Response to an Event at a
Medical Cyclotron
Presentation to North Carolina Health Physics Society
By Christopher Martel, CHP
Director, Radiation Safety Officer
Brigham and Women’s Hospital
and
James P. Tarzia, CHP
Executive Director
Radiation Safety & Control Services, Inc.
What happened?
 Radiochemist was exposed to vial containing
1.6 Curies of F-18 in contact with his upper
arm.
 Preliminary dose estimate was 50 – 100 Rem
to upper arm (included in definition of “Whole
Body” and TEDE).
 Reported to senior management within two
hours of event and a lot of people decided to
“jump in.”
How could this have happened?
 Late May 2009, the delivery line for F-18 was
redirected to dispense F-18 from Hot Cell #2
to Hot Cell #4.
 Line was not returned to original
configuration.
 June 30, a F-18 run was made in the
Cyclotron, and was intended to be dipsensed
to Hot Cell #2, but because of earlier change,
the dose was dispensed to Hot Cell #4.
How could this have happened?
 Radiochemist was working in Hot Cell #4
setting up QC equipment for F-18 while dose
was being dispensed from Cyclotron.
 1.6 Curies was dispensed into a vial that was
held in a container in Hot Cell #4.
 Worker’s upper arm was in contact with the
container during and after the F-18 was
dispensed.
What didn’t happen!
 By procedure, no work to be done in any hot cell
while dose is being delivered!
 He though it was okay – he wasn’t in cell #2
 Must wear alarming electronic dosimeter when
working in production area!
 Didn’t like it. Alarm level too low! Kept
alarming!
 Must have working meter in area while working in
production area!
 Plug in meter inoperable. Replaced with
handheld and left on, so batteries died.
Where it was supposed to go
 FASTlab located in Hot Cell #2
Where it went
Closer view
Showing scale and perspective
During re-enactment
Type of vial in container
Timeline – Day 0
 Call received at 12:30 that at 11:30 the event
occurred. The cyclotron engineer estimated
dose to worker as about “500 millirem.”
 RSO investigated.
 Verified activity
 Removed all activity from hot cell
 Worker showed us what he did (reenactment)
 Dose appeared to occur to upper arm
 Dosimetry collected and sent in for immediate
processing. No more access to restricted
areas.
Initial Information Gathered
 Initial reported information:





Activity – 1.6 Curies F-18
Delivery time into vial – < 30 seconds
Exposure time – 4 minutes
Distance to upper arm – 2 cm from vial with
shielding from with container
Distance to upper arm – 4 cm no shielding if
arm on top of container
Estimated Dose
 Using data from preliminary information:
R  cm2
1hr
R  cm2
( F  18)  6
1,600mCi 
 2.67
hr  mCi
3,600 sec
sec
R  cm 2
1
2.67

 210 sec  140 Re m
2
sec
2cm
3mm Lead shielding in container
0.69 *140 Re m  96.6 Re m
Uh oh!!
Next sequence of events
 Reported to Senior Management that an
event occurred.
 Under current regs, it may very well be an
overexposure. Dose may be 100 Rem to
upper arm. So, if


extremity dose – 2 times annual limit 100 Rem
whole body dose – 20 times annual limit
 At 4:30 – report to state (and hope no one is
around!) Too bad! One lone person in office.
We made the NRC event page!
General Information or Other
Event Number: 45176
Rep Org: MA RADIATION CONTROL PROGRAM
Licensee: BRIGHAM AND WOMEN'S HOSPITAL
Region: 1
City: BOSTON State: MA
County:
License #: 44-0004
Agreement: Y
Docket:
NRC Notified By: TONY CARPENITO
HQ OPS Officer: VINCE KLCO
Notification Date: 06/30/2009
Notification Time: 17:27 [ET]
Event Date: 06/30/2009
Event Time: 11:30 [EDT]
Last Update Date: 06/30/2009
Emergency Class: NON EMERGENCY
10 CFR Section:
AGREEMENT STATE
Person (Organization):
JAMES TRAPP (R1DO)
DUNCAN WHITE (FSME)
Event Text
AGREEMENT STATE REPORT - POTENTIAL WORKER OVEREXPOSURE
The following information was received via facsimile:
"A worker was working in a hot cell when a F-18 [radio-isotope] was mistakenly delivered to the hot cell. [The] initial estimated worker
dose [was] 100 Rad extremity dose and 20 Rad to the whole body (upper arm). The dosimeter has been sent to Landauer for
immediate processing. [The] worker has been taken off Rad work and is being monitored"
A Commonwealth of Massachusetts investigation is pending.
Nightmare!
 Someone tells others possible 100 rem whole
body dose!
 Occupational Medicine gets involved.
 Hears 100 rem whole body dose.
 Requests assistance from Radiation
Oncology physician.
 He tells occupational medicine – “We need to
get this person into the emergency room stat
and pull blood samples!”
Day 1
 Big Meeting:





Senior Management
Risk Management
Occupational Medicine
Workers involved in event
Me
 Radiation Oncologist stated that what I did
(worker interview and re-enactment) was
“harsh” and that I caused “psychological
trauma” to the individual.
Day 1 (continued)
 More information gathered.
 Time of actual exposure was less, probably
on the order of two minutes based on
sequence of events (dose delivery versus call
from cyclotron engineer to have chemist
verify dose was delivered).
 Could the distance from vial to arm have
been further? Deep dose 1 cm into arm?
 Should I use upper arm as extremity or whole
body?
End of Day 1
 I’m on dangerous ground!!
 I better hire someone else to do this so I don’t
unintentionally bias, or give the impression
that I manipulated the results!
 Hire someone else and let them do an
independent evaluation!
Independent Dose Evaluation:
Our Mission
To calculate a legally defensible dose to the worker
which represents accurate risk and:
1. Is derived from an accurate representation of the
exposure situation,
2. Has a sound technical basis founded on accurate
parameters and current acceptable dose
calculation methodologies, and
3. Contains an appropriate and defendable amount
of conservatism
Analyzing the Event
 Interview with RSO
 Interviews with workers
 Determination of physical parameters

Vial and line volumes, shield thicknesses, etc.
 Determination of time and distance
parameters

Detailed controlled mockup of transfer and
worker position
Event Facts Discovered from
Analysis – Delivery Line
 The expected radioactivity transferred to the vial was 1.6
Curies which was confirmed by assay.
 The internal diameter of the delivery tube was 1/32 inch
(0.079cm) and a critical length of less than 3 feet (91.4 cm)

Maximum possible in tube: 0.4826 Ci
 The delivery tube extended approximately 12 inches (30.48)
up from the top of the vial and then looped back toward the
rear of the hot cell.
 Whole body exposure to the worker from the rear line loop
was most likely not closer than 15 cm.
 Total time to transfer liquid to the vial was 40 +/- 3 seconds.
Event Facts Discovered from
Analysis – Receptor vial
 The vial contained 10 ml of non-radioactive aqueous




solution prior to the transfer.
An additional 1.5 ml of radioactive solution was
added to the vial containing the F-18.
The total radioactive solution in the vial was
contained in a cylindrical shape with a radius of 1.64
cm and 1.90 cm tall.
The vial shield was composed of 0.40 cm of lead and
0.30 cm of steel.
Maximum possible air gap between the vial and the
inside of the shield was approximately 2 cm and the
minimum air gap possible was approximately 0.3 cm.
Event Facts Discovered from
Analysis – The Worker
 The work performed in Hot cell #4
required the worker’s upper left arm
to be positioned against the shield
that contained the vial to which the F18 was dispensed.
 Distance from the vial to the workers
chest dosimeter was approximately
15 inches (38.1 cm).
 The hot cell worker was performing
maintenance in Hot Cell #4 for the
entire duration of the radioactive
solution delivery.
Hot Cell #4 with Shielded Vial and
Delivery Tube
Dose Calculation Process
 Validate initial bounding calculation
performed by RSO
 Perform detailed modeling of dose delivery
 Evaluate calculated results against dosimetry
results and risk to worker
 Refine dose calculations using more
appropriate risk-based techniques
Validation Result
 Bounding calculation performed by RSO was
validated using modeling techniques but
overestimated worker risk from TEDE



Bounding calculation used TEDE=DDE (upper
arm)
Not a uniform exposure to the whole body
Dose to upper arm is not consistent with
actual whole body risk for non-uniform
exposure – NRC Guidance
NRC 10CFR20 Guidance
The NRC states in
10CFR20 that the organ
dose weighting factors
prescribed in
10CFR20.1003 may be
used “for external
exposures on a case by
case basis until specific
guidance is issued”
NRC Regulatory Information
Summary
In February 2003, NRC
issued a Regulatory
Information Summary
encouraging licensees to
use the effective dose
equivalent in place of the
DDE in selected situations
that include cases where
“the doses are calculated
rather than measured with
personnel dosimetry”.
TEDE Calculation using EDE
 Received concurrence from State on approach
 Used methodologies developed by Dr. X. George
Xu at Rensselaer Polytechnic Institute
 Monte-carlo calculations of the EDE rate for photon
emitting particles located on 74 different skin
locations of the body
 Calculation determined organ doses for significantly
exposed organs and sumed them to calculate EDE
 Results in EDE conversion factors in urem/hr per
uCi
Organ Dose Conversion Factors
(Sv/photon) for Selected Organs
Conservatism Applied
 Calculations do not take into consideration
reductions due to vial shield
 Due to the complex line geometry, the
highest EDE conversion factor for all 74 body
locations was selected
 The calculations assumed the line was
completely full with fluid during entire transfer
0.00E+00
Arm Bones
Scapulae
U. Rib Cage
U.I. Chest
Ribs
Outer Trunk Tissue
Bone Surface
Lungs
Clavicles
VU Torso
Breast
Esophagus
Thymus
Heart
Red Marrow
Muscle
Spine
Thyroid
Skin
Head and Neck Tissue
Spleen
Adrenals
Pancreas
Stomach
Skull
L. Rib Cage
M.I. Chest
Brain
Liver
Kidneys
Gall Bladder
T. Colon
S. Intestine
Upper Large Intestine
D. Colon
Colon
A. Colon
Lower Large Intestine
Pelvis
L. Trunk
Uterus
Gonads
U. Bladder
S. Colon
Male Genitalia
Testes
Legs
Leg Bones
Organ Doses
Total Organ Dose, mrem
3.50E+03
3.00E+03
2.50E+03
2.00E+03
1.50E+03
1.00E+03
5.00E+02
The Result
Skin Dose Calculations
 Conservatively
modeled using
Microshield.
 10 concentric rings
considered for 10
square centimeter
calculation
 Vial assumed to be
against the upper
arm
10
9
8
7
6
5
4
3
2
1
Conservatism Applied to Skin
Dose
 No consideration was given to the attenuation
or distance afforded by clothing worn.
 Method assumes that the entire 10 square
centimeters of skin was in contact with the
source during the entire exposure period,
 No adjustments were made to account for
curvature of the cylindrical source which
would have added considerable distance to
portions of the 10 square centimeter skin
area.
Shallow Dose to Ring Segments
Ring
Number
Center Radius
(cm)
Area of
Inner Circle
(cm2)
Area of
Outer
Circle
(cm2)
Area of
Ring
(cm2)
Max Dose Rate
(mrem/hr)
Contribution to
10 cm2 Dose
Rate (mrem/hr)
Contribution
to 10 cm2
Dose (mrem)
1
0.089
0.000
0.100
0.100
1.083E+06
1.080E+04
3.602E+02
2
0.267
0.100
0.400
0.300
1.067E+06
3.199E+04
1.066E+03
3
0.446
0.400
0.899
0.500
1.038E+06
5.188E+04
1.729E+03
4
0.624
0.899
1.599
0.700
9.974E+05
6.979E+04
2.326E+03
5
0.803
1.599
2.499
0.900
9.456E+05
8.508E+04
2.836E+03
6
0.981
2.499
3.599
1.100
8.869E+05
9.754E+04
3.251E+03
7
1.159
3.599
4.898
1.300
8.258E+05
1.073E+05
3.578E+03
8
1.338
4.898
6.398
1.500
7.625E+05
1.144E+05
3.812E+03
9
1.516
6.398
8.098
1.700
7.001E+05
1.190E+05
3.967E+03
10
1.695
8.098
9.998
1.900
6.398E+05
1.215E+05
4.052E+03
Maximum Shallow Dose
 Calculated by
weighting the dose
rate of each ring by
the area of the ring
 All rings summed
 Total maximum SDE
Calculated: 26.9 rem
DS
Di Ai


t
A
i
Conclusions
 Effective Dose Equivalent is the appropriate
dose to use under circumstances of nonuniform exposures

Results correlated with workers whole body
and finger dosimetry
 Assignment of a grossly overestimated TEDE
using DDE to the upper arm would have
significantly overestimated risk to the worker
and liability to the employer
Lessons Learned
 Everyone wants numbers – let them wait!
 Spin Control – Establish information flow to
senior management, risk management and
RSC chair through one point of contact.
 Establish a reporting procedure before
something happens.
 Let someone else “have the fun” to do the
dose assessment, and review what they do,
but don’t guide it.