Zeiss INTRABEAM, Instructions For Use Manual

Page: 51 / 82

Version 6.2
G-30-1767-en
Page 51
INTRABEAM Water Phantom Operation
Important information on dose rate values
The following information on dose rate values refers to the measuring method
"Measured according to TARGIT" and the method "Calibration v4.0" (for the
INTRABEAM Water Phantom, among others).
The INTRABEAM system with its characteristic low-energy X-ray therapy and
the challenge to dosimetry associated with it has existed since 1990. With the
development of a water phantom used expressly for measuring the low-en-
ergy X-ray source of the INTRABEAM system, an additional quality assurance
accessory is now being offered to the customer. At the same time, a customer
request for a required measurement setup for precise positioning of the X-ray
source in relation to the PTW 34013 ionization chamber has been met by in-
troducing a smaller entrance window. Likewise, a justified customer request
to adapt the algorithm for calculating the water energy dose to international
standards (AAPM TG61 and IAEA TRS 398) also has been implemented. Both
of these requests were discussed and implemented in close cooperation with
the TARGIT Physics Group, which is internationally staffed by qualified physi-
cists.
TARGIT measuring method
This measuring method is based on the use of a PTW TN23342 ionization
chamber calibrated by means of a standard ion dose. This chamber is located
in a specially designed watertight holder, which is mounted inside a gold
standard water phantom. A roentgen to gray conversion factor of 8.81mGy/
R (taken from ICRU Report No. 17) is used to convert the measured standard
ion dose to a water energy dose.
Calibration v4.0 measuring method
This process is thoroughly described in the present Instructions for Use (for the
INTRABEAM Water Phantom). The measuring method is based on the use of
an air-kerma calibrated PTW TN34013 ionization chamber. This ionization
chamber is located in a specially designed watertight holder which is mounted
inside a gold standard water phantom. In order to convert the measured air
kerma value to a water energy dose, a
conversion factor is used
which is in each case determined by the manufacturer of the ionization
chamber (PTW) during the calibration of the ionization chamber there.
K
Ka D
W