Dose Reconstruction for Industrial Radiography - HPS Chapters
Transcript of Dose Reconstruction for Industrial Radiography - HPS Chapters
Outline• Purpose of a dose reconstruction
oGoals and objectives
• Anatomy of a dose reconstruction
oGathering evidence
oPutting together the pieces
oCommunicating results
Purpose• The purpose of a dose reconstruction is to estimate the
most probable doses to whole body, lens of the eye, and
organs (e.g., skin).
• The data may be used to assign a dose to an
individual(s).
• The data may be used as part of an incident report to
regulators.
• The data may be used by physician(s) for monitoring
biological response and treatment planning.
NOT the Purpose
• The dose reconstruction is NOT intended
to:
oPlace blame for the incident
oOpine on apparent regulatory violations
Challenges• Involved individual(s)
oFear of possible biological effects
oFear of being found negligent
oFear of legal ramifications or job loss
oReliance on memory of events
Challenges (continued)• These fears can affect the quality of your dose
reconstruction efforts because:
o Person doesn’t want to believe that they may have
been harmed so they alter description of events to
minimize their potential exposure
o Person knows they did not follow proper protocol so
they provide information that conflicts with evidence
o Management suppresses or refuses to answer
questions because:
• afraid of losing contract
• legal repercussions
Approach• Written attestation from individual(s) involved.
o Step-by-step description of their actions with respect
to proximity to equipment.
o Walking, bending, climbing, etc.
• Equipment
o source activity, type, thickness of guide tubes, etc.
• Dosimetry results
o Description of where dosimeters are worn
o Results from processor
Approach (continued)• Individual Characteristics (depends on incident)
oHeight
oWeight
oHand size
oOverall general health
• Working environment conditions
oObjects (shielding purposes)
oWeather
The source
Iridum-192 Maximum activity depends on camera. Rated up to 150 Curies
Activity given isOutput.Actual activity is1.4 times greater.
Re-enactments
• Re-enactments are key sources of information.
• Measure walking speeds (repeat and take upper and lower bounds)
• Time how long it takes to perform certain activities (repeat and take upper and lower bounds)
• Measure distances between source location and body regions for each re-enactment step and use as upper and lower bounds)
• Review reported actions with another qualified radiographer to determine if steps make sense
Example
To save time, worker has habit of not retracting source all the way into safe position
in shield so he can do multiple shots without having to “unlock” the source for each
shot.
1. Sets up for shot.
2. Performs x-ray of weld
3. Retracts source counting revolutions and stops just before he thinks the lock
will engage
4. Walks up to x-ray cartridge, sets cartridge aside.
5. Removes collimator with guide tube and places on next location for next shot.
6. Walks back to camera, decides to eat lunch first before shot.
7. Decides to take camera with him back to truck.
8. Approaches front end of camera and disconnects guide tube.
9. Pulling back guide tube, sees source.
10. Drops everything and retreats.
11. Brings source back to “safe” condition.
12. Calls RSO
Example (continued)
No alarming dosimeter
No PIC
No handheld meter
No ring badge
Yes Landauer dosimeter on waist
What you don’t know!
1 How much exposure on dosimeters prior to
incident
2 “Shadow” effects on badge
3 Badge orientation to radiation fluence
Summary
1. Create a step-by-step re-enactment of incident of very
detailed account considering:1. TIME
2. DISTANCE
3. SHIELDING
2. Takes lots of pictures
3. Using estimates of time, distance and shielding, use
Microshield to calculate the exposure to the dosimeter
and match to readings to see if your estimates are
reasonable.
4. Create upper and lower bounds of possible dose for each
step.
5. Add lower and upper bounds for each step to estimate
possible total lower and upper bounds.
6. Include all information in a written report and estimate the
“most probable dose.”