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RADIATION PROTECTION IN NUCLEAR MEDICINE
PART 6. MEDICAL EXPOSURE
1.
RESPONSIBILITIES
With regard to responsibilities for medical exposure, registrants and licensees shall
ensure that (BSS II.1–3):
 no patient is administered a diagnostic medical exposure unless the exposure
is prescribed by a medical practitioner;
 medical practitioners are assigned the primary task and obligation of ensuring
overall patient protection and safety in the prescription of, and during the
delivery of, medical exposure;
 medical and paramedical personnel are available as needed, and are either
health professionals or have appropriate training to discharge their assigned
tasks in the conduct of the diagnostic or therapeutic procedure that the
medical practitioner prescribes;
 the exposure of individuals incurred knowingly while voluntarily helping (other
than in their occupation) in the care, support or comfort of patients undergoing
medical diagnosis or treatment is constrained as specified in Appendix C; and
 training criteria are specified or subject to approval, as appropriate, by the
Regulatory Authority in consultation with relevant professional bodies.
Licensees should ensure that for diagnostic uses of radiation, the imaging and
QA requirements are fulfilled with the advice of a qualified expert in nuclear medicine
physics.
The licensee shall ensure that workers (medical practitioner, medical physicist,
technologist):
 follow any applicable rules and procedures for the protection and safety of
patients, as established by the licensee;
 are competent in the operation and use of the equipment and sources
employed in nuclear medicine, of the equipment for radiation detection and
measurement, and of the safety systems and devices, commensurate with
the significance of the workers’ functions and responsibilities; and
 know their expected response in the case of patient emergencies.
2.
JUSTIFICATION
Medical exposures should be justified by weighing the diagnostic or therapeutic
benefits they produce against the radiation detriment they might cause, taking into
account the benefits and risks of available alternative techniques that do not involve
medical exposure, such as ultrasound or magnetic resonance imaging (MRI).
In justifying each type of diagnostic nuclear medicine examination, relevant
guidelines will be taken into account, such as those established by the WHO.
Nuclear medicine physicians are frequently required to make decisions on the use of
a procedure. In doing so, they should:
 evaluate the potential role of the procedure;
 evaluate the risks and benefits arising from the procedure, (e.g: is there a
good chance of obtaining the necessary information and is it likely to
influence the management of the patient's illness?);
 determine the best procedure to aid in the diagnosis;
 consider the availability of results from previous examinations.
Justification implies that the referring physician and nuclear medicine physician make
the decision on a radiological procedure on the basis of:
 the case history, clinical examination of the patient and clinical laboratory results;
 the availability of nuclear medicine techniques or alternative techniques.
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Any nuclear medicine examination for occupational, legal or health insurance
purposes undertaken without reference to clinical indications is deemed to be
unjustified unless it is expected to provide useful information on the health of the
individual examined or unless the specific type of examination is justified by those
requesting it in consultation with relevant professional bodies.
Mass screening of population groups involving medical exposure is deemed to
be unjustified unless the expected advantages for the individuals examined or for the
population as a whole are sufficient to compensate for the economic and social
costs, including the radiation detriment.
The exposure of humans for medical research is deemed to be unjustified
unless it is in accordance with the provisions of the Helsinki Declaration and follows
the international guidelines for its application and is subject to the advice of an ethical
review committee
As children are at greater risk of incurring stochastic effects, paediatric
examinations should require special consideration in the justification process. Thus
the benefit of some high dose examinations should be carefully weighed against the
increased risk.
The justification of examinations in pregnant women requires special consideration.
Due to the higher radiosensitivity of the foetus, the risk may be substantial.
3.
OPTIMIZATION OF EXAMINATION
Licensees shall ensure that:
1.
medical practitioners who prescribe or conduct diagnostic applications of
radionuclides (BSS II.10–13, 16–18):
 ensure that the exposure of patients is the minimum required to achieve the
intended diagnostic objective;
 take into account relevant information from previous examinations in order to
avoid unnecessary additional examinations; and
 take into account the relevant guidance levels for medical exposure.
1.
the medical practitioner, the technologist or other imaging staff, as
appropriate, endeavour to achieve the minimum patient exposure consistent with
acceptable image quality by:
 appropriate selection of the best available radiopharmaceutical and its
activity, noting the special requirements for children and for patients with
impairment of organ function;
 use of methods for blocking the uptake in organs not under study and for
accelerated excretion when applicable;
 appropriate image acquisition and processing.
If more than one radiopharmaceutical can be used for a procedure, consideration
should be given to the physical, chemical and biological properties for each
radiopharmaceutical so as to minimize the absorbed dose and other risks to the
patient while at the same time providing the desired diagnostic information. Other
factors affecting the choice include availability, shelf life, instrumentation and relative
cost.
The choice of optimal dosage in nuclear medicine is a complex matter.
Today the amount of administered activity is mainly based on local experience and
tradition and there are considerable differences between clinics.
The relation between activity and diagnostic accuracy is highly
dependent on type of examination. It is also important to know whether the diagnosis
is based on quantitative information or on visual evaluation. Both for a simple uptake
measurement and in connection with imaging, the amount of activity needed will
depend on the type of equipment used, the body constitution of the individual patient,
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PART 6. MEDICAL EXPOSURE
the patient’s metabolic characteristics and clinical condition.
The administration of amounts substantially larger than the optimum in
order to improve marginally the quality of the results obtained should be discouraged.
It should also be noted that limiting the administered activity below the
optimum, even for well-intentioned reasons, will usually lead to poor quality of the
result which may cause serious diagnostic errors. It is very important to avoid a
failure to obtain the required diagnostic information; failure would result in an
unnecessary (and therefore unjustified) irradiation and may also necessitate
repetition of the test.
Substantial reduction of absorbed dose from radiopharmaceuticals can
be readily achieved by some simple measures such as hydration and frequent
voiding, use of thyroid blocking agents, laxatives and diuretics.
Equipment shall be operated within the limits and conditions established in
the technical specifications and in the licence requirements, ensuring that it will
operate satisfactorily at all times, in terms of both the tasks to be accomplished and
radiation safety.
For equipment operation, the manufacturer’s operating manual, and the
institutions procedural manual should be followed.
The optimization of the different technical factors involved in a nuclear
medicine investigation should be done for every particular type of examination. This
is to ensure that the available resources are used in the best way.
The data acquisition conditions shall be chosen such that the image quality is
optimum. The choice of collimator, energy window, matrix size, acquisition time,
angulation of collimator, SPECT or PET parameters, and zoom factor shall be such
as to obtain optimum quality image. For dynamic studies, the number of frames, time
interval and other parameters shall be chosen to obtain optimum quality of image
sequence.
The patient should be fully informed about the examination. Patient factors
such as age, disease, size etc. should be considered in the optimisation of the
examination.
4.
GUIDANCE LEVELS OF ACTIVITY
Licensees should ensure that guidance levels for medical exposure are determined
as specified in the BSS, revised as technology improves and used as guidance by
medical practitioners, in order that (BSS II.24):
 corrective actions can be taken as necessary if doses or activities fall
substantially below the guidance levels and the exposures do not provide
useful diagnostic information and do not yield the expected medical benefit to
patients;
 reviews can be considered if activities exceed the guidance levels as an input
to ensuring optimized protection of patients and maintaining appropriate
levels of good practice;
 the guidance levels can be derived from the data from wide scale quality
surveys which include activities of radiopharmaceuticals administered to
patients for the most frequent examinations in nuclear medicine.
In the absence of wide scale surveys, the activity to be administered for each
nuclear medicine procedure should be assessed on the basis of comparison with the
guidance levels specified in the BSS. These levels should not be regarded as a
guide for ensuring optimum performance in all cases.
5.
DOSE CONSTRAINTS
An ethical review committee or another institutional body assigned similar functions
by national authorities shall specify dose constraints to be applied on a case-by-case
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basis in the optimization of protection for persons exposed for medical research
purposes if such medical exposure does not produce direct benefit to the exposed
individual.
Licensees shall constrain any dose incurred knowingly by voluntarily helping
(other than in their occupation) in the care, support or comfort of patients undergoing
medical diagnosis or treatment, and to visitors to patients who have received
therapeutic amounts of radionuclides, to a level not exceeding 5 mSv and 1 mSv per
procedure for adults and children respectively.
6.
EXAMINATION OF CHILDREN, PREGNANT WOMEN AND
LACTATING WOMEN
Several methods of calculating the amount of activity to be administered to a child
have been proposed in the literature. There is no general rule, which can be applied
to all types of examinations. The calculation of the fraction of adult activity to be
administered to a child can be based on body weight, body height, body surface
area, age, organ size or other factors. Some authors suggest one type of activity
schedule for all types of examinations, all based on body weight or body surface area
together with the use of a minimum amount of administered activity, which is
assumed to be the smallest amount of activity required to perform an adequate
examination. Another approach is to develop an activity schedule for the particular
examination. The rationale for the administration of activity should be the same
counting statistics for all ages in order to achieve the same diagnostic accuracy. The
method of achieving the same counting statistics varies with the type of diagnostic
test. For measurements of organ uptake, the total activity in the organ is important.
The licensee shall ascertain whether the female patient is breast feeding.
Cessation of breast feeding is recommended during most nuclear medicine
procedures as many radiopharmaceuticals are excreted in breast milk. Before
administering a radiopharmaceutical to a mother who might be breastfeeding an
inquiry should be made and consideration should be given as to:
 whether the test could reasonably be delayed until after the mother has
ceased breastfeeding
 whether the most appropriate choice of radiopharmaceutical has been made
bearing in mind the secretion of activity in breast milk.
Examples of substitutions that would reduce the dose to the infant (or reduce any
necessary interruption of breastfeeding) are:
 the use of 99mTc-DTPA or gluconate instead of pertechnetate brain scans ;
 the use of 111In-leucocytes instead of 67Ga for sites of infection; and
 the use of pure 123I instead of 125I or 131I.
In order to minimize potential irradiation of a breastfed child, advisory notices
should be posted within the nuclear medicine department asking patients to inform
the staff if they are breastfeeding.
The breast-feeding patient should be informed about the recommendations for
her particular examination in advance of the examination.
7.
RECORDS
According to the BSS (II.31), registrants and licensees shall keep for a period
specified by the Regulatory Authority and make available, as required, the following
records:
(b)
in nuclear medicine, types of radiopharmaceuticals administered and their
activities;
(d)
the exposure of volunteers in medical research.
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PART 6. MEDICAL EXPOSURE
II.32. Registrants and licensees shall keep and make available, as required, the
results of the calibrations and periodic checks of the relevant physical and clinical
parameters selected during treatments
II.19: Registrants and licensees shall ensure that:
- unsealed sources for nuclear medicine procedures be calibrated in terms of activity
of the radiopharmaceutical to be administered, the activity being determined and
recorded at the time of administration;
II.20 (d)
in diagnosis or treatment with unsealed sources, representative
absorbed doses to patients.
8.
REFERENCES
1. INTERNATIONAL ATOMIC ENERGY AGENCY. International Basic Safety
Standards for Protection Against Ionizing Radiation and for the Safety of
Radiation Sources. Safety Series No.115, IAEA, Vienna (1996).
2. INTERNATIONAL ATOMIC ENERGY AGENCY. Model Regulations on Radiation
Safety in Nuclear Medicine. (in preparation).
3. INTERNATIONAL ATOMIC ENERGY AGENCY. Draft Safety Guide on Radiation
Protection in Medical Exposure (in preparation).
4. WORLD HEALTH ORGANIZATION and INTERNATIONAL ATOMIC ENERGY
AGENCY. Manual on Radiation Protection in Hospital and General Practice. Vol.
4. Nuclear medicine (in press)
5. PAN AMERICAN HEALTH ORGANIZATION. Organization, development, quality
control, and radiation protection in radiology services. PAHO Washington D.C.,
(1997).
6. WORLD HEALTH ORGANIZATION, Effective Choices for Diagnostic Imaging in
Clinical Practices, Technical Report Series No. 795, WHO, Geneva (1990).
7. WORLD HEALTH ORGANIZATION, Rational Use of Diagnostic Imaging in
Pediactrics , Technical Report Series No 757, WHO, Geneva (1987).
8. WORLD HEALTH ORGANIZATION, Use of ionizing radiation and radionuclides
on human beings for medical research, training and nonmedical purposes.
Report of a WHO Expert Committee. Geneva, World Health Organization, 1977
(WHO Technical Report Series, No. 611).
9. CIOMS/WHO, International ethical guidelines for biomedical research involving
human subjects. Geneva, Council for International Organizations of Medical
Sciences (CIOMS) in Collaboration with the World Health Organization (WHO),
Geneva, CIOMS 1993
10. INTERNATIONAL COMMISSION ON RADIOLOGICAL PROTECTION Protection
of the Patient in Nuclear Medicine, ICRP Publication No. 52. Oxford, Pergamon
Press, 1987 (Annals of the ICRP 17, 4).
11. INTERNATIONAL COMMISSION ON RADIOLOGICAL PROTECTION.
Radiological protection in biomedical research, ICRP Publication No. 62. Oxford,
Pergamon Press, 1993 (Annals of the ICRP 22, 3).
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12. INTERNATIONAL COMMISSION ON RADIOLOGICAL PROTECTION.
Pregnancy and Medical Radiation. Publication no 84. Oxford, Pergamon Press,
2000 Annals of the ICRP 30, 1)
13. EUROPEAN COMMISSION. Implementation of the Medical Exposure Directive
(97/43 Euratom). Radiation Protection 102, EU, Bruxelles (1999).
14. ROYAL COLLEGE OF RADIOLOGISTS. Making the best use of a department of
clinical radiology: guidelines for doctors. 4th ed. London: Royal College of
Radiologists, (1998).
15. ROMNEY B.M. et al. Radionuclide administration to nursing mothers:
mathematically derived guidelines. Radiology, 1986, 160: 549-554.
16. STABIN, M.,BREITZ, H., Breast milk excretion of radiopharmaceuticals;
mechanisms, findings, and radiation dosimetry, J. Nucl. Med. (2000) 863-873
17. VESTERGREN E, Administered Radiopharmaceutical Activity and Radiation
Dosimetry in Paediatric Nuclear Medicine. Department of Radiation Physics,
University of Göteborg, Sweden (Thesis ISBN 90-6282951-3)
18. WILLIAMS, N.R., et al., Guidelines for the Provision of Physics Support to
Nuclear Medicine, Nuclear Medicine Communications 20 (1999) 781-787. Report
of a joint working group of the British Institute of Radiology, British Nuclear
Medicine Society and the Institute of Physics and Engineering in Medicine
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