1. Xoft Manufacturing Procedures
Every
Source
Tested
Thoroughly

2. Xoft Tests Every Source we Build
Testing of an isotope seed typically consists simply of a measurement of the output level
Spatial characteristics are just as important to accurate treatment as the overall output
Xoft sources are tested for output, polar and azimuthal distributions, depth dose and dose rate constant
Being electronic sources, they are also tested for several stability related parameters

3. Xoft Manufacturing Test Fixture
From an AAPM 2008 oral presentation
A high precision, high throughput fixture for routine spatial characterization of the Xoft Axxent™ miniature x-ray source
Describes the custom built device which tests every Xoft source
Polar distribution
Azimuthal symmetry
Depth dose
Dose rate constant

4. Manufacturing Test Fixture (MTF) Design
Source
Water tank phantom
Shielded enclosure with leaded acrylic window
Carousel assembly holding all detectors
Shielded bridge and diode amplifiers on top plate
Source to be tested is fixed, carousel assembly rotates
Bridge Assembly
Top Plate (raised)
Carousel Assembly
Acrylic water tank
Leaded acrylic and stainless steel enclosure
Carousel assembly with all detectors
PTW ion chamber
Hamamatsu S8559 Scintillator/photodiodes
critical fixtures are Solid WaterTM
Source to be tested is fixed, carousel assembly rotates
Shielded bridge on top plate with diode amplifiers
Water Tank Assembly

5. MTF Carousel Plate 1 cm miniature x-ray ion chamber
2 cm C-arm: 6 photodiode detectors
Cross-calibrated to ion chamber
7cm detector
1 cm Ion chamber
C-arm detectors
C-arm measures polar distribution
Carousel rotates around source
Detector at various distances measure depth dose
4cm detector
1cm: miniature soft x-ray ionization chamber
used to measure depth dose
can be moved to all other diode distances to calibrate the photodiode detectors
2cm C arm photodiode detectors: 0°,30°,60°,90°,120°,150°.
Hamamatsu S8559 x-ray monitor detector
designed for x-ray detection below 100keV
5.8mm diameter
CsI scintillator
custom gain amplifiers for the different distance detectors
calibrated in place with the IC
measures the polar distribution at 0,30,60,90,120,150 degrees
90 deg – measures the azimuthal deviation
90deg – measures depth dose
4 and 7 cm photodiodes
measure depth dose
Source holder
fixed stop for positioning the source anode
Tolerances .002 in
enclosures measured at a metrology house or at xoft
custom made gauges for in situ measurements
actual detector positions entered into software
90°: azimuthal and 2cm depth dose
4cm and 7cm photodiodes: depth dose
Position tolerances: .002” - measured and software corrected
Alignment assembly
Source to test
Carousel plate

6. MTF Creates a Wealth of Data for Each Source
Deviation from TG43 reference
Depth dose readings
One of a total of 6 sheets describing the spatial parameters and test conditions
Go into the record for each accepted source
Sample Printed Output – Depth Dose

7. High Precision Measurements
Performance qualification: repeatability, reproducibility, operator to operator variability
Operator to operator variability was measured to be less than 1% for 3 operators testing 3 sources during performance qualification
Performance qualification
repeatability – one source tested 5 times without removing it from the fixture
reproducability – one source tested 5 times removing it each time from the fixture
operator to operator variability – 3 operators testing 3 sources
Azimuthal deviation from average
Polar distribution (avg over all azim angles)

8. Spatial Plots for 25 Sources Show Low Variability
Normalized depth dose distributions averaged over azimuthal angle
Azimuthal asymmetry as percent deviation from the average.
Normalized polar output averaged over azimuthal angle. 0° is along the source axis.

9. Output Level and Stability
From an AAPM 2007 Poster
Xoft Routine Per Article Manufacturing Testing of the Axxent® Source
Source is cycled 10 times
Last cycle held for 20 minutes
Data analyzed for peak reproducibility, noise and drift

10. Xoft’s Policy Every source is tested
To ensure that every treatment is safe and accurate