Experience from long-term monitoring of RAKR ratios in (192)Ir brachytherapy.
BACKGROUND
Ratios of values of brachytherapy source strengths, as measured by hospitals and vendors, comprise constant differences as, e.g., systematic errors in ion chamber calibration factors and measurement setup. Such ratios therefore have the potential to reveal the systematic changes in routines or calibration services at either the hospital or the vendor laboratory, which could otherwise be hidden by the uncertainty in the source strength values.


METHODS
The RAKR of each new source in 13 afterloading units at five hospitals were measured by well-type ion chambers and compared to values for the same source stated on vendor certificates.


RESULTS
Differences from unity in the ratios of RAKR values determined by hospitals and vendors are most often small and stable around their mean values to within +/- 1.5%. Larger deviations are rare but occur. A decreasing ratio, seen at two hospitals for the same source, was useful in detecting an erroneous pressure gauge at the vendor's site.


CONCLUSIONS
Establishing a mean ratio of RAKR values, as measured at the hospital and supplied on the vendor certificate, and monitoring this as a function of time are an easy way for the early detection of problems with equipment or routines at either the hospital or the vendor site.
Carlsson Tedgren
Asa
A
Radiation Physics, Department of Medical and Health Sciences (IMH), Linköping University, Linköping, Sweden. asa.carlsson-tedgren@imv.liu.se
Bengtsson
Emil
E
Hedtjärn
Håkan
H
Johansson
Asa
A
Karlsson
Leif
L
Lamm
Inger-Lena
IL
Lundell
Marie
M
Mejaddem
Younes
Y
Munck Af Rosenschöld
Per
P
Nilsson
Josef
J
Wieslander
Elinore
E
Wolke
Jeanette
J
D001918:Brachytherapy / Q000295:instrumentation*; D002138:Calibration; D006801:Humans; D007496:Iridium Radioisotopes / Q000627:therapeutic use*; D011874:Radiometry / Q000295:instrumentation*; D011879:Radiotherapy Dosage
D007496:Iridium Radioisotopes