Chapter Three: Radiation protection ( Radiological protection)

1. Chapter Three: Radiation protection (Radiological protection) [ Minimize exposure (human exposure) to radiation ] Assistant Prof. Dr. Asaad H. Ismail PhD Medical Physics Salahaddin University-Erbil E-mail: asaad.ismail@su.edu.krd

2. Radiation protection Principle of radiation protection Definition: International Atomic Energy Agency (IAEA) is defined radiation protection as "The protection of people from harmful effects of exposure to ionizing radiation, and the means for achieving this“ - Exposure can be from a radiation source external to the human body or (internal) due to an intake of radioactive material into the body. • International commission of radiation protection (ICRP) suggested general principles of radiation protection as three key words; • Justification • Optimization • Dose limit.

3. Two principles are source-related and apply in all exposure situations The principle of justification: Any decision changes the radiation exposure situation should do more good than harm. This means that, by introducing a new radiation source, by reducing existing exposure, or by reducing the risk of potential exposure, one should achieve sufficient individual or societal benefit to offset the detriment it causes. The principle of optimization of protection: the number of people exposed, and the magnitude of their individual doses should all be kept as low as reasonably achievable (ALARA), taking into account economic and societal factors. This means that the level of protection should be the best under the prevailing circumstances, maximizing the margin of benefit over harm. In order to avoid severely inequitable outcomes of this optimization procedure, there should be restrictions on the doses or risks to individuals from a particular source One principle is individual-related and applies in planned exposure situations. The principle of application of dose limits: The total dose to any individual from regulated sources in planned exposure situations other than medical exposure of patients should not exceed the appropriate limits recommended by the Commission. The concepts of dose constraint and reference level are used in conjunction with the optimization of protection to restrict individual doses. A level of individual dose, either as a dose constraint or a reference level, always needs to be defined. The initial intention would be to not exceed, or to remain at, these levels, and the ambition is to reduce all doses to levels that are as low as reasonably achievable, economic and societal factors being taken into account. Diagnostic reference levels are already being used in medical diagnosis (i.e., planned exposure situations) to indicate whether, in routine conditions, the levels of patient dose or administered activity from a specified imaging procedure are unusually high or low for that procedure. If so, a local review should be initiated to determine whether protection has been adequately optimized or whether corrective action is required.

4. Principles of radiation protection in medical fields from the ICRP Recommendation Unique characteristics of radiological protection in medicine Several features of radiation exposure in medicine for patients require an approach to radiological protection that is somewhat different from that for other types of radiation exposure. The exposure of patients is deliberate. Except in radiation therapy, it is not the aim to deliver radiation dose, but rather to use the radiation to provide diagnostic information or to conduct an interventional procedure. Medical uses of radiation for patients are voluntary in nature, combined with the expectation of direct individual health benefit to the patient. The voluntary decision is made with varying degrees of informed consent that includes not only the expected benefit but also the potential risks. The amount of information provided in order to obtain informed consent varies based on the exposure level and the possible emergent medical circumstances that may be attributable to radiation exposure. The exception to the concept of a voluntary exposure leading to a direct individual medical benefit is the use of radiation in biomedical research. In these circumstances, the voluntary exposure usually accrues to a societal benefit rather than an individual benefit. Informed consent is always needed. Screening is performed with the aim of identifying a disease process that has not become manifest clinically. Current screening practices using ionizing radiation appear to be valid and are recommended for certain populations. Patients undergoing screening should be fully informed of the potential benefits and risks, including the radiation risks. Each application of ionizing radiation for screening of asymptomatic individuals should be evaluated and justified with regard to its clinical merit.

5. Application of principles of radiation protection in medical fields (Regulation of dose uptake) Because medical exposure of patients has unique considerations, it addresses the proper (healthy) application of the fundamental principles (justification, optimization of protection and application of dose limits) of radiation protection. With regard to medical exposure of patients, it is not appropriate to apply dose limits, because such limits would often do more harm than good. Often, there are concurrent chronic, severe, or even life-threatening medical conditions that are more critical than the radiation exposure. The emphasis is then on justification of the medical procedures and on the optimization of radiological protection. In diagnostic and interventional procedures, justification of procedures (for a defined purpose and for an individual patient), and management of the patient dose commensurate with the medical task, are the appropriate mechanisms to avoid unnecessary or unproductive radiation exposure. Equipment features that facilitate patient dose management, and diagnostic reference levels derived at the appropriate national, regional, or local level, are likely to be the most effective approaches. In radiation therapy, the avoidance of accidents is a predominant issue. With regard to comforters and carers, and volunteers in biomedical research, dose constraints are appropriate.

6. 1) Justification Justification in radiological protection of patients is different from justification of other radiation applications, in that generally the very same person enjoys the benefits and suffers the risks associated with a procedure. (There may be other considerations: attendant occupational exposures could be correlated with patient doses or sometimes there can be a trade-off; screening programs may benefit the population rather than every screened person. But usually, risks and benefits accrue to the same person). And, a very important aspect in daily medical practice: the fact that a method or procedure can be regarded as justified as such does not necessarily mean that its application to the particular patient being considered is justified. There are three levels of justification of a radiological practice in medicine. ① At the first and most general level, the proper use of radiation in medicine is accepted as doing more good than harm to society. ② At the second level, a specified procedure with a specified objective is defined and justified. The aim of the second level of justification is to judge whether the radiological procedure will improve the diagnosis or treatment, or will provide necessary information about the exposed individuals. ③ At the third level, the application of the procedure to an individual patient should be justified. Hence all individual medical exposures should be justified in advance, taking into account the specific objectives of the exposure and the characteristics of the individual involved.

7. 2) Optimization Optimization of protection for patients is also unique. In optimization of protection of the patient in diagnostic procedures, again the same person gets the benefit and suffers the risk, and again individual restrictions on patient dose could be counterproductive to the medical purpose of the procedure. The optimization of radiological protection for patients in medicine is usually applied at two levels: 1) The design, appropriate selection, and construction of equipment and installations; 2) The day-to-day methods of working. The basic aim of this optimization of protection is to adjust the protection measures for a source of radiation in such a way that the net benefit is maximized. The optimization of protection in medical exposures does not necessarily mean the reduction of doses to the patient. The optimization of radiological protection means keeping the doses ‘as low as reasonably achievable, economic and societal factors being taken into account’, and is best described as management of the radiation dose to the patient to be commensurate with the medical purpose.

8. 3) Diagnostic reference levels The diagnostic reference level (DRL) applies to medical exposure, as a form of investigation level. DRLs are supplements to professional judgment and do not provide a dividing line between ‘good’ and ‘bad’ medicine. They contribute to good radiological practice in medicine. The numerical values of DRLs are advisory; however, implementation of the DRL concept may be required by an authorized body. It is inappropriate to use the numerical values for DRLs as regulatory limits or for commercial purposes. The values should be reviewed at intervals that represent a compromise between the necessary stability and the long-term changes in the observed dose distributions. The selected values could be specific to a country or region. A DRL can be used to improve a regional, national, or local distribution of observed results for a general medical imaging task, by reducing the frequency of unjustified high or low values. Also it promotes attainment of a narrower and optimal range of values that represent good practice for specific imaging protocols. The guiding principles for setting a DRL are: ① the regional, national, or local objective is clearly defined, including the degree of specification of clinical and technical conditions for the medical imaging task; ② the selected value of the DRL is based on relevant regional, national, or local data; ③ the quantity used for the DRL can be obtained in a practical way; ④ the quantity used for the DRL is a suitable measure of the relative change in patient tissue doses and, therefore, of the relative change in patient risk for the given medical imaging task; ⑤ the manner in which the DRL is to be applied in practice is clearly illustrated.

9. I. EXTERNAL RADIATION PROTECTION (Factors in external dose uptake) The three basic methods used to reduce the external radiation hazard are time, distance, and shielding. Good radiation protection practices require optimization of these fundamental techniques. A. Time The amount of radiation an individual accumulates will depend on how long the individual stays in the radiation field, because: Dose (mrem) = Dose Rate (mrem/hr) x Time (hr) Therefore, to limit a person’s dose, one can restrict the time spent in the area. How long a person can stay in an area without exceeding a prescribed limit is called the "stay time" and is calculated from the simple relationship:

21. II) INTERNAL RADIATION PROTECTION Internal radiation exposure results when the body is contaminated internally with a radionuclide. When radioactive materials enter into the body, they are metabolized and distributed to the tissues according to the chemical properties of the elements and compounds in which they are contained. For example, consider a complex molecule which can be equally satisfied with a C-12 (stable) atom or a C-14 (radioactive) atom at its regular carbon position. If the C-14 decays to nitrogen; the molecular structure is affected. If the molecule were DNA, this might be equivalent to gene mutation. Once radioactive material is in the body, little can be done to speed its removal. Thus, internal radiation protection is concerned with preventing or minimizing the deposition of radioactive substances in personnel. A. Radioactive Materials in the Body Radioactive substances, like other toxic agents, may gain entry into the body by four processes: 1. Inhalation - breathing radioactive aerosols or dust (Radon and thoron) 2. Ingestion - drinking contaminated water, or transferring radioactivity to the mouth 3. Absorption – entry through intact skin 4. Injection - puncture of skin with an object bearing radioactive materials

22. B. Guidelines The basic methods to control and prevent radioactive contamination which can lead to internal radiation exposures are: 1. Isolate the contamination at the source: seal samples, use a fume hood, use catch trays lined with paper, change gloves often to avoid cross contamination. 2. Restrict contaminated personnel and articles: separate your radioactive and non-radioactive work areas. 3. Establish and maintain the contamination control zone. 4. Follow established laboratory procedures. Proper protective clothing, designated work areas, surface contamination monitoring, personnel monitoring, etc. are required in all laboratories that use radioactive material. C. Limits Limits pertaining to internal emitters are set up for particular radionuclides. These limits are called Annual Limits on Intake (ALI’s). A permissible constant ALI of a radionuclide is a quantity (in µCi) which when present continuously in the body will deliver a dose rate not exceeding the maximum permissible dose rate. The constant ALI must not deliver a committed effective dose equivalent of more than 50 rem per year to any individual organ or tissue or more than 5 rem per year to the whole body. The concentrations of radionuclides in air required to yield an ALI are called Derived Air Concentrations (DAC’s). A DAC is the concentration of a radionuclide (in microcuries per milliliter) which, when taken into the body on an occupational exposure basis, results in an organ burden which produces the maximum permissible committed effective dose equivalent, e.g. one ALI to the organ of interest. Some of the factors which are considered in calculating ALI's and DAC's are: 1. the type and energy of the radiation emitted 2. its distribution in the body 3. the solubility of the compound containing the isotope 4. the effective half-life of the isotope

23. D. Internal Exposure Monitoring Internally deposited radioactive material can be monitored by measuring the radiation emitted from the body or by measuring the amount of radioactive material contained in the urine or feces. Such monitoring techniques are called bioassays. Bioassays are required whenever surveys or calculations indicate that an individual has been exposed to concentrations of radioactive material in excess of established limits BIOASSAY PROGRAM 1. Biological Samples Biological samples may be taken from all personnel working with heavy elements, millicurie quantities of tritium, or the training reactor, at intervals specified by the Radiation Control Officer. Biological samples will be taken from all personnel who have ingested or who are suspected to have ingested, radioactive material, including other occasions if deemed necessary. 2. Partial body/whole body counting Thyroid monitoring of individuals working with radioiodine is required as specified in the Application of Bioassay for I-125 and I-131 . 3. Participation All personnel working with tritium and radioiodine will receive a questionnaire each month regarding their use of these radionuclides. If the amount of activity used does not meet the participation criteria this fact should be noted on the questionnaire. The questionnaire serves to remind the individual of the program requirements and to verify participation of all individuals in the program.

24. III. General Precautions and Rules of Thumb General Precautions for Working with Radioactive Materials 1. Always keep radioactive and nonradioactive work separated as far as possible, preferably by maintaining rooms and/or areas used solely for radioactive work. 2. Always work over a spill tray and in a ventilated hood (except with compounds in a nonvolatile form). 3. Always use the minimum quantity of radioactivity compatible with the objectives of the experiment. 4. Always wear protective clothing, safety glasses and gloves when handling radioactivity. 5. Always wash your hands and monitor yourself before leaving a radioactive work area. 6. Always work carefully and monitor the working area regularly with both swipes and a survey meter to avoid ruining experiments by accidental contamination. 7. Always label containers of radioactive material clearly, indicating nuclide, total activity, compound, specific activity, date and the exposure rate at the surface of the container. 8. Never eat, drink, smoke or apply cosmetics in an area where unsealed radioactivity is handled. 9. Never use ordinary handkerchiefs; use paper tissues and dispose of them as radioactive waste as necessary. 10. Never work with cuts or breaks in the skin unprotected, particularly on the hands or forearms. 11. Never pipette radioactive solutions by mouth.

25. 12. In the event of a spill it is essential to minimize the spread of contamination: a) Cordon off the suspected area of contamination. b) Ascertain, if possible, the type of contamination, i.e. the nuclide(s) involved (it may be necessary to use breathing apparatus, protective clothing or other equipment). c) Determine the area of contamination by monitoring with a survey meter after taking the necessary precautions. d) Starting from the outer edge, decontaminate the area in convenient sectors by wiping or scrubbing, if necessary, as described in Chapter 6. e) Before moving on, ensure that a sector is clean by monitoring with swipes. 13. Dispose of all radioactive waste according to statutory requirements. Short-lived radionuclides, for example, 32P, may be stored with suitable shielding and left to decay. After 4 half-lives less than 10% of the original activity remains, after 7 half-lives <1%, and after 10 half-lives <0.1%. The rule of thumb is to store radioactive waste for 10 half-lives before disposal. For longer-lived radionuclides, for example, 3H, this is impracticable and alternative disposal arrangements must be made. 14. Film badges should be worn for all radioactive work except with the low energy, -emitting radionuclides 3H, 14C and 35S. 15. Federal and State regulations require that occupational exposure should not exceed 5 rem (50 mSv) per year to the whole body. The exposure of the general public should not exceed 100 mrem (1 mSv) per year to the whole body. 16. To minimize the dose to the extremities, tongs or other remote handling equipment should be used where appropriate.

26. Rules of Thumb (from NIH Publication 79-18. DHEW) Beta Particles 1. Beta particles of at least 70 keV energy are required to penetrate the nominal protective layer of the skin (7mg/cm- or 0.07mm). 2. The average energy of a beta-ray spectrum is approximately one-third the maximum energy. 3. The range of beta particles in air is ~ 12 ft/MeV. (Maximum range of 32P beta is 1.71 MeV x 12 ft/MeV ≃ 20 ft). 4. The dose rate in rads per hour in a solution by a beta emitter is 1.12 EC/ where E is the average beta energy per disintegration in MeV, C is the concentration in microcuries per cubic centimeter, and  is the density of the medium in grams per cubic centimeter. The dose rate at the surface of the solution is one-half the value given by this relation. (For 32P average energy of approximately 0.7 MeV, the dose rate from 1 µCi/cm3 (in water) is 1.48 rad/hr). 5. The surface dose rate through the nominal protective layer of skin (7 mg/cm2) from a uniform thin deposition of 1 µCi/cm2 is about 9 rad/hour for energies above about 0.5 MeV. Note that in a thin layer, the beta dose rate exceeds the gamma dose rate, for equal energies released, by about a factor of 100. 6. For a point source of beta radiation (neglecting self and air absorption) of activity in millicuries, the dose rate in rad/hr at 1 cm is approximately equal to 200 x activity, and varies only slowly with beta energy. Dose rate for 1 mCi 32 P at 1 cm is approximately 200 rad/hour.

27. Gamma Rays a. For a point source gamma emitter with energies between 0.07 and 4 MeV, the exposure rate (mR/hr) within approximately 20% at 1 foot = 6CEn, where C is the activity in millicuries; E, the energy in MeV; and n, the number of gammas per disintegration. b. The dose rate to tissue in rads/hr in an infinite medium uniformly contaminated by a gamma emitter is 2.12 EC/, where C is the number of microcuries per cubic centimeter, E is the average gamma energy per disintegration in MeV, and  is the density of the medium. At the surface of a large body, the dose rate is about half of this. X-Ray a. The exposure rate at 2 feet from diagnostic x-ray equipment operated at 100 kVp and 100 milliamperes is approximately 2.3 roentgen/second. b. Exposure rate at the fluoroscopy table with tube potential at 80 kVp and tube current of 1 milliampere should not exceed 2.1 roentgen/minute. c. Scattered radiation can be as penetrating as the primary beam. X-Ray Diffraction a. The x-ray beam intensities from the primary beam can be as much as 400,000 R/min. b. Scattered radiation 10 cm from the points of scatter about the x-ray tube head has been measured to be on the order of 150 R/hr. c. The threshold dose sufficient to produce skin erythema is 300 to 400 R. d. The minimum cataractogenic single dose is 200 rads, while a dose of 750 rads exhibits a high incidence of cataract formation. Miscellaneous a. The activity of any radionuclide is reduced to less that 0.1% after 10 half-lives. b. For material with a half-life greater than six days, the change in activity in 24 hours will be less than 10%.

28. IV. SPECIFIC HANDLING PRECAUTIONS FOR VARIOUS RADIONUCLIDES Radioiodination and Safety , as will as guidelines on handling precautions for the following commonly used radioisotopes are mentioned and listed in reference “RSSC RADIATION PROTECTION 07/11 ? : H-3 C-14 P-32 P-33 S-35 Cr-51 I-125

29. Categories of exposure International commission of radiation protection (ICRP) distinguishes between three categories of exposures 1) Occupational exposure Occupational exposure is defined as all radiation exposure of workers incurred as a result of their work. ICRP limits its use of ‘occupational exposures’ to radiation exposures incurred at work as a result of situations that can reasonably be regarded as being the responsibility of the operating management. The employer has the main responsibility for the protection of workers. 2) Public exposure Public exposure encompasses all exposures of the public other than occupational exposures and medical exposures of patients. It is incurred as a result of a range of radiation sources. The component of public exposure due to natural sources is by far the largest, but this provides no justification for reducing the attention paid to smaller, but more readily controllable, exposures to man-made sources. Exposures of the embryo and fetus of pregnant workers are considered and regulated as public exposures. 3) Medical exposure of patients Radiation exposures of patients occur in diagnostic, interventional, and therapeutic procedures. There are several features of radiological practices in medicine that require an approach that differs from the radiological protection in other planned exposure situations. The exposure is intentional and for the direct benefit of the patient. The application of these recommendations to the medical uses of radiation therefore requires separate guidance.

30. Status of Exposure (What is the radiation exposure situations ?) International Committee on Radiation Protection (ICRP) organized the exposure situation into the following types ; 1) Planned exposure – defined as "...where radiological protection can be planned in advance, before exposures occur, and where the magnitude and extent of the exposures can be reasonably predicted." These are such as in occupational exposure situations, where it is necessary for personnel to work in a known radiation environment. 2) Emergency exposure – defined as "...unexpected situations that may require urgent protective actions ". This would be such as an emergency nuclear event. 3) Existing exposure – defined as "...being those that already exist when a decision on control has to be taken". These can be such as from naturally occurring radioactive materials which exist in the environment.