Zeiss INTRABEAM, Инструкция по эксплуатации

Страница: 50 / 82

Operation INTRABEAM Water Phantom
Version 6.2
Page 50 G-30-1767-en
Calculating the dose rate
• Calculate the absorbed dose rate to water using the following formula:
You will receive a calibration certificate for every ionization chamber (IC).
•
Take the TW30 value for the current ionization chamber (IC) from this cali-
bration certification (see the section on "Calibration Results") and use this
value for the calculation of the dose rate.
NOTE If the user compares uncorrected measured values with the calibration data,
he may obtain significant deviations of the measured values.
•
Adjust the measured values using the correction calculation.
NOTE If the user calculates the depth dose curve according to a different algorithm
than the one specified by ZEISS, significant deviations from the ZEISS calibra-
tion data may occur.
•
Always use the algorithm specified by ZEISS for calculating the depth
dose curve.
Ḋ
w
(r) [Gy/min] = absorbed dose rate to water at distance r (depth dose curve)
N
k
= detector calibration factor (see the certificate)
Q(r) = measured charge Q in one minute
D = current temperature (measured)
T
0
= reference temperature (see calibration certificate of ionization
chamber)
P
0
= reference air pressure (see calibration certificate of ionization chamber)
P = current air pressure (measured)
k
Q
= beam quality correction factor (see calibration certificate). The quality
level of an XRS 4 is approximately TW30.
K
Ka
→
DW
= Correction factor for type 34013 IC ionization chamber from
PTW, for the air kerma
→
water energy dose conversion
K
Ka
→
DW
For TW30: value from the calibration certificate of the ionization
chamber (IC).