lethal dose(LD) for half the population (50%) within 60 days is termed the LD_50/60d.  The LD_50/60d in humans from acute, whole body radiation exposure is approximately 400 to 500 rads (4-5 Gy). The temperature elevation in tissue caused by the energy imparted is much less than 1° C. The severe biological response is due to ionizing nature of X-ray radiation, causing the removal of electrons, and therby chemical changes in molecular structures. 
Deterministic Radiation Effects

A number of ionizing radiation effects occur at high doses. These all seem to appear only above a threshold dose. While the threshold may vary from one person to another, these effects can be eliminated by keeping doses below 100 rad. The severity of these effects increases with increasing dose above the threshold. These so-called deterministic (non-stochastic) effects are usually divided into tissue-specific local changes and whole body effects, which lead to acute radiation syndrome (Table 2-

Acute Whole Body Radiation Effects
Table 2-1: Acute Radiation Syndrome Sorenson, 2000

Syndrome	Symptoms	Dose (rad)
Radiation sickness	Nausea, vomiting	> 100 rad
Hemopoietic	Significant disruption of ability to produce blood products)	> 250 rad
LD50/60d	Death in half the population	> 250 - 450 rad
GI	Failure of GI tract lining, loss of fluids, infections	> 500 rad
CNS	Brain death	> 2,000 rad

These whole body (to entire body) doses are very unlikely for patients and staff from fluoroscopy or any diagnostic radiology study.
Several factors, such as total dose, dose rate, fractionation scheme, volume of irradiated tissue and radiation sensitivity all affect a given organ’s response to radiation. Radiation is more effective at causing damage when the dose is higher and delivered over a short period of time.  Fractionating the dose (i.e. spreading the dose out over time)  reduces the total damage since it allows the body time for repair.  Patient exposures are higher than attending staff but they occur over short periods of time whereas staff exposures are normally low and occur over several years.
Acute Localized Radiation Effects 
The Table 2-2 provides examples of possible radiation effects to skin caused by typical fluoroscopy exposures. Note that patient and technique factors can substantially increase exposure rates, significantly reducing the time necessary for the subsequent effect. 
Table 2-2: Dose and Time to Initiate Localized Radiation Effects

[Specific case studies of radiation-induced skin injury are presented in the next section]
Please note these localized effects will not be seen immediately (in the clinic).  These effects take time to develop and the minor effects may not be noticed and are often attributed to other causes.  This effectively results in a lack of warning for serious effects such as dermal necrosis. This lack of warning has led the FDA, HFH Radiation Safety Committee, and HFH Hospital Medical Executive Committee (HMEC) to have concerns about fluoroscopy utilization.  Consequently, fluoroscopy safety training and monitoring of fluoroscopy times were mandated.
Chronic Radiation Effects
Cataractogenesis
Cataract induction is of special interest to fluoroscopy operators since the lens of eye often receives the most significant levels of radiation (provided lead aprons are used). Radiation is known to induce cataracts in humans from single dose of 200 rad. Higher total exposures can be tolerated when accumulated over time. Personnel exposed to the maximum levels each year in the State of Michigan should accumulate no more than 150 rem to the lens of the eye over 30 years. As such, the risk for cataracts is likely to be small.  Nonetheless, it is imperative that individuals who approach the State of Michigan dose limit (1,250 mrem per quarter) wear leaded eyewear which can reduce the radiation dose to the eye by 85%.  Leaded eyewear will be provided, by Henry Ford Health System, to individuals with high eye doses. Once leaded eyewear is issued, this must be worn for all tableside X-ray procedures.
Stochastic (Probabilistic) Effects
Since the discovery of radiation by Roentgen, there have been many groups in which radiation effects have been studied (Bushong 1980) (Table 2-3): 
Table 2-3: Groups Studied for Radiation Effects Scott Sorenson, 2000.

Groups Studied for Health Effects

American Radiologists

Nuclear weapon survivors

Radiation-accident victims

Radiation-accident victims

Marshall Islanders (Atomic bomb fallout)

Residents with high levels of environmental radiation

Uranium miners

Radium watch-dial painters

Radioiodine patients

Ankylosing spondylitis patients (radiation therapy)

Thorotrast patients (radioactive contrast material)

Diagnostic irradiation in-utero

Cyclotron workers

Radiation Induced Cancer
These experiments have repeatedly shown that exposure to large radiation doses results in an elevated risk of cancer.  Thus, radiation is considered a known human carcinogen.  The experimental data suggest a non threshold dose response relationship (Figure 2-3).
Figure 2-3: Stochastic Radiation Effects Courtesy of Alan Jackson, 2001

Extrapolation of effects at higher doses using a straight line, predict that very small radiation doses have corresponding small risk of causing a cancer.  This straight line assumption, called the linear, no threshold, dose response relationship (LNT), involves the least amount of mathematical assumptions and is thereby consistent with the ancient principle of scientific philosophy known as Okam's razor (the simplest explanation which describes a phenomenon is the best). There are also some reasonable models which predict this relationship.  The slope of this straight line can be used as a risk coefficient to compare radiation risks with other hazards.
The LNT hypothesis implies that any amount of radiation exposure will increase an individual's risk of cancer.  Thus, all radiation doses should be mimimized or kept As Low As Reasonably Achievable (ALARA). 
Due to statistical considerations, such as the normal incidence of cancer (~30%), the ineffectiveness of the production of cancer by radiation,  stochastic effects can only be shown at doses much higher than that received by occupational workers.  The effects from lower radiation exposures (such as those encountered occupationally) are extrapolated from observations made at high doses (Upton 1999). In any case, this linear assumption is expected to provide the most conservative, or highest, risk estimates. The slope of the line is the risk coefficient. 
Radiation Risk
The cancer risk coefficient derived from the LNT model for radiation exposure is approximately 4.8 * 10^-4 per rem.  To put this number into perspective, imagine that you have two similar groups of 10,000 people; exposed and not exposed.  Each member of the exposed group receive 1 rem 1,000 mrem) of radiation exposure.  The control group does not recieve any additional radiation exposure beyond that received by natural sources.  Since the natural incidence of cancer is about 30%, the control group would expect about 3000 people to die from cancer. In comparison, the exposed group would expect that about 3005 people would die from cancer.  Thus, the exposed group should expect about 5 additional cancers from the 1 rem exposure.
One way better understand radiation risks is to compare radiation risks with other commonly accepted risks (Figures 2-4 and 2-5).
Figure 2-4: One in Million Risks Alan Jackson, 2001

Figure 2-5: One in Million Risks Alan Jackson, 2001

Radiation Induced Genetic Damage
Since radiation causes damage to DNA, genetic effects in human populations have long been suspected. Unrepaired or incorrectly repaired chromosonal damage can be passed on to subsequent generations. To date, there have been no studies which show an increase in genetic disorders in human populations. Nonetheless, animal studies have shown a relationship between radiation exposure and genetic defects which suggest a linear, no threshold, dose response relationship (LNT) much like that seen with cancer. 
The 7 million mice, "Megamouse" project revealed the following conclusions (Lam 1992):

• Different mutations differ significantly in the rate at which they are produced by a given dose. 
• There is a substantial dose rate effect with no threshold for mutation production.
•  The male was more radiosensitive than the female. The males carried most of the radiation induced genetic burden. 
• The genetic consequences of a radiation dose can be greatly reduced by extending the time interval between irradiation and conception. Six months to a year is
  recommended. 
• The amount of radiation required to double the natural and spontaneous mutation rate is between 20 to 200 rads. 

Radiation apparently does not cause unique types of mutations, but simply increases the mutations rate above their natural rate of occurrence. Controlled studies of genetic effects are only available from animal models. The risk coefficient for serious genetic disorders from radiation exposure is approximately 8 * 10^-5 per rem (NCRP 116).  This is less than the cancer risk coefficient (4.8 * 10^-4 per rem). Thus, if you protect against cancer, you are simultaneously protecting against genetic effects.  
Radiation Induced Premature Aging
In animal populations, radiation was correlated with premature aging .
In-utero Radiation Health Effects
Once conception has occurred (mother is pregnant), the unborn child (fetus) can be harmed by radiation.  Certainly, the unborn child can have the same health problems that an adult might have such as cancer and genetic defects.  The Law of Bergonie and Tribondeau predicts that a fetus would be exquisitely sensitive to radiation since they are:
1. Rapidly dividing;
2. Undifferentiated; and
3. Have a long mitotic future.
Studies of children exposed to x-rays in-utero support that prediction.  Thus, based on a concern for cancer induction, X-ray examination of pregnant patients has transformed from a standard health screening study to an extremely rare study.  Nonetheless, some X-rays of pregnant patients, particularly those to protect the life of the mother, are performed when necessary to protect the life of the mother typically under the guidance of a Radiologist.
In addition to the health effects which are a concern for an adult, there is also a serious concern about the possibility of developmental errors (teratogenesis) which can occur.  There are three general prenatal effects which have been observed:

1. Lethality; 
2. Congenital abnormalities at birth; and
3. Delayed effects, not visible at birth, but manifested later in life. 

The expression of effects are dependent upon the dose and stage of fetal development (Figure 2-6):
Figure 2-6: Fetal Developmental Radiation Risks
Courtesy of Scott Sorenson, 2000