MODULE II: RADIATION PROTECTION AND SAFETY

 

RADIATION PROTECTION & SAFETY

LEARNING OBJECTIVES:

At the end of  this module, the staff will be able to:

👉describe the principles of radiation exposure

👉list down the sources of radiation exposure

👉explain the uses of radiation monitoring devices

Radiation safety is vital for staff, visitors, and patients. The radiation protection is guided by the concept of keeping radiation exposure As Low As Reasonably Achievable (ALARA). The ALARA concept is based on the assumption that any radiation dose, no matter how small, can have some

adverse effect. 

All staff working in areas with potential radiation exposure should be aware of:

• How radiation exposure can occur
• Department policy on radiation safety
• Negative effects of radiation exposure, that radiation has a cumulative lifetime exposure
• Radiation safety officers and their role
• The principles of ALARA.

There are additional radiation safety precautions that need to be followed for patients who received permanent brachytherapy seed implants.

 

PRINCIPLES OF ALARA:

 The three major principles to assist with maintaining doses “As Low As Reasonably Achievable” are time, distance, and shielding.

Time:

Reducing the time of exposure can directly reduce radiation dose. The dose rate is the total amount of radiation absorbed relative to its biological effect. The dose rate is the rate at which the radiation is absorbed. Limiting the time of radiation exposure will reduce the radiation dose.

Examples of strategies to minimize time include the following:

💎Provide necessary patient education before the procedure

💎Teach, observe, and document the patient's ability to perform self-care measures before the procedure.

💎Evaluate the patient's understanding of the procedure, and discuss the reasoning for limiting the staff and family exposure.

💎 Provide the maximum amount of direct nursing care before the radioactive source is placed or administered.

💎Assemble all necessary equipment and supplies in the patient's room before the procedure to avoid unnecessary trips and ensure that equipment in the patient's room works properly before the radioactive source is administered.

💎Check frequently on the patient via intercom or telephone, anticipate the patient's needs, and encourage the patient to communicate any problems or concerns to the staff via intercom or telephone.

💎Use time efficiently when in contact with the patient and organize care. Nurses caring for patients with specific radioactive procedures may want to practice routine care activities.

💎 Rotate the nursing and ancillary staff caring for the patient receiving radioactive implants, and reassure the family that care is a priority and the patient will not be neglected.

Distance:

Increasing the distance between the body and the radiation source will reduce exposure by the square of the distance. Doubling the distance between the body and the radiation source will divide the radiation exposure by a factor of 4.

 

💿 With direct patient contact, stand as far away from the sealed radioactive source as possible, and stand at the head of the bed to take vital signs when in the room with a patient who has a gynecologic implant. Talk to the patient from the doorway rather than inside the room.

💿Assist the patient with needed tasks (e.g. unwrapping food items) from a distance.

💿Reinforce teaching of self-care activities while standing at a distance from the patient.   

Shielding:

Lead or lead equivalent shielding for X-rays and gamma rays is an effective way to reduce radiation exposure. There are various types of shielding used in the reduction of radiation exposure including lead aprons, mobile lead shields, lead glasses, and lead barriers. When working in radiation areas it is important to use shielding whenever possible.

📏Keep the shielding between the source and the person exposed. Build shields into the walls and floors of designated treatment rooms that are used for radioactive procedures that use high-energy gamma sources.

📏Continue to use principles of time and distance, even with shields, to further reduce radiation exposure.

📏Consider that maneuvering the shield may require increased nursing time in the room, making some use of shields unwarranted.

📏Select the correct material for shielding based on the type of emitters.

📏 Use more shielding in institutions that perform large gamma-emitting radioactive procedures.

SOURCES OF RADIATION  EXPOSURE

Natural sources of radiation:

We live in a radioactive world. Many natural sources of radiation have been present since the earth was formed. The three major sources of naturally occurring radiation are:

• Cosmic radiation

• Terrestrial radiation is known as sources in the earth's crust

• Internal sources or sources found in the human body

Most common sources from medical facilities:

🎀X-Ray producing equipment, usually found in the radiology department, and in surgery, emergency, and patient care areas, as well as in specialized areas such as the cardiac catheterization lab.

🎀Diagnostic radionuclides, usually found in the nuclear medicine department and in patient care areas.

🎀Therapeutic radionuclides, are usually found in the nuclear medicine department, and in patient care areas where therapeutic nuclear medicine patients are admitted.

🎀Brachytherapy sources, usually found in the same areas as therapeutic radionuclides.

🎀 Radiation therapy equipment, usually found in the radiation therapy department.

X-Ray: 

X-Rays are produced by several types of equipment. The types of X-ray equipment that you encounter depend on your specialty. In general, though, nurses most often see mobile radiographic and C-arm fluoroscopy units

Diagnostic radionuclides:

Diagnostic radionuclides are radioactive materials used in nuclear medicine departments. They include technetium-99m, gallium-67, thallium-201, and others. Overall, the risk presented by diagnostic radionuclides is minimal.

Therapeutic Radionuclides:

Therapeutic radionuclides are unsealed radioactive

materials administered in therapeutic doses to patients orally or by injection. They include:

• Radioiodine (I-131), usually administered orally to treat hyperthyroidism and thyroid cancer.
• Radio-phosphorus (P-32), which is administered by injection to treat certain types of cancer.

Therapeutic radionuclides present potential radiation hazards. But if proper safety practices are followed carefully, the risk here is also minimal.

Brachytherapy Sources:

Brachytherapy procedures use sealed sources containing radioactive material in therapeutic quantities to treat certain types of cancer. These sources are inserted into patients’ bodies, in areas such as the uterus, breast, and nasopharynx. The most commonly used radioactive materials include:

• Radioactive cesium (Cs-137).

• Radioactive iridium (Ir-192).

• Radioactive iodine (I-125).

Although brachytherapy sources containing radioactive materials are sealed, they do present potential radiation hazards. Here again, the risks are greatly reduced by following sound safety practices. 

Radiation Therapy Equipment:

Radiation therapy equipment uses ionizing radiation to treat certain forms of cancer and other abnormal tissues. This equipment focuses high-energy radiation from outside the body, on carefully selected tissues. It is usually administered in therapeutic doses. The linear accelerator and cobalt (Co-60) teletherapy units are examples of radiation therapy equipment.

RADIATION HAZARDS:

The potential hazard from radiation is exposure to ionizing rays or particles. Radiation exposure can occur in three types of situations:

✏When you are near an x-ray machine that is actually making an exposure. In this situation, x-rays scatter and can expose an unshielded body.

✏When you are near or in contact with a patient undergoing brachytherapy or radionuclide therapy. In this situation, radiation is emitted from the patient’s body, and/or from objects that have been contaminated by radioactive

material.

✏When you or your clothing have been contaminated by radioactive material.

Radioactive Contamination:

Potential radiation hazards are evident because they are associated with specific areas, equipment, and procedures. But radioactive contamination is not. By definition, radioactive contamination is the presence of radioactive materials anywhere they don’t belong — that is, anywhere

they are not appropriately identified, contained, and controlled.

Contamination is especially hazardous because it can be present without knowing, contamination may be external or it may be internal, due to ingestion, inhalation, or absorption of radioactive material. This can happen with radionuclide therapy, but is unlikely in brachytherapy sources are not likely to leak or break. Radioactive contamination can produce significant levels of localized radiation exposure.

RADIATION SAFETY PRECAUTIONS:

To minimize exposure:

💮Recognize radiation sources.

💮Reduce exposure time.

💮Increase distance from radiation.

💮Shield from radiation.

💮Avoid radioactive contamination.

Recognize Radiation Sources:

Radiation sources are marked by the international radiation hazard symbol: a purple trefoil on a bright yellow background.

• Be sure about the source of the hazard
• Only authorized personnel are to be posted in the area.
• Take appropriate precautions to reduce exposure and avoid contamination.
• Do not handle material labeled as radioactive unless trained and authorized to do so.

Reduce exposure time:

The key to reducing exposure time is planning. Make sure in advance that a radiotherapy nurse has everything needed to complete the necessary procedures near a radiation source as quickly as possible. 

Increase distance from the radiation:

Radiation levels vary inversely with the square of the distance from their source — levels decrease sharply with distance. The farther away place, the less radiation you are exposed to.

Shield from radiation:

Shielding will also reduce the level of radiation. Shielding is very effective with X-rays. Wear a lead apron, where provided. If hands are in the X-ray beam, wear lead gloves unless doing so would compromise patient care. Use lead shields when available.

A lead apron is ineffective in diagnostic nuclear medicine and radionuclide therapy. An appropriate bedside shield is effective in some situations (such as brachytherapy) and should be used wherever provided.

Avoid Radioactive Contamination:

⏰ Wear gloves, a gown, and a shoe cover if indicated.

⏰Avoid contact with objects or areas that may be contaminated.

⏰Don't eat, drink or smoke in areas where radioactive materials are in use.

⏰  Wash your hands when leaving the area

⏰ Read and follow all signs and instructions.

RADIATION MONITORING DEVICES:

RADIATION  DOSIMETERS:

A radiation dosimeter is a device, instrument or system that measures or evaluates, either directly or indirectly, the quantities exposure, absorbed dose or equivalent dose, or their time derivatives (rates), or related quantities of ionizing radiation. A dosimeter along with its reader is referred to as a dosimetry system.

Measurement of a dosimetry quantity is the process of finding the value of the quantity experimentally using dosimetry systems. The result of a measurement is the value of a dosimetry quantity expressed as the product of

a numerical value and an appropriate unit.

PROPERTIES OF DOSIMETERS:

 

In radiotherapy dosimetry the uncertainty associated with the measurement is often expressed in terms of accuracy and precision. 

The precision of dosimetry measurements specifies the reproducibility of the measurements under similar conditions and can be estimated from the data obtained in repeated measurements. High precision is associated with a small standard deviation of the distribution of the measurement results.

The accuracy of dosimetry measurements is the proximity of their expectation value to the ‘true value’ of the measured quantity. Results of measurements cannot be absolutely accurate and the inaccuracy of a measurement result is characterized as ‘uncertainty’.

The uncertainty is a parameter that describes the dispersion of the measured values of a quantity; it is evaluated by statistical methods (type A) or by other methods (type B), has no known sign and is usually assumed to be symmetrical. The error of measurement is the difference between the measured value of a quantity and the true value of that quantity. 

Radiation survey meters are required in most labs working with radiation. There are several types of survey meters, and care must be taken to select one sensitive to the radiation in use. Radiation exposure to humans can be broadly classified as internal and external exposures. In radiation therapy sealed sources are used almost exclusively and they are unlikely to cause internal exposure.

External exposure monitoring refers to measuring:  

⏳Radiation levels in and around work areas;

⏳Levels around radiation therapy equipment or source containers;

⏳Dose equivalents received by individuals working with radiation. 

Radiation monitoring is carried out:  

📕To assess workplace conditions and individual exposures; 

📕   To ensure acceptably safe and satisfactory radiological conditions in the workplace;

📕 To keep records of monitoring, over a long period, for the purposes of regulation or as good practice.

Radiation monitoring instruments are used both for area monitoring and for individual monitoring. The instruments used for measuring radiation levels are referred to as area survey meters (or area monitors) and the instruments used for recording the dose equivalents received by individuals working with radiation are referred to as personal dosimeters (or individual dosimeters). All instruments must be calibrated in terms of appropriate quantities used in radiation protection.  

AREA SURVEY METERS:

Radiation instruments used as survey monitors are either gas-filled detectors or solid-state detectors. The gas-filled detector is usually cylindrical in shape, with an outer wall and a central electrode well insulated from each other. The wall is usually made of tissue-equivalent material for ionization chamber detectors and of brass or copper for other types of detectors.

 

🎀 Survey meters come in different shapes and sizes depending on the specific application.

🎀 The gas is usually a non-electronegative gas in order to avoid negative ion formation by electron attachment that would increase the collection time in the detector, thus limiting the dose rate that can be monitored. The increase in charge collection time results from the relatively slow mobility of ions which is about three orders of magnitude smaller than that of electrons. Noble gases are generally used in these detectors. 

🎀 Beta-gamma survey meters have a thin end-window to register weakly penetrating radiation. 

🎀Depending upon the electronics used, the detectors can operate in a ‘pulse’ mode or in the ‘mean level’ or current mode. The proportional and GM counters are normally operated in the pulse mode.

🎀Because of the finite resolving time (the time required by the detector to regain its normal state after registering a pulse) these detectors will saturate at high-intensity

radiation fields. Ionization chambers, operating in the current mode, are more suitable for higher dose rate measurements.

Area survey meters commonly used for radiation protection level measurements: ionization chambers, a proportional counter, GM counters.  

Ionization chambers: 

⛳In the ionization region, the number of primary ions of either sign collected is proportional to the energy deposited by the charged particle tracks in the detector

volume. 

⛳Because of the linear energy transfer (LET) differences, the particle discrimination function can be used.

⛳Build-up caps are required to improve detection efficiency when measuring high-energy photon radiation, and they should be removed when measuring lower-energy photons (10 - 100 keV) and beta particles. 

Proportional counter:

🎀In the proportional region there is an amplification of the primary ion signal due to ionization by collision between ions and gas molecules (charge multiplication). This occurs when, between successive collisions, the primary ions gain sufficient energy in the neighbourhood of the thin central electrode to cause further ionization in the detector. The amplification is about 103 –104 -fold.

🎀Proportional counters are more sensitive than ionization chambers and are suitable for measurements in low-intensity radiation fields. The amount of charge collected from each interaction is proportional to the amount of energy deposited in the gas of the counter by the interaction.

Neutron area survey meters:

Neutron area survey meters operate in a proportional region, so the photon background can be easily discriminated against.

📏Thermal neutron detectors usually have a coating of a boron compound on the inside of the wall, or the counter is filled with BF3 gas.

📏A thermal neutron interacts with a 10B nucleus causing a reaction, and the particles can easily be detected by their ionizing interactions.

📏To detect fast neutrons the same counter is surrounded by a moderator made of hydrogenous material. The fast neutrons interacting with the moderator are thermalized and are subsequently detected by a BF3 counter placed inside the moderator.

Geiger–Muller counters:

 In GM multiplication spreads along the entire length of the anode. Gas-filled detectors cannot be operated at voltages beyond the GM region because they continuously discharge.

GM counters exhibit strong energy dependence at low photon energies and are not suitable for use in pulsed radiation fields. They are considered indicators of radiation, whereas ionization chambers are used for more precise measurements.GM detectors suffer from very long dead times, ranging from tens to hundreds of milliseconds.

A portable GM survey meter may become paralyzed in a

very high radiation field and yield a zero reading. Ionization chambers should therefore be used in areas where radiation rates are high.

 Semiconductor detectors:

Bulk conductivity detectors are formed from intrinsic semiconductors of very high bulk resistivity They act like solid-state ionization chambers on exposure to radiation and, like scintillation detectors, belong to the class of solid-state detectors.

extrinsic (i.e. doped with trace quantities of impurities such as phosphorus or lithium) semiconductors such as silicon or germanium are used to form junction detectors. They too act as solid-state ionization chambers on application of a reverse bias to the detectors and on exposure to radiation. The sensitivity of solid-state detectors is about 104 times higher than that of gas-filled detectors, owing to the lower average energy required to produce an ion pair in solid detector materials compared with air (typically one order of magnitude lower) and the higher density of the solid detector materials compared with air (typically three orders of magnitude higher). These properties facilitate the miniaturization of solid-state radiation monitoring instruments.

Commonly available features of area survey meters:

 📌A ‘low battery’ visual indication.

 📌Automatic zeroing, automatic ranging, and automatic back-illumination facilities.

 📌A variable response time and memory to store the data.  

📌The option of both ‘rate’ and ‘integrate’ modes of operation. 

📌An analog or digital display, marked in conventional  ‘ambient dose equivalent’ or ‘personal dose equivalent’ units. 

📌An audio indication of radiation levels.

📌Resettable/non-resettable alarm facility with adjustable alarm levels.

📌A visual indication of radiation with flashing LEDs. 📌 Remote operation and display of readings.

HANDHELD DOSIMETERS:

Handheld radiation survey meters are portable instruments that measure the activity or the exposure rate from radioactive material. Responders use these devices where radioactivity is suspected to be present in order to locate or assess the intensity of the radioactivity.

Handheld survey meters are used to take radiation readings on people and surrounding environments. These dosimeters are typically used to detect radiation in nuclear facilities and radiological facilities to ensure compliance with industry standards.

G-M tube detectors, ion chambers—like G-M tubes, ion chambers are gas filled radiation detectors—and scintillators are used in handheld survey meters to detect radiation. These dosimeters require training to operate.

PERSONAL DOSIMETER:

A personal dosimeter is worn by an individual over a specified period of time. The dosimeter is usually sent to a facility that examines the radiation dose, but they can also be read at the site of a hot zone. These dosimeters are very accurate.

There are four types of personal dosimeters:

Film badges: The most common type of radiation dosimeter, use film and filters to detect radiation dose levels. They are not reusable but give a permanent record of exposure.

Optically stimulated luminescence (OSL) dosimeters: Use aluminum oxide to detect radiation dose levels. These dosimeters are ideal for pregnant women because of their increased sensitivity.

Thermoluminescent dosimeters (TLDs): Use a lithium fluoride (LiF) or a CaD₂ crystal to detect radiation levels. These dosimeters measure radiation by a light that the crystal produces when it’s heated by radiation.

Direct-ion storage (DIS) dosimeters: are electronic dosimeters that attach to a breast pocket. DIS dosimeters use ion chambers and an electronic element to detect radiation dose levels, however they are not equipped with an alarm. DIS dosimeters can operate at high radiation doses.

PERSONAL EMERGENCY RADIATION DETECTORS (PERDS) :

Personal emergency radiation detectors (PERDs) are used in hazardous environments with high dose rates of radiation. These dosimeters are typically used in emergency response applications because they can be used in cold zones, warm zones, and hot radiation zones.

PERDs are worn on the body and detect photons. If the radiation dose exceeds the preset range, an alarm will sound, alerting the individual to harmful exposure rates or an accumulated dose that exceeds radiation exposure standards.

POCKET IONIZATION CHAMBER:

Pocket ionization chambers are simple devices, no larger than a pen, that can be read in real time. These dosimeters are battery operated, so they need to be charged before and after use.

Common names for this type of dosimeter include: self-reading pocket dosimeter, self-indicating pocket dosimeter, and quartz-fiber dosimeter. Pocket ionization chambers do not record cumulative doses of radiation and do not alarm. This type of dosimeter is less accurate than more modernized types of dosimeters.

SPECIAL CONSIDERATIONS:

⏰Radiation therapy staff should understand the documented procedures for the operation of the equipment with which they work, including the safety features, and should be trained, with periodic refresher training, in what to do if things go wrong. Additional education and training should be conducted when new devices or techniques are introduced into radiation therapy practice.

⏰For external beam radiotherapy, HDR and PDR brachytherapy, no one should be in the treatment room during the delivery of treatment, except the patient being treated. All attending personnel should be in appropriately shielded areas.

⏰Safety features such as interlocks, the presence of accessories and the functionality of survey meters should be checked daily prior to patient treatment.

⏰Sealed sources should be subject to leak tests prior to their first use and at regular intervals thereafter, in conformity with international standards.

⏰Area surveys should be performed periodically  around all treatment units and check sources, units, shielded safes and source storage facilities.

Specific local rules and procedures for external beam radiotherapy:

The safe operation of external beam radiotherapy units requires procedures for area surveys, interlock checks, leak tests (for sealed sources) and procedures for contingencies such as a source becoming stuck in the on position or partially in the on position. Such procedures require that the necessary equipment be available, calibrated and in working order, including:

 ✔ A radiation monitor;

 ✔ Leak test capabilities (for radioactive sources);

✔ Personal alarm dosimeters, especially for unplanned  exposures.

➖The procedures for the use of radiation monitoring equipment should take into account that some instruments can give erroneous readings in a high radiation field, and that this phenomenon, if it occurs, can be addressed by starting the monitoring from outside the room in which the source is located.

➖The presence of other staff in the area of the control panel should be kept to the minimum  

➖Irradiation that involves the extended use of high energy X rays, such as beam calibration, dosimetry and quality control measurements, should be scheduled to take place at the end of the day’s clinical roster so that neutron activated radionuclides  can decay significantly overnight.

Specific local rules and procedures for brachytherapy:

➖An inventory of sources should be maintained, giving the radionuclide, location and activity with reference date of each source at the facility as well as its serial or batch number, and a unique identifier. The unique identifier may be either a color coded identifier or an alphanumeric identifier.

➖Sources should never be left on preparation surfaces. They should be either in storage, in transit or in use.

➖Regular leak tests should be performed for sealed sources,

➖Area surveys should be performed periodically around the source storage facilities.

➖The source storage facilities should be marked to indicate that they contain radioactive materials, and instructions should be provided on how to contact the RPO, medical physicist or other responsible radiation safety individual in the event of an emergency.

➖Source storage rooms should be kept locked at all times, except when access is required to remove or return a source.

➖After every brachytherapy treatment, all brachytherapy sources should be removed from the patient, except in the case of permanent implants. 

➖The patient should be monitored with a radiation survey meter to ensure that no radioactive source remains in or on the patient. 

➖Bed linen, dressings, clothing, waste, and equipment should be kept within the room where the removal of sources takes place until all sources are accounted for, and should be monitored with a radiation detector. 

➖Mobile containers and portable equipment containing radioactive sources should be removed to storage or to a secure place when not in use.

➖Sterilization processes in brachytherapy should be appropriate and should be consistent with the manufacturer’s recommendations to prevent damage to sources and applicators that could affect safety.

REFERENCES:

1. https://wwwpub.iaea.org/MTCD/publications/PDF/PUB1775_web.pdf
2. https://www.flyability.com/dosimeter