In vivo dosimetry in the urethra using alanine/ESR during Ir-192 HDR brachytherapy of prostate cancer-a phantom study

A phantom study for dosimetry in the urethra using alanine/ESR during Ir-192 HDR brachytherapy of prostate cancer is presented. The measurement method of the secondary standard of the Physikalisch-Technische Bundesanstalt had to be slightly modified in order to be able to measure inside a Foley catheter. The absorbed dose to water response of the alanine dosimetry system to 192Ir was determined with a reproducibility of 1.8% relative to Co-60. The resulting uncertainty for measurements inside the urethra was estimated to be 3.6%, excluding the uncertainty of the dose rate constant Lambda. The applied dose calculated by a treatment planning system is compared to the measured dose for a small series of Ir-192 HDR irradiations in a gel phantom. The differences between the measured and applied dose are well within the limits of uncertainty. Therefore, the method is considered to be suitable for measurements in vivo.