Radiation protection differs slightly for the three commonly used forms of sealed sources: Permanent low dose rate implants, Temporary Low Dose Rate Implants, and Temporary High Dose Rate Implants.
Permanent Low Dose Rate Implants
Iodine 125, Palladium 103 and Gold 198
Permanent seed therapy typically uses a low dose rate, and the seeds remain in situ for the rest of the patient's life. The photon energies released by the commonly used seeds (125I and 103Pd) are in the low kilovoltage range and pose minimal risk to the general public in most scenarios.
Radiation Protection during Insertion of Seeds
Permanent 125I and 103Pd seed are typically 'hot loaded', with the radiation oncologist using a template and rectal ultrasound probe to place the seeds at the desired position. These seeds have the advantage of low dose and release of kilovoltage photons; the dose to staff members during insertion is small. 198Au seeds, which were used more frequently in the past, have fallen out of favour due to several reasons - one of these was the increased dose staff received at the time of insertion.
Displacement of Brachytherapy Source
In some cases, a permanent LDR source may become dislodged from the patient. The most common example would be a patient passing a seed in their urine. This represents a potential hazard to the patient and the general public. To prevent serious complications:
- The patient should be advised of this risk
- The patient should be provided with a suitable, shielded container in which to place the source
- The patient should be given the contact number of the radiation safety officer in the event of source dislodgement
This information should be given to the patient in written form.
Death of Patients with Permanent LDR Sources In Situ
The death of a patient who has a permanent source in situ should be notified to the radiation safety officer. The low energy 103Pd and 125I seeds pose minimal risk to staff at funeral homes/graveyards, with the exception of crematory staff. Seeds may survive cremation, presenting a hazard to people who handle the ashes or work in the area. The following recommendations apply:
- For 125I seeds, cremation should be avoided for at least one year after insertion, unless the seeds are removed by a pathologist
- For 198Au seeds, cremation should be avoided for at least one month after insertion
- For 103Pd seeds, no recommendations from ARPANSA exist. However, given their half life of 18 days, midway between that of 125I and 198Au, it would be sensible to avoid cremation for about 6 months
Temporary Low Dose Rate Implants
137Cs, 192Ir (LDR version), 226Ra, 222Rn
Low dose rate implants are less frequent in modern brachytherapy, in large part due to the availability of HDR options that assist with radiation protection.
Care of patients with temporary LDR sources in situ
Unlike the permanently implanted sources, temporary LDR sources have higher photon energies which pose more of a risk to staff. Patients may be immobilised to prevent excessive movement, requiring assistance with normal activities. General guidelines include:
- Specify time limits for staff to be in the room to conform with occupational exposure limits (20 mSv/year, or as low as reasonably achievable). Pregnant or possibly pregnant staff should not care for the patient.
- Staff should personal dosimeters when caring for the patient
- Warning signs on the patient's door and on the bed
- Presence of a shielded container in the event of source displacement
- Visitors should be limited to strict time limits (depending on the source); pregnant women and people under the age of 16 should not visit at all
If the patient is required to leave their room (for emergency care, surgery etc) the source should be removed after checking with the radiation safety officer. Patients should not be discharged if a source is still in situ.
High Dose Rate Brachytherapy
Pretty much just 192Ir nowadays
Remote afterloading techniques allow sources to be placed without staff present in the room, reducing their exposure and allowing high dose rate sources to be used safely. HDR brachytherapy, combined with remote afterloading, removed some of the radiation protection issues associated with LDR sources - including the care of patients on the ward with radioactive sources in situ. However, HDR brachytherapy generates a new set of radiation protection issues, the most obvious of which is that the HDR sources are much more dangerous to the patient and staff if control of them is lost.
Emergency Removal of Sources
A HDR brachytherapy source that becomes stuck inside the patient must be removed within one minute to prevent adverse effects on the patient. Staff using HDR devices should be trained in source recovery regularly so that emergency situations are resolved quickly.
A typical flow chart:
Once the source has been controlled, estimation of dose to the patient and staff should be made. The incident should be reported to the state radiation agency.
