In vivo dosimetry at high dose rate brachytherpapy for prostate cancer using 192Ir: comparison of dose distribution between planned and measured doses with intracavitary placement of autonomous luminescence microdosimeters

We present results of comparative study of the distributions between planned and measured doses with intracavitary placement of autonomous luminescence microdosimeters in the process of high-dose rate brachytherapy for prostate cancer using 192Ir. The results were obtained with the use of technology consisting in the application of autonomous luminescence microdosimeters, which were distributed in the depth in the region of the urethra and the rectal region with the purpose of verification of gradients of the calculated (planned) doses. Microdosimeters in the form of a powder of microcrystals of LiF (size about 150 µm) were hermetically packed inside a flexible tissue-equivalent tubes to ensure electronic equilibrium, and then placed inside medical catheters. Measurements of radiation-induced signals in microdosimeters were performed by the method of thermally stimulated luminescence (TL). Absorbed doses were determined using the dose calibration dependencies for microdosimeters with the use of standard sources of ionizing radiation. Medical catheters were introduced in accordance with technology for high dose rate brachytherapy. Instrumental measurement of the distribution of measured doses was performed for 30 patients. Comparison of measured doses with calculated (planned) dose data shows that in the urethra, near the tumor, the measured doses agree well with the calculated ones (differences do not exceed 5%). Meanwhile, the calculated dose in the distal (rectal) region differ significantly from the calculated ones. The improvements of such kind of “in vivo” dosimetry technology is in a process.