what is TG 128?
QA for prostate US brachy systems
items tested in TG28
grayscale visibility
depth of penetration
axial and lateral spatial resolution
axial and lateral distance measurement accuracy
Area and volume measurement accuracy in both the US system and the TPS
template and electronic grid alignment (on both the US screen and on the TPS screen)
frequencies for which you perform TG128 tests
all available frequencies
both axial and longitudinal US arrays
speed of sound software assumes
1540 m/s
phantom must mimic this speed
elements required in US phantom
- a high contrast egg-shaped volume object
- A series of midcontrast detail objects for depth of penetration measurements
- An array of high contrast targets for verification of electronic grid [?]
- An array of high contrast targets in all 3 orthogonal directions for spatial accuracy verification
- An array of small reflectors for spatial resolution evaluation in 2 orthogonal directions, near surface and at some depth. [3, 4 and 5] may be combined.
- Some way of testing the alignment of the physical needle template with the electronic grid (can check this by placing needles in the grid and making sure they show up at the correct location)
Phantom geometry may change over time due to aging of materials
action level: grayscale visibility
annual
change > 2 steps or 10 % from baseline
depth of penetration action level
annuak
change > 1 cm from baseline
axial and lateral resolution action level
annual, change > 1 mm from baseline
action level: axial distance measurement accuracy
annual, error > 2 mm or 2 %
action level: lateral distance measurement accuracy
annual, error > 3 mm or 3 %
action level: area measurement accuracy
annual
error > 5 %
action level: volume measurement accuracy
annual
error > 5 %
action level: needle template alignment
annual
error > 3 mm
treatment planning computer volume accuracy
acceptance testing
error > 5 %
