Influence of the non-homogeneity of Ir-192 wires in calibration of well chambers.
All international recommendations point out as necessary the calibration or verification of the reference air kerma rate (RAKR) for brachytherapy sources (independent of manufacturer established value) prior to their clinical use. The most common procedure for RAKR measurement in iridium wires is based on the use of well chambers with specific inserts that set the wire in a fixed position; previously, the electrometer plus well chamber with insert (EWI) was calibrated by using a source obtained from an accredited laboratory for which the RKAR was established precisely, called the 'reference' source. The distribution of Ir-192 material in the wire could be not perfectly homogeneous all along its length, and in this case the influence of these inhomogeneities in the calibration process should be studied. This paper focuses on the evaluation of this topic and an analytical and experimental study is presented taking into account the non-homogeneity of Ir-192 material along the wire for both the reference source (of length 14 cm) and a wire of unknown RAKR. This study is based on measurements with a 1 cm iridium wire on a rectilinear insert considering either of the two available reference sources (1 or 14 cm length), and has been experimentally evaluated using two typical well chambers. The main conclusion of the study is that if the non-homogeneity of the wires is lower than 5% the effect of non-homogeneity on RAKR measurements is negligible for rectilinear inserts even for short well chambers.
Pérez-Calatayud
J
J
Radiation Oncology Department, La Fe University Hospital, Valencia, Spain.
Ballester
F
F
Granero
D
D
Brosed
A
A
D000465:Algorithms; D016880:Anisotropy; D001918:Brachytherapy / Q000295:instrumentation* / Q000379:methods / Q000592:standards*; D002138:Calibration / Q000592:standards; D003198:Computer Simulation; D019544:Equipment Failure Analysis / Q000379:methods* / Q000592:standards*; D005062:European Union; D007496:Iridium Radioisotopes / Q000032:analysis* / Q000592:standards / Q000627:therapeutic use; D008962:Models, Theoretical; D011829:Radiation Dosage; D011874:Radiometry / Q000295:instrumentation* / Q000379:methods / Q000592:standards*; D011879:Radiotherapy Dosage; D012015:Reference Standards; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
D007496:Iridium Radioisotopes