Intracavitary "in vivo" dosimetry at the high dose rate brachytherapy in oncogynecology

The technology for construction and application of flexible dosimetric assemblies with LiF:Mg,Ti microcrystals (sizes of about 0.1 mm) for off-line measurements of the spatial distribution of the absorbed dose inside organs at risk (rectum, urethra, vagina) at high dose rate brachytherapy in oncoginecology has been developed. The transfer from the usage of luminescent dosimeters LiF:Mg,Ti with macro sizes (more than 1 mm) to microdosimetrs with sizes of about 0.1 mm, in combination with the developed protocols of dose estimations using mini-aliquots (10 mg) of luminescent microdosimeters, provided possibility to increase the accuracy of dose measurements in the therapeutic dose range at high dose rate brachytherapy of gynecological malignancies. The developed technology of intracavitary dosimetry at a high dose rate brachytherapy (129Ir source) in oncogynecology was tested in the clinic (25 patients). It was found that, as a rule, the measured doses were in a good agreement with the calculated doses in the areas of interest. However, in four cases (16% of all patients) there was an excess of the measured local absorbed doses over the calculated ones (from 0.6 to 1 Gy) in the urethra and rectum (in the organs of maximum calculated doses). These cases may be considered as a basis for monitoring of the patients’ condition in the post-therapeutic period. However, the values of maximal dose were within acceptable dose range, as recommended by GEC-ESTRO. The developed technology of «in vivo» dosimetry allows to adjust the dosimetrical plans at multifractional high dose rate brachytherapy. The results of clinical approbation of the developed technology of «in vivo» dosimetry show the importance of this technology as an essential element of dosimetric assurance of the quality of high dose rate brachytherapy in oncogynecology.