Verification of absolute dose rates for intravascular brachytherapy beta sources

The absolute dose rate around beta sources for intravascular brachytherapy was measured with thin thermoluminescent (TL) dosimeters and radiochromic f ilm. The calibration of these dosimeters was performed at the dose maximum in a 6 MeV electron beam of a linear accelerator. Compared to the values gi ven by the manufacturers, higher dose rates of about 20% for Sr-90/Y-90 sou rce trains and 20 to 40% for Y-90 line sources were found. We also measured the dose rate for a planar Sr-90/Y-90 source, which was calibrated at NIST (National Institute of Standards and Technology). This source serves as a reference for the determination of the dose rates by the supplier of the Y- 90 sources. For this source we measured a 13% higher dose rate compared to the value given in the calibration report by NIST. Our observation can have important consequences for the interpretation and comparison of the dose-r elated clinical results of intravascular brachytherapy with these and other beta sources. Also the comparison of the clinical results obtained with be ta sources and gamma sources, i.e. Ir-192, depends largely on the accuracy of the absolute dosimetry of the beta sources.