Manifestations of late radiation urethritis in comparison with instrumental assessments of the spatial intra-cavity distribution of doses in the organ after high dose rate brachytherapy of prostate cancer with the use of 192Ir: preliminary results

The technology of instrumental ( in vivo ) measurements of spatial intra-cavity distribution of absorbed dose in the urethra and rectum using autonomous luminescent microdosimeters was developed and applied in A. Tsyb MRRC as a part of the quality assurance program of high dose rate brachytherapy for prostate cancer using 192Ir source and in order to take adequate measures after radiotherapy regarding possible complications of irradiation. At the end of 2018 in vivo measurements of the spatial distribution of absorbed doses in the urethra and rectum were performed among 50 patients (30 of them in 2017). During first year after radiotherapy there were no complaints from patients that are specific for radiation complications. A year after brachytherapy, an active survey of 30 patients cured in 2017 was conducted regarding complaints related to the urethra and rectum. In relation to rectum no complaints were presented. Six of these 30 patients presented complaints regarding urethra. These complaints (at the time of the survey) can be interpreted as manifestations of late radiation urethritis. The results of in vivo measurements of the spatial distribution of absorbed doses show that the values of the measured doses are in good agreement with the results of the planned (calculated) doses in the urethra and rectum in those patients who have not presented complaints. Meanwhile, in six patients (among 30 patients who underwent brachytherapy, and who presented complaints about the urethra a year after radiotherapy), the significant excesses of the measured doses compared with the planned (calculated) dose were estimated. For these six patients, the maximum values of the measured absorbed doses in the urethra (prostatic part of urethra) are ranged from 18 to 25 Gy (from patient to patient) with a measurement's accuracy of 5%. The measured maximum absorbed doses in rádix pénis, where the estimated (planned) doses are not available, are ranged from 3 to 6 Gy with a measurement's accuracy of 5%.