Local absorbed doses of irradiation of medical personnel at brachytherapy of prostate cancer using 125I microsources of Russian production

Brachytherapy with microsources of 125I is effective and minimally invasive method of radiation therapy of prostate cancer. At present moment the "State National Center of Russian Federation - Physical-Energetic Institute named after A.I. Leipunskiy" (Obninsk) is producing 125I microsources for treatment of prostate cancer. The Medical Radiological Research Center named after A.F. Tsyb (MRRC, Obninsk) is responsible for clinical trials of these radioactive sources. In connection with these circumstances it is necessary to obtain information about local radiation doses of personnel - irradiation the skin of the fingers and eyes of radiation oncologist and medical physicist, performing necessary procedures at the stages of preparation and conduction of the operation with 125I microsources of Russian production. Results of such dosimetry are very important for wide dissemination and implementation of 125I microsources of Russian production in the radiological clinics. Due to low energy of photon irradiation, as well as due to features of the preparatory procedures and the operation itself, fingers and eyes of medical staff may be the most irradiated locations of the body during the brachytherapy of prostate cancer with 125I sources. The radionuclide 125I decays by electron capture mode with a half-life of 60.2 d, emits characteristic photon radiation (average energy of 28.33 keV, the layer of half attenuation in soft tissue is about 2 cm), electrons of internal conversion and Auger-electrons (these electrons are completely absorbed in the material of the sealed capsule of source). When measuring the absorbed doses from low-energy radiation quanta, the main problem is the validity of measurement results, because the dosimeters must be sensitive enough in the range of low energies and the energy dependence of their response must be known. For dosimetry of irradiation from 125I microsources during brachytherapy the miniature crystals of aluminum oxide (α-Al2O3:C) were used as thermoluminescent (TL) dosimeters of low energy quantum radiation. The intensity of thermo stimulated luminescence emitted by crystals of aluminum oxide is proportional to radiation dose. The “Harshaw 3500” TL reader was used for measurements of thermo stimulated luminescence. The dosimeters were placed in light-tight envelops. The three dosimeters were placed in the conditions of electronic equilibrium in each opaque envelop. The area of each set of dosimeters is equal to 2.7 cm2, the thickness of the covering layers of dosimeters is equal to 40 mg/cm2 (for the skin of hands) and 300 mg/cm2 for eyes (in accordance with the terms of the Russian Radiation Safety Standards RSS-99/2009). Dosimeters were placed on the all fingers of both hands of medical personnel, as well as near eyes of radiation oncologist. At average energy of 125I quantum irradiation (28.33 keV) the aluminum oxide dosimeters provides increased values of doses - value of factor of overestimation of dose in relation to the dose from irradiation by high energy gammas is equal to 2.84±0.04. Therefore the measured values of absorbed doses have been reduced by the value of this factor. It was shown that under standard conditions of brachytherapy of prostate cancer, the local absorbed doses of radiation oncologist are equal to 0.18±0,019 mGy (in the skin of index finger of the left hand - the highest dose) and 0.053±0.0057 mGy (in the skin of little finger of the right hand - the smallest dose). The absorbed doses in right and left eyes, are equal to 0.11±0,012 mGy and 0.035±0.0039 mGy, respectively. Local absorbed doses of medical physicist are equal to 0.16±0,034 mGy (in the skin of index finger of the left hand - the highest dose) and 0.013±0.0012 mGy (in the skin of ring finger of the right hand - the lowest dose). The background dose was taken into account when analyzing the r