5
1.5. Mammography Systems
The
kVp, dose, and HVL
should be measured in the direct beam with the internal
detector. The HVL must be measured with the built-in HVL application in the QABrowser
or in oRTIgo. For further information about how that is done, see the Piranha manuals.
Note 1
: With the internal detector, the dose values given in the QABrowser or Real-Time
meter are not corrected for the added filtration and the use of these as a basis for an
HVL calculation will give an incorrect result.
For measurements of dose after the IQST phantom use the small external dose detector
(PDP).
Note 2
: This is the only measurement in mammography where this detector is used! If
HVL is measured with the external detector, the dose values are not corrected for the
added filtration (the aluminium filters) and the result will be incorrect.
An energy correction factor has to be added manually to the measured dose value. The
factors can be seen in the table 1 on next page. Use the designated favourites.
Please verify which factor that is used in the favourite according to the info next to
table 1 below.
1.6. Mammography Dose Measurements with the IQST Phantom
The setup of this type of favourite is done by first selecting to use the external dose
probe (PDP), then select the correct beam quality (Mo/30 µm Mo) and finally enter the
correction factor as the beam correction factor (found under settings). If the correction
factor is inserted there, all dose data will be corrected. For more info, please consult the
Piranha manual.
Table 1: IQST correction factors
Radiation
Quality
Mo/30 µm Mo
+ 3 mm Al &
PMMA (IQST)
Mo/25 µm Rh
+ 3 mm Al &
PMMA (IQST)
Rh/25 µm Rh
+ 3 mm Al &
PMMA (IQST)
Tube
Voltage
(kV)
RTI Radiation Quality Code
M1e
M3e
M4e
28.0
1.113
1.070
1.025
28.5
1.099
1.056
1.019
29.0
1.085
1.042
1.012
29.5
1.070
1.028
1.006
30.0
1.056
1.028
1.000
30.5
1.042
1.028
0.994
31.0
1.028
1.014
0.988
31.5
1.014
1.014
0.978
32.0
1.000
1.000
0.969
2009-09/1.0B
Piranha Dose Probe Holder User’s Manual
Important!
The typical correction factor for the PDP when
measuring with Rh/Rh after the IQST phantom at 30 kV
is
0.71.
In the standard RTI favourite “IQST w PDP Rh/Rh 30 kV”,
this value is used.
However, if you have an individual calibration factor on
a sticker inside the Piranha storm case (placed on the
content label, see picture below), please update the
standard RTI favourite for increased accuracy. Please see
the oRTIgo or QABrowser manual for details on
updating a favourite.
To get the correction factor for any other situation,
multiply this value with the corresponding tabulated
value, as shown to the left.
Typical factor inaccuracy: <5 %
Individual factor inaccuracy: <3 %