Radiation protection in endovascular brachytherapy
Endovascular brachytherapy
Endovascular brachytherapy (EBT) is a treatment modality to prevent restenosis of coronary arteries of the heart and blood vessels of the extremities after the original stenosis, or blockage, was opened by angioplasty. It has been proven that radiation decreases the occurrence of restenosis. The sources used in endovascular brachytherapy have a much lower strength than HDR sources but radiation safety is still a critical issue.
Frequently asked questions on optimization and safety of EBT
» What sources are used in EBT?
» Is my treatment lab sufficiently shielded for EBT?
» How do I know that the source has been placed in the correct location in the patient?
» Is there a risk for calculation mistakes leading to unintended absorbed dose?
» What should I do if the normal return movement of the EBT source fails?
» What if the emergency source retraction system also fails to retract the source?
» What sources are used in EBT?
Several types of beta-emitting and gamma-emitting sources have been used in EBT, such as double-layered balloon catheters with a radioactive coating between the layers, balloon catheters filled with a radioactive liquid or gas, ribbons or trains of sealed radioactive sources, radioactive wires and radioactive stents. These sources are generally used for coronary endovascular brachytherapy, but standard remote afterloading devices with gamma-emitting radionuclides can be used for peripheral endovascular brachytherapy. Since irradiation is targeting to parts of the arterial wall to a depth of 0-3 mm, sources are mainly beta ray or low-energy gamma ray radionuclides.
» Is my treatment lab sufficiently shielded for EBT?
A qualified expert in radiotherapy physics should determine this.
It is common for EBT of coronary arteries to be performed in catheterisation labs, which might not have been initially designed for radioactive materials, but to protect against X radiation. If beta sources are used in the treatment, no room shielding is generally needed but if gamma ray sources are used it is likely that shielding will be needed. In particular, some endovascular treatment of peripheral vessels might be performed using standard HDR brachytherapy equipment, which would necessitate dedicated HDR treatment rooms with high shielding requirements. A qualified expert in radiotherapy physics should be engaged to ascertain the fulfilment of shielding requirements.
» How do I know that the source has been placed in the correct location in the patient?
The actual position of the source inside the patient should be verified by real-time fluoroscopy during the procedure. A radiation survey outside the patient is not sufficient. If there is a discrepancy between the planned and the actual location that cannot be rectified by further source movement, but by pulling the source back into the delivery device. Before putting the catheter in place, it a visual inspection is needed, also for mechanical integrity using a non-active dummy source. Kinks in the catheter may lead to accidental exposure, as shown in reports of catheter kinks leading to unintended dose distributions in endovascular brachytherapy.
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» Is there a risk of calculation mistakes leading to unintended absorbed dose?
Yes - you should ensure independent verification of calculations.
As in all radiotherapy, there is a risk of mistakes in the calculation of treatment times. An example of this was reported (IAEA TECDOC 1488) where the diameter of the artery was used for calculation purposes instead of the intended radius, causing a near doubling of the intended absorbed dose to the patient. Endovascular brachytherapy is a discipline where the time between determination of treatment parameters, treatment planning and treatment delivery is very short and, thus, where there is a potential for mistakes being made due to unclear communication. As always, calculations need to be independently verified.
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» What should I do if the normal return movement of the EBT source fails?
You should follow the local emergency procedure.
It is very important that a local emergency procedure is put in place for this type of emergency situations, already as part of the clinical commissioning of the EBT procedure. This procedure should be well posted, known by staff and tests should be performed.
Source return can fail due to breakdown of power backup, failure of mechanics or obstructions in the catheter. The built-in emergency source retraction system should be used to position the source inside the storage container of the delivery device. It is important that persons not directly involved in the emergency procedure leave the room.
» What if the emergency source retraction system also fails to retract the source?
You need to manually remove the source from inside the patient.
Appropriate emergency containers in the treatment room are always needed – plastic shielded containers for beta sources and lead containers of appropriate thickness for gamma sources.
An emergency procedure is needed, with the following instructions:
- Try to locate the source by using X-ray fluoroscopy.and remove the catheter from the patient, taking care to avoid touching the catheter near the active source;
- Use emergency equipment, such as forceps, tongs or tweezers, to move the catheter to the emergency container (which might be handled by another person for practical reasons).
It is important that persons not directly involved in the emergency procedure leave the room.