Operational protection in radiotherapy Flashcards
What are some potential accidental and routine staff and other exposures in radiotherapy?
Accidental:
- Individual in bunker when therapeutic beam is on.
- HDR source sent out while worker in room.
- Employee exposure to sealed source in lab (could also be routine).
Routine:
- Low level exposures in the vicinity of radiation installations (e.g. through bunker walls, from linac head etc.)
What must be in place before commencing a new activity involving ionising radiation and what does this include?
Risk assessment:
- Nature of sources.
- Dose rates (from source, routine activities and accidents) including who might be exposed and how.
- Results or previous monitoring.
- Manufacturer’s advice.
- Existing control measures.
- Failure of control measures.
- Systems of work.
- PPE.
- Potential accidents.
List some examples of control measures used in radiotherapy.
Engineering controls:
- Door interlocks (fail to safe e.g. multiple switches working in opposite modes).
- Search buttons (with timing to ensure no button failure or last person not out).
Systems of work:
- Last person out executes search button sequence.
- Room clearance checks prior to exposure.
- Access control.
PPE:
- Pb aprons for CT.
- Handling tongs for sources.
- Brachy seed stand cutting equipment.
- Personal dosimetry.
What differences are apparent with warning signage/lights and emergency stops for diagnostic radiology and radiotherapy?
Diagnostic radiology:
- Warning signage/lights outside of room at entry and on equipment.
- Emergency stops on equipment and sometimes at other points in room.
Radiotherapy:
- Warning signage/lights also at various locations within room so a sign can be seen at all points within room.
- Emergency stops place around the room such that approach to the machine/beam is minimised.
What system of work could be employed to protect engineers performing maintenance on activated linac head components?
Maintenance must not be started with 30 minutes of the end of a radiation exposure.
What control measures can be used to prevent accidental exposures in linac bunkers with equipment rooms behind the gantry or areas that cannot be seen from the door?
- Placing search buttons in locations that ensure those areas have been searched prior to leaving the room.
- Interlocking doors such that the equipment door interlock must be made before the main door interlock is made.
What control measures can be used to minimise risk for non-radiation workers (e.g. cleaners) entering a linac bunker?
- Warning signage.
- Room state indicator (e.g. indication when room is not in use).
- Key control procedures to ensure keys are not left in console area.
- Training and systems of work to allow for non-radiation workers to know when and where they can work.
What document should contain contingency plans?
Local rules.
How is it decided who should be monitored? Who is typically monitored in a radiotherapy department?
- Risk assessment.
- Therapeutic radiographers, although not monitoring could be justified for this staff group with historical monitoring.
- CT radiographers: Assisting patients during scan and lack of door interlocks.
- Maintenance engineers: Exposure to activated components and klystron.
- Physics staff: Work with sources, work with equipment at commissioning etc.
When may workers need to be classified in a radiotherapy department?
- Handling of radioactive sources for implantation.
- Scanning patents with PET sources.
What differences are apparent with the handing back of a controlled area in radiotherapy when compared to diagnostic radiology?
Restricted hand back may be undertaken when a parameter is within tolerance but is predicted to be out in a few weeks. In this case, equipment can be used in a restricted manner but corrective action must be undertaken within a set period of time or the equipment be removed from use.
What may be required in relation to the Environmental Permitting regulations for a radiotherapy department?
- Permit to hold/dispose of brachytherapy sources.
- HASS permit for brachytherapy after loader.
