Background. Radiation protection of patients undergoing radiation therapy using linear electron accelerators is based on ensuring the constancy of the equipment parameters set during commissioning. Therefore, studying the possibility of operational assessment of the spectrum characteristics consistency of the generated bremsstrahlung is a priority along with standard dosimetric parameter control procedures. Primarily, this refers to specifying the average measured energy of bremsstrahlung which provides an impartial assessment of the constancy of the whole wave path of the accelerator. However, there is no special diagnostic equipment to determine this parameter. At the same time, the literature data represent a growing interest in the use of CdTe sensors for the analysis of high-energy radiation, including the ones in medical accelerators. Purpose – developing and testing special diagnostic equipment based on semiconductor CdTe sensors, which would implement the assessment of the average measured energy of bremsstrahlung of the medical accelerator 6 MeV via comparing the mass attenuation coefficients in lead and aluminum. Materials and Methods. The paper deals with experimental evaluation of the Varian Clinac 600C linear accelerator (USA) spectrum characteristics carried out at Radiation Oncology Department of State Organization «Grigoriev Institute for Medical Radiology and Oncology of the National Academy of Medical Sciences of Ukraine» via determining the average measured energy of bremsstrahlung. The assessment of the average measured energy of the bremsstrahlung of the accelerator was performed based on comparing two mass attenuation coefficients of radiation with materials having significantly different atomic numbers, i.e. Al and Pb. The assessment of the mass attenuation coefficients was performed on the basis of measuring the average amplitudes of CdTe signals of the sensor, operating in the pulse mode in conjunction with a 16-bit ADC. Pulses of bremsstrahlung from the linear accelerator were recorded by a peak detector for 10 seconds of measurement by the hardware-software complex at 400 monitor units by CdTe sensor with aluminum and lead absorber. The study was performed at a distance of «source-surface» 100 cm with an area of the irradiation field of 20x20 cm. The spectral energy profile of the generated field of bremsstrahlung was studied. Results. The developed equipment was tested by CdTe sensor, which was created taking into account the energy sensitivity of the sensor itself as well as the spectraltemporal characteristics of the pulsed radiation of the accelerator. The approach dealing with assessing the average measured energy of bremsstrahlung of the linear electron accelerator, based on the dependence of the attenuation of radiation by the absorber layer on the radiation energy, has been experimentally confirmed. The theoretical dependence of the average measured energy of bremsstrahlung of the linear accelerator on the ratio of the mass attenuation coefficients of lead and aluminum has been obtained. The energy range from 0.1 to 6 MeV corresponds to the ratio of mass absorption coefficients of lead to aluminum, varying nonlinearly from 33.8 to 1.639. The average measured energy of the linear accelerator of 0.8 MeV corresponds to a mass coefficient ratio of about 1.23 for these materials. The assessed absolute error (from the set value during commissioning the linear accelerator) of the specified measured average energy of bremsstrahlung is up to 12.5% (0.72 MeV), corresponding to the ratio of mass attenuation coefficients – 1.340. Conclusions. The special diagnostic equipment for recording the spectrum characteristics of the Varian Clinac 600C linear accelerator (USA) based on semiconductor CdTe sensors, which along with 16-bit ADC make it possible to estimate the average measured energy of bremsstrahlung via comparing mass attenuation coefficients in Al and Pb has been substantiated and reduced to practice. The assessment of mass attenuation coefficients is carried out based on measuring the average amplitudes of pulses of СdTe sensors operating in a pulse mode.

Background. Radiation therapy is an essential in the complex of modern cancer care methods, since it is needed by more than half of cancer patients worldwide. However, each year more than 2 million people from low-income countries are unable to access modern radiotherapy technologies [1]. Thus, the urgent task in the field of radiation oncology is to increase the availability, quality and efficiency of radiotherapy, monitoring the level of technical, methodological and human resourcing of radiation therapy in Ukraine in accordance with trends in Europe and the world. The actual task of the study is to review and analyze the existing level, availability and effectiveness of applying the modern technologies of radiation therapy in the regions of Ukraine. Purpose – analyzing the current state and level of availability of radiotherapy in Ukraine, seeking for opportunities to expand applying it. Materials and methods. Analyzing and comparing statistical data of the National Cancer Registry of Ukraine and the information of IARC GLOBOCAN, IAEA DIRAC Database, summarizing the results. Results. The level of technical and technological equipment as well as staffing of oncology centers of Ukraine has been analyzed, along with assessing quantitative and qualitative components of radiotherapy care in comparison with the average European indicators. The assessment of the state of radiotherapy care in Ukraine was carried out with due regard for the increasing number of patients. Conclusions. According to the WHO, the structure of cancer incidence in Ukraine is similar to the European one, however higher specific mortality rate indicates, first of all, the insufficient level of covering the population of Ukraine by specialized diagnosis and oncological care, its low efficiency and engineering backwardness. It has been determined that radiation therapy in Ukraine is needed annually by at least 90 thousand cancer patients. In fact, only about 44 thousand of them are provided with tele-radiation therapy. First of all, this is due to extremely insufficient radiotherapy equipment available in Ukraine and using outdated radiation treatment technologies in gamma-ray teletherapy that result in its low quality and aggravating the clinical consequences. Given the growing number of cancer patients in 2022, Ukraine will need about 160 machines for tele-radiotherapy. The rise and adjusting the clinical and technical capabilities of regional oncology centers in terms of quality and efficiency of radiation therapy is possible under the conditions of their rapid technical.

The problem of cancer incidence in Ukraine in the socio-demographic aspect in comparison with the data of the Western European region is considered. The role of radiation technologies in the system of oncological care to the population of Ukraine, their technological level and clinical efficiency are analyzed. The main directions of increasing the possibilities of the branch of radiation therapy in Ukraine with the involvement of mechanisms of national planning and coordination of the modernization process are offered. The availability of the latest technologies of radiation therapy will not only improve the quality of cancer care in Ukraine, but also increase the potential of research and raise the professional level of staff of cancer centers. Key words: radiation oncology, radiation therapy, linear accelerator of electrons, radiation treatment modalities