Facility Safety Management in Radiation Therapy
Introduction
For more than a century, radiation has been used safely to treat cancer patients. The potential dangers of ionizing radiation were recognized early on, leading to procedures that minimize worker and public exposure to radiation.
It’s quite important for technologists to be familiar with radiation safety principles as they pertain to their practice and to have knowledge of their facility safety management.
In this article we will walk you through the signage and labelling, the radiation treatment room requirement, the equipment and area monitoring and the personnel monitoring.
Signage and labelling requirements
There are two sorts of zones that surround a treatment room in radiation therapy facility:
- The Radiation Safety Officer RSO does not supervise the exposure of people in an uncontrolled area. For an uncontrolled area, the dosage equivalent limit is 0.02 mSv/week
- The RSO supervises the exposure of individuals in a controlled area. A regulated area’s dosage equivalent limit is 0.1 mSv/week. Badges are required for anyone entering a restricted area
- Any area where radiation is emitted, such as radiation treatment rooms, must have a sign showing the level of radiation present. The signs for these radiation zones are usually labeled as in Table 1 and Fig 2
These symbols are usually printed in purple, magenta, or black over a yellow background.
Radiation treatment room requirement
Because occupational exposure from the accelerator to the radiation therapist and the general public must not exceed the maximum permitted dose (MPD) which is 50 mSv for radiation worker and 5 mSv for general public as noted in the table 4, modern high-energy linear accelerators are housed in strongly shielded vaults with up to 6-10 feet of concrete (figure 3).
NCRP Reports describe the guidelines for designing treatment room shielding.
However, the following is a quick summary of the main criteria for such shielding and other technical needs for designing a treatment room.
These factors should be included in the design of the treatment room:
- The primary radiation shielding is the barrier that is sufficient to reduce primary radiation to the required level of attenuation
Primary radiation is the radiation that leaves the linear accelerator’s collimation system and is utilized to treat patients. Because of the tremendous intensity of the primary beam, primary shielding is generally the thickest.
- Secondary radiation shielding is a barrier that is effective enough to reduce secondary radiation to the appropriate level
Secondary radiation includes leakage and scatter radiation. Any radiation that escapes from the treatment equipment that is not part of the primary beam is referred to as leakage radiation. It has the same amount of energy as primary radiation.
Scatter radiation, on the other hand, is lower-energy radiation that is scattered in all directions from the machine and from the patient.
- When a photon beam with an energy more than 10 MV is generated, the beam becomes contaminated by neutrons produced as a result of the photodisintegration process that happens in the target and collimators
At 15 MV, neutrons become a significant issue in shielding calculations. when performing primary and secondary shielding calculations, many factors must be taken into account such as workload(W), use factor (U), occupancy factor (T), distance (d), dose equivalent limit (P)…
Aside from appropriate shielding for the treatment room, a range of other safety procedures are implemented to protect the treating radiation therapist and the general public:
- Radiation warning signs to indicate radiation areas
- Warning lights that illuminate when the radiation beam is on
- Radiation warning signs to indicate radiation areas
- Door interlocks to turn the treatment machine off if the treatment room door is open during the treatment
- Constant visual and audio contact with the patient in the treatment room during treatment via a closed-circuit camera and speaker
- Multiple emergencies shut-off buttons located at several locations within and outside the treatment room
These safety measures are normally governed by state rules, which differ from state to state.
Equipment and area monitoring
The instruments used for measuring radiation levels are referred to as area survey meters. Their purpose is to measure:
- Radiation levels in and around work areas
- Radiation levels around radiotherapy equipment or source containers
The most basic radiation detection instrument is a gas-filled detector. In a radiation therapy department, we can find:
- Ionization chamber (“cutie-pie”): Ionization chambers are used to measure radiation doses in low-level areas. For good sensitivity, they have huge volumes. These meters are ideal for quantitative radiation measurements, such as routine area surveys and patient surveys
- GM counters: GM counters are far more sensitive than survey meters in the ionization chamber. They are the ideal choice for qualitative radiation protection assessments such as locating lost sources, discovering holes in shielding, and contamination surveys, but they are not a good choice for quantitative radiation measurements due to their high energy dependence and long dead times
- Neutron detectors: Neutron detectors are similar to GM counters, but the tubes contain boron trifluoride (BF3) gas. Because neutrons cannot directly ionize a gas, neutron detection is accomplished by transforming neutrons into alpha particles, which can then ionize the gas in proportion to the neutron dose absorbed by the neutron detector
As a matter of fact, 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 of time, for the purposes of regulation or good practice
Personnel monitoring
The instruments used for recording the equivalent doses received by individuals working with radiation are referred to as personal dosimeters or individual dosimeters.
Personnel monitoring for professionally exposed people must be employed in regulated areas. NCRP Report No. 33 recommend that individuals receiving a dose of more than 25% of MPD should get personnel monitoring. For persons that receive a dose above 10% of MPD, the NRC requires a personnel monitoring as well.
For that reason, individuals who regularly work in controlled areas or those who work full time in supervised areas should wear personal dosimeters to have their doses monitored on a regular basis.
Radiation Dosimetry is in fact the systematic measurement of the absorbed dose in matter and tissue resulting from exposure to ionizing radiation. Actually, the radiation dosimetry badge does not provide protection, but rather detects and measures the amount of ionizing radiation to which personnel have been exposed.
The majority of people keep their radiation dosimetry badge fastened to their lapel on their chest. This is to keep track of the “whole body dose.” If a woman is pregnant, she should wear an extra badge on her abdomen. Employees should wear their badges at all times during the day. The dosimeter should not be taken home or exposed to extremely hot or humid conditions and obviously should only be worn by the person whose name appears on the label.
They are exchanged on monthly or quarterly basis. And the person responsible for collecting the badges is usually from the dosimetry department and he/she will be the one directing it to the radiation safety office and giving back the exposure evaluation afterwards.
There are many types of personal dosimeters, the most used ones are:
- Thermoluminescent dosimeter (TLD) badge: TLDs are used for badges on the body and on the ring. TLDs that have been irradiated capture electrons that, when heated, generate visible light. The amount of visible light received by the TLD is proportional to the amount of radiation received.
- Film badge: Films are frequently used as dosimeters for body badges. The optical density of the irradiated film is proportional to the radiation dosage received by the film and serves as a measure of the radiation dose received by the individual wearing the film badge. It’s worth noting that TLDs and film badges may contain two separate TLDs or films and that a filter may be placed over one set to indicate the penetrating ability of the radiation that traveled through it
- Electronic dosimeter: Electronic dosimeters have lately gained popularity because, unlike TLD or film dosimeters, they can quantitatively monitor radiation exposure in real time and produce a readout instantaneously
- Individual dosimeters are also used to verify the effectiveness of radiation control practices in the workplace. It is useful for detecting changes in radiation levels in the workplace and to provide information in the event of accidental exposures
Conclusion
The purpose of any radiation safety program is to keep patients, workers, and the general public safe. As low as reasonably achievable or in radiation term “ALARA” should always be the goal of a radiation safety program. Every reasonable effort must be made to keep radiation exposures in a radiation oncology department as close to the maximum allowed dose limits as possible.
References
- Hasan Murshed (editor) – Fundamentals of Radiation Oncology_ Physical, Biological, and Clinical Aspects-Academic Press (2019)- Chapter 2 Radiation Protection and Safety
- Radiation Badge Training – UCONN HEALTH
- Radiation Oncology Practice Standards Part B Guidelines V2.1
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