Dose Reconstruction for Industrial Radiography

Incidents

Christopher B. Martel, CHP

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

Nice working conditions

Too Close!

Not very nice working conditions

The Equipment

QSA Global Model 660 and 880

The source

Iridum-192 Maximum activity depends on camera. Rated up to 150 Curies

Activity given isOutput.Actual activity is1.4 times greater.

Iridium-192

Cobalt-60

Reconstructing the incident

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.”