There are numerous roles that must be filled before unsealed sources are used in diagnostic or therapeutic procedures:
- A responsible person who oversees radiation matters in the state
- The nuclear medicine physician who makes clinical judgements regarding use of the unsealed source
Note: Not a radiation oncologist…
- A nuclear medicine technician (who may also be the administering person), involved the preparation, imaging or administration of the unsealed source
- A nuclear medicine physicist who is able to perform dosimetry and advise on radiation protection
- The radiation safety officer (who may be any of the people above) who oversees radiation protection issues
Radiation Protection Issues in Unsealed Source Therapy
The IAEA handbook lists stages where radiation protection must be considered:
- Pre-treatment: Consideration of pregnancy
- Day of treatment: Administration guidelines, advice to nursing staff, preparation of patient room
- During treatment: Patient care (contaminated fluids, visitors), emergency situations
- Discharge: Discharge limits, patient information, room cleaning
- Post-discharge: Advice on future pregnancy
Some treatments (131I) administer a significant quantity of unsealed source which decays over ; these patients must be kept isolated to minimise exposure to the general public during this time. A specialised room must be available for the care of these patients, including:
- Single room
- Ensuite toilet/shower with waste disposal directly to the main sewer
- Walls and floors constructed of non-porous material; edges covered to allow easy cleaning
- Barrier to prevent entry into the room (eg. a door), appropriately signed to advise:
- That radiation is present
- That pregnant women should not enter the room
- That nothing should be removed from the room unless cleared by medical physics
- That protective clothing should be worn
A supply of disposable gloves, gowns and footwear should be available outside the room.
All staff who perform duties within the room should wear a personal dosimeter; preferably electronic. Only essential duties should be performed and nothing is to be removed from the room.
It is generally easier to use disposable cutlery/crockery for the patient to avoid the need for decontamination. Patients who are unable to self care should not receive an unsealed source due to unacceptable dose to carers.
For emergency procedures, see below.
Patients must take some responsibility when they are administered an unsealed source. This includes:
- Not leaving their room unless there is an emergency
- Only using the toilet and shower facilities in their room
- Not using their own bed linen / clothing to prevent contamination
Discharge following Unsealed Source Administration
Patients should not be discharged if they have significant activity remaining inside them. This is an issue with two commonly used radionuclides:
- Iodine 131 may be administered with activity up of to 7.5 GBq (although doses of 1 - 4 GBq are more common) for the treatment of thyroid cancer. With a physical half life of 8 days, this means that for several days there is a risk of increasing another persons dose above the recommended limit of 1 mSv / year. Australian guidelines state that an informed carer is able to exceed this limit, up to 5 mSv/year. Patients must therefore be admitted for several days until the activity within their body has dropped to < 600 MBq. This can be checked by measuring the dose rate at 1 m from the patient - it should be under 0.07 mGy/hr.
- Samarium 153 has a short half life of just under 2 days, which decays through beta emission (about one quarter of decays also result in gamma radiation of maximum energy 103 keV). Patients are usually administered 37 MBq/kg of 153Sm; which is also excreted through the urine. After one void, the dose rate outside the patient has usually fallen to negligble levels, but this should be checked; two voids are preferable. The maximum dose that may be administered to an outpatient is 4000 MBq.
- Strontium 89 has a relatively long half life of 50 days; however it localises well to bone and unlocalised strontium is usually excreted after 48 hours. As a beta emitter, it presents little risk to other people aside from contamination of clothing. The dose is usually 2 MBq/kg; the maximum dose for outpatient treatments is 300 MBq/kg is not normally reached.
Unsealed Sources and Pregnancy
Unsealed sources, particularly radioactive iodine, can give dose to the foetus from within the mother or through crossing of radioaactive particles through the placenta and into the foetus itself. There are two types of effects seen in the foetus:
- Deterministic effects, more common in early pregnancy, associated with miscarriage (before implantation), congenital abnormalities (during organogenesis), or growth restriction, microcephaly and mental retardation (after organogenesis; risk falls after 20 weeks). The threshold dose for these effects is in excess of 100 mGy.
- Stochastic effects, including an increased risk of cancer (esp. leukaemia as a child), and the possibility of the induction of hereditary effects in the child's future children. There is no threshold for these effects, but the risk becomes detectable with doses over 10 mGy.
Diagnostic Unsealed Sources and Pregnancy
Rarely it may be necessary to perform a diagnostic nuclear medicine test on a pregnant woman. The best solution is to avoid the test until the pregnancy is over; however this may not be practical. Most nuclear medicine investigations result in dose to the foetus from collection in the mother's bladder (eg. most Technetium 99m tests). Iodine may be taken up by the foetal thyroid; administration of 131I in any form after 10 - 12 weeks is a contraindication.
Therapeutic Sealed Sources and Pregnancy
Women should not be pregnant if a therapeutic source is to be used. The most common source involved in this situation would be 131I. Doses to the foetus may be elevated above the threshold for deterministic effects. To avoid this:
- Women should be advised over the risks of pregnancy and unsealed source therapy prior to treatment commencing
- Women should advise the treating team if they have become pregnant before receiving the unsealed source
- A beta-HCG test must be performed within 24 hours prior to dose administration to ensure that no pregnancy is present.
- Women should be advised to avoid falling pregnant for a certain time after administration of an unsealed source, depending on the half life of the source
Australian guidelines state:
- A restriction period of 4 months for radioactive iodine therapy
- A restriction period of 24 months for 89Sr therapy.
- No restriction following 153Sm therapy (although…)
Special Protection Issues for Unsealed Sources
Contamination of the environment may result from three situations:
- Leakage of the source from its storage container
- Leakage of the source during administration to the patient
- Leakage of fluid from the patient
The most important piece of equipment in the event of a spill is the decontamination kit, which should be on hand wherever unsealed sources are in use. This kit should contain protective equipment, towels for absorbing liquid, warning signs and markers to denote the contaminated area. Personal dosimeters and survey meters should also be available.
If a spill occurs:
- The first step is always the safety of the patient.
- Involved staff should vacate the immediate area (not too far; avoid spreading of contaminated liquid)
- Eg: If the spill occurs in a room, staff should leave the room to a neighbouring room, but not trek through the entire department
- The radiation safety officer should be called immediately and the decontamination kit brought to the site
- Staff should equip protective clothing (gloves at least)
- The spilled liquid should be contained by using absorbent material (preferably paper towels) which can then be discarded. If the spill originated from a container, that container should be righted.
- The area should be marked out by the physicist; hot spots should be noted
- If areas remain hot following removal of liquid, they should be cordoned off.
- If equipment is contaminated, it should be stored until the contaminating material has decayed.
Management of spills is dependent on the unsealed source involved. Strontium 89 has a half life of 50 days; whereas Samarium 153 only 2 days. It may be appropriate to seal off the samarium 153 area; whereas closing off of an area contaminated with Sr89 may be impractical.
Once the source is controlled, steps must be taken to determine the dose received by staff and the patient. Counselling should be given.
The Unwell Patient
Patients who have received an unsealed source for a diagnostic procedure typically pose a low level of risk to carers; gloves are suitable to prevent contamination of the skin.
Patients who have received a therapeutic dose of a radionuclide and become unwell present more of a challenge, which depends on the emergency. The patient's health is most important; radiation protection issues should be considered but should not prevent the administration of care.
Patients requiring cardiopulmonary resuscitation must receive this (if medically appropriate). Only staff actively resuscitating the patient should be involved. Mouth to mouth resuscitation is to be avoided. If transfer to intensive care is required, the patient should be placed in an isolated room where possible and medical/nursing staff advised of the risk of contamination. Only essential investigations and procedures should be performed.
Patients who require surgical intervention should have this delayed if possible. If the need is urgent, the surgical team should plan the procedure in advance to minimise the time spent operating. Double gloving reduces dose to the hands. Avoiding standing near the organs containing a high dose is advisable.
Following surgery, equipment should be checked for contamination and stored appropriately
Management of staff
If contamination of staff with 131I has occured, iodine should be administered. This iodine competes with the radioactive iodine in the thyroid and reduces uptake; it therefore reduces the risk of stochastic effects occuring in the thyroid gland. Estimation of dose and risks should be provided to all staff.
Back to physics