Electronic Brachytherapy
Quality Assurance
Jessica Hiatt MS
ACMP, Virginia Beach, VA
May 2, 2009
Outline:
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Overview and intro to EB
Dose characteristics
Acceptance, commissioning and QA
Breast Trial
Endometrial Trial
Future directions
Electronic Brachytherapy:
• Internal radiation therapy that involves
placing a miniature x-ray source inside
the patient close to or in the tumor.
X-Ray Tube
Xoft Tube (2006)
HV Cable
X-ray Source
• Tube diameter = 2.25 mm
• Requires a cooling catheter
– Assembly diameter = 5.4
mm
• Nominal dose rate:
– 0.6 Gy/min at 3 cm in water
Source Characteristics:
Comparison of Dose Rate vs. Depth in Water for Various Sources
1.E+03
50 kV
1.E+02
50 kV MCNP5
Pd 103
I 125
Dose Rate (cGy/min)
1.E+01
Ir 192
1.E+00
1.E-01
1.E-02
1.E-03
1.E-04
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
Radius (cm)
Dose rate curve is quite similar to 192Ir over region of interest
Graph courtesy of Xoft
Intracavity APBI:
MammoSite HDR 192Ir
Xoft 50kV
Dickler et al. Brachytherapy, 2007
Axxent Controller:
Touch Screen
Display
Barcode
Reader
Controller
Pullback Arm
USB Port
Well
Chamber
SI Max 4000
Electrometer
Breast Applicator:
Balloon Inflation
Valve
Multi-lumen
Flexible Shaft
Drainage Holes
Radiation Source
Lumen
Drainage Port Valves
Vaginal Applicator Set:
• FDA clearance received in May 2008
for a set of reusable vaginal applicators
• Available in four diameters – 20, 25,
30 and 35 mm
• Each set contains four vaginal
cylinders, four source channels and a
board & clamp assembly
• Enhanced visibility with CT and
fluoroscopic imaging
Vaginal Cylinder:
EB
IB
EB for Skin:
• Applicator development of
10mm, 20mm, 35mm, 50 mm
• Stainless Steel:
• Easily sterilizable
• Applicator cone and source
channel
• Flattening filter integrated in
cone
Slide provided by Xoft
EB for Skin:
• Developed Axxent Applicator
compatible with system for typical
lesions (up to 50 mm diameter of
target area with 4 sizes)
• Circular
• Reusable
Scalp treatment
with Leipzig
applicator 10, 20,
30 mm sizes
Slide provided by Xoft
Commissioning and QA:
AAPM TG-182
Recommendations on Electronic
Brachytherapy Quality Management
Chair: Bruce Thomadsen
IntraBeam
Axxent
Clinical
Michael Ringor
Chris Stacey
Vendor/Vendor
Clinical
Frank Weigand
Gene Cardarelli
Mark Rivard
Jessica Hiatt
Randall Holt
Ben Smith
Calibration/QA
Tina Pike
Larry DeWerd
Acceptance and Commissioning:
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Well-chamber constancy
Beam stability
Source positional accuracy
Output stability
Timer linearity
Marker/source position coincidence
Controller functionality/safety interlocks
Treatment planning data verification
Well-chamber Constancy:
• Intercomparison - Well-chamber/Electrometer
– SI HDR Plus Well Chamber
– SI Max 4000 electrometer
– 4 mg Ra-eq Cs-137 source
Well Chamber Constancy Check
RIH Unit
Readings (pA)
41.928
41.892
41.885
Percent
Difference:
-1.89
41.944
41.967
41.976
Percent
Difference
-0.73
Xoft Unit
Readings (pA)
Beam Stability:
• Simulated treatment data extracted from
controller and plotted.
Source Positional Accuracy :
QA Test Fixture
Digitized image of film positioned w/in fixture
during exposure
Output Stability :
Source Stability Measurements
Rate (nA)
Trial Number
Dwell
Position
(cm)
1
2
3
4
5
Ave.
SD
Rel.
SD
24.5
0.006
0.006
0.006
0.006
0.006
0.006
0.000
0.00
23.5
0.022
0.022
0.022
0.022
0.022
0.022
0.000
0.00
22.5
0.110
0.112
0.111
0.111
0.111
0.111
0.001
0.01
21.5
0.190
0.199
0.199
0.200
0.199
0.197
0.004
0.02
20.5
0.077
0.079
0.080
0.080
0.080
0.079
0.001
0.02
Total Rate
(nA)
0.405
0.418
0.418
0.418
0.418
0.416
0.006
0.01
Timer Linearity:
Marker/Source Position
Coincidence:
Controller Functionality and
Safety Interlocks:
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Setup and delivery
Status indicator light
Emergency-off
Treatment recovery
Applicator symmetry
Pullback force error
No travel through bent applicator
Treatment Planning Data
Verification:
Jessica Hiatt
Daily QA:
Daily QA:
Pre-treatment
checklist:
Monthly QA:
EB QA Conclusion:
• EB offers the potential
to profoundly impact
brachytherapy practice
• As of this moment,
institutions need to form
their own QA
procedures
• AAPM TG-182 will
brainstorm
recommendations for
EB QA