Quality Assurance Tests for Prostate Brachytherapy Ultrasound Systems

what task group covers Quality Assurance Tests for Prostate Brachytherapy Ultrasound Systems

TG-128

list the 8 tests recommended for annual US QA

• grayscale display accuracy

• depth of penetration

• axial/sagittal resolution

• axial/sag distance scales

• cross sectional area accuracy

• volumetric accuracy

• needle and grid alignment

• tx planning computer volumetric accuracy

Grayscale display accuracy

1. Checks that the monitor used to display the ultrasound images is performing accurately (i.e. that the monitor is adjusted for optimal visibility).

   Calibration and brightness can drift as a function of time.

   Phosphors with the monitor can fade over time.

2. Uses built in scale (either steps or gradient) ranging from black to white.

3. Examine the scale and see where you can no longer see a difference in the scale:

   For steps, this should be within two steps of your baseline value.

   For a gradient, the distance between the brightest and darkest visualized point should be within 10% of baseline.

depth of penetration test

1. Note: dead transducer elements will result in a reduction in the depth of penetration.  Also, an increase in the system’s noise will reduce the depth of penetration.

2. Examine the point in the phantom where the static speckle pattern gives way to dynamic electronic noise.

3. Or, if there are low contrast discs, measure the depth at which they can no longer be visualized.

4. The maximum depth of penetration should be within 1 cm of baseline.

resolutions test

1. Measure the dimensions of monofilaments (wires) in the axial plane in both the near zone (1-2 cm) and the far zone (5-6 cm).

2. Should be within 1 mm of baseline.

distance scales test

1. Measure the distance in between monofilaments separated by known distances (both near and far zone).

2. Should be within 2 mm or 2%, whichever is larger for axial

3. Should be within 3mm or 3% whichever is larger for sagital

cross sectional area accuracy

1. In axial mode, measure the area of a cross sectional area of a known object.

2. Should be within 5%.

volumetric accuracy

1. In axial mode, measure the volume of a known object (preferably of prostate size 20-30 cc).

2. Should be within 5%.

Needle and grid alignment

1. Using either a bucket of water or phantom attach the grid and insert a needle.

2. Ensure that needles align with the grid on the ultrasound unit within 3 mm.

3. If using a water bucket, the speed of sound in water is only 1480 m/s (compare to 1540 m/s in tissue), introducing distance errors:

1. Raise temperature to 48 ^oC.

2. Increase salinity to 45 parts per thousand (about 6 tbsp per liter).

treatment planning computer volumetric accuracy

1. Export images of a known volume to the treatment planning computer.

2. Contour and measure the volume.

3. Should be within 5%.