Radiation protection of patients in therapeutic nuclear medicine
Frequently asked questions by the health professionals
» What information should I get from the patient before administering the radiopharmaceutical?
» How do I know the absorbed dose given to the treated organ?
» How do I know what activity to give when the referring physician has prescribed an absorbed dose to the thyroid?
» What are the radiation risks for relatives and caregivers after discharge?
» How to deal with death of patient after radionuclide therapy?
» Will the patient trigger a security alarm at airports or other public places?
» One example of an accident
» What information should I get from the patient before administering the radiopharmaceutical?
Before treatment, the patient should be carefully identified, following normal hospital routine. The patient should also be interviewed in order not to forget important information necessary for safe treatment. The interview should include questions about pregnancy, breastfeeding, incontinence, nausea, type of work, use of public transport and living conditions. The information provided by the patient will determine how the therapy should be administered and what restrictions in the patient’s daily life are necessary in order to reduce the exposure of other people.
If it is anticipated that the patient will be unable to perform activities of daily living, will be confused, will become incontinent of urine, will have nausea or vomiting, or has other conditions which could complicate the course of post-treatment management, the nuclear medicine department and the RPO shouldinform and advise the patient. Laboratory procedures requiring urine or blood specimens should be performed before the treatment is administered.
Oral and written explanations of the therapy are useful to help the patient understand the nature of the treatment and any risks to the patient or other persons. It is the responsibility of the medical practitioner to perform this and to discuss it in detail with the patient. This procedure should also be recorded in the patient’s medical record. Examples of patient information sheets to be used in treatment with iodine-131 are given below.
Patient instruction card (pre-therapy):
I-131 Therapy - What is it all about?
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What is an I-131 therapy dose for? ! I-131 therapy detects and treats any areas of residual thyroid tissue or tumour. Is any preparation required? ! For at least 1 month prior to I-131 therapy you must not have had iodine containing preparations (certain vitamin tablets, cough mixtures and kelp tablets) or iodinated contrast agents used for X-ray angiograms and CT scans. ! Thyroid hormone medication will also need to be stopped for approximately 6 weeks before therapy. This will be arranged by your own doctor. ! In addition, you require certain blood tests on the morning before I-131 administration (to check whether any residual thyroid tissue is adequately stimulated, and a pregnancy test if you are a woman of childbearing age). These tests will be organized by your own doctors. ! The I-131 therapy dose is administered while you are in the hospital. A hospital bed will be arranged for you. Very important! If you are, or could be, pregnant or are breast feeding, please notify staff before proceeding with the therapy dose. You must also not become pregnant for at least 6 months after the I-131 therapy dose. What does an I-131 therapy dose administration involve ? ! You will be admitted to a single room. A drug may be given to you prior to I-131 therapy to prevent potential nausea. ! A doctor and a technologist will come from the Department of Nuclear Medicine to administer the therapy dose. The doctor will check certain details (such as the date of surgery, and the result of any blood tests you may have had). ! You will then be asked to swallow a capsule containing the iodine-131. This radioisotope is accumulated by areas of thyroid tissue and destroys these areas. |
! The I-131 causes very few side effects. You may experience some minor neck discomfort over the first few days. No other discomfort is likely, though you need to remain in an isolation room for an average of four days. ! The isolation room is used to limit radiation exposure to other people. You will be instructed about certain simple precautions to undertake. ! The hospital's radiation safety officer will check your radioactivity level and will decide when you can be discharged home from hospital (usually three days after admission). ! Before you are discharged, you will be brought to the Department of Nuclear Medicine where images of your body will be taken from various angles. Further delayed views may also be necessary. ! When you are sent home, you will be instructed as to certain simple precautions to take over at least the next 7 days. Any additional precautions will be discussed with you. 1. Avoid close or prolonged contact with pregnant women or very small children. A good guide is to stay more than one arm’s length away from people. 2. Avoid unnecessary trips on public transport and attending public entertainment (you could be sitting next to someone pregnant). 3. Flush toilet twice after use. Wash hands copiously. 4. Do not attend work if this involves prolonged contact with people. 5. If convenient, sleep in a single bed if partner is less than 50 years of age. 6. Wash hands carefully before preparing food. Do not share your utensils with other family members and avoid activities which may involve exchange of saliva (e.g. kissing). 7. If you are admitted to hospital within 4 weeks of the dose, please arrange for the Nuclear Medicine Department to be notified.
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Patient instruction card (post-therapy):
The following is an example of an information card which should be given to the patient at the time of discharge, and which the patient should carry with them at all times for as long as the hospital has recommended (usually up to 4 weeks):
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This card should be carried at all times until (date). Patient name: Address: Treating hospital: Hospital record number: Treating doctor: Radionuclide and form: Activity: Administered on (date): In case of difficulty, please contact: Telephone: |
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Patient instructions:
Signed: Date: |
» How do I know the absorbed dose given to the treated organ?
This information is often not easily available for the individual patient. In order to calculate radiation absorbed dose to the treated organ, requires information such as administered radioactivity, the individual’s uptake measurements, additional biokinetic data, as well as the mass of the treated tissue or organ. Such calculations can be made using methods of the Medical Internal Radiation Dosimetry (MIRD) committee or the International Commission on Radiological Protection (ICRP). This clinical dosimetry should be conducted by qualified individuals such as a medical physicist.
» How do I know what activity to give when the referring physician has prescribed an absorbed dose to the thyroid?
This calculation must be determined by a qualified individual.
It will require uptake measurements at different times after administration of a trace dose of Iodine-131, the individual biokinetic data can be determined. The volume of the organ can be estimated using one of several imaging technologies such as a gamma camera or ultrasound. These measurements should provide enough information to determine the activity to administer to the patient in order to reach the prescribed radiation absorbed dose. This is an area of major research activity due to the many imaging technologies and imaging drugs, therefore the most current methods can be found in the literature.
» What are the radiation risks for relatives and caregivers after discharge?
After discharge, the patient may be independent and able to carry on a normal life. In some cases, the patient will need care and assistance with daily tasks such as mobility and feeding. It is the patient's family, or an external caregiver such as a community nurse, who would be providing this care.
International bodies such as the IAEA and ICRP provide guidance on radiation dose limits to both radiation workers and the general public. Within these limits, there are allowances for this situation. The ICRP states that "medical exposure is confined to exposures incurred by individuals as part of their own medical diagnosis or treatment and to other exposures ... incurred knowingly and willingly by individuals in the support and comfort of patients undergoing diagnosis or treatment."
The IAEA further requires that the effective dose to any comforter or visitor (i.e. caregivers and family) should be unlikely to exceed 5 mSv during the period of the patient's treatment. For children, the level should be less than 1 mSv/yr.
The various national and international discharge guidelines are designed to provide compliance with these recommendations.
» How to deal with death of patient after radionuclide therapy?
At the time of discharge, the therapy facility should provide the patient with a small card describing details of the treatment and contact information for a radiation protection officer (RPO) to consult in an emergency.
In some cases, especially palliative treatment, the patient may die shortly after the treatment. Areas of concern arise with respect to embalming, burial or cremation of the corpse and the conduct of autopsy examinations. National regulations, some quite dated, are available for some or all of these in many countries, but there is a lack of international consensus recommendations. Practice tends to be guided by a mixture of custom, professional guidance and national regulation.
The authorities in some countries place limits on radioactivity that may be present in the corpse before embalming, burial or cremation. In the case of death of a patient within a few months after therapy, consult the therapy facility’s RPO to determine the amount of activity remaining in the patient. No special precautions are required, provided that the activity remaining in the corpse is not in excess of national limits. If the activity remaining in the body is greater than national limits, or if national limits have not been established, the RPO should determine the radiation precautions to be followed. The precautions should be based on dose limits, a generic safety assessment of the need for monitoring personnel who carry out these procedures, the need for monitoring the premises, the need for minimizing external radiation exposure and the potential for contamination.
It should be noted that there may be significant variations between countries and it is advisable to establish an approach consistent with local requirements. In addition, it may be necessary to take account of developments in regulatory practice, particularly vis-á-vis dose limits and dose constraints that have been introduced after some of these radioactivity limits were established.
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» Will the patient trigger a security alarm at airports or other public places?
Current international security measures such as those in place at airports and border crossing points may include extremely sensitive radiation detectors. It is quite possible that patients treated with gamma-emitting radionuclides could trigger these alarms, particularly in the period immediately following discharge. Triggering of an alarm does not mean that the patient is emitting dangerous levels of radiation - the detectors are designed to detect levels of radioactivity far below those of concern to human health. For example, it is possible to detect 0.01 MBq of Iodine-131 at a distance of 2-3 m. This is a tiny fraction of the recommended discharge level in a patient.
The security authorities are well aware of this possibility, and if a patient is likely to travel soon after discharge, the hospital or the patient's doctor should provide a written statement of the therapy and radionuclide used for the patient to carry with him. The security staff are often unlikely to have any training for this occurrence, so patients should be advised to either avoid such travel or be prepared to experience some inconvenience.
A patient was referred for treatment of Graves' disease with 555 MBq of Iodine-131. The radiopharmacist assumed that the administered activity would be 1073 MBq rather than 555 MBq, since 1073 MBq of administered activity is what was routinely used for Graves' disease in that hospital. He therefore requested 1073 MBq of activity from a commercial radiopharmacy. The activity received was 1058 MBq. When the radiopharmacist logged the activity into the computer after being measured by a dose calibrator, he failed to realize that the referring physician’s prescription was only for 550 MBq. Furthermore, the physician who actually administered the isotope also failed to check the prescription. As a result, the patient's thyroid received a radiation absorbed dose of about 319 Gy instead of the intended 167 Gy, an overdose of 91%.
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