Iridium-192 Radiotherapy Benefits in the Management of Gynecological Tumors

Abstract

Background. Application of the most advanced radiation technologies of brachytherapy featuring the high dose rate sources i.e. 60Co and 192Ir within contemporary management protocols for gynecological cancer provides maximum dose distribution in the clinical target along with minimal radiation exposure on surrounding organs and tissues. It involves irradiation of large spaces with delivery of high therapeutic doses at the tolerance bound of «critical» organs (bladder, rectum) and tissues. Thus minimization of the early and late radiation complications, life span extent and quality of life increase remain just the issues in contemporary radiation oncology requiring therefore the elaboration of radiobiological criteria along with substantiation of physiсо-engineering properties of the radiation sources. Taking into account the basic radiobiological patterns will ensure a definitive further progress in the field of radiation oncology. Objective: to study and compare the biological effects of 192Ir with the effects of the reference gamma radiation 60Co and increase the effectiveness of brachytherapy using a 192Ir source. Materials and methods. Radiobiological dosimetry on the basis of a test system of peripheral blood lymphocytes from the gynecological cancer patients with subsequent cytogenetic analysis of radiation-induced chromosome aberrations was performed to study and compare the biological effects of 192Ir and reference 60Со γ-radiation, and to enhance the efficiency of 192Ir brachytherapy. Results. Radiation markers, i.e. dicentric chromosomes with an accompanying paired fragment prevailed in the spectrum of radiation-induced damage. Variability of individual cytogenetic parameters of peripheral lymphocytes upon the first fraction of irradiation at the same dose of 5 Gy indicated an individual sensitivity of patients to the 192Ir γ-irradiation. Comprehensive conservative treatment with adjuvant radiotherapy was applied to the patients (n = 98) having got secondary vaginal cancer stage II–III, T2-3N0-1M0. The high dose-rate (HDR) brachytherapy using 192Ir radiation sources was applied in the main study group (n = 37), HDR brachytherapy using 60Co radiation sources was applied in the control group (n = 35). Conclusion. The HDR brachytherapy with 192Ir and 60Co sources on the up-to-date technology intensive devices provides a high accuracy of dose distributions when irradiating the malignant neoplasms with minimized radiation exposure to the «critical» tissues. Treatment results are improved therefore. The use of 192Ir radiation sources compared with 60Co ones resulted in an increased throughput of treatment, enhanced tumor regression, and reduced incidence of radiation effects on the critical organs. Currently we perform the radiobiological studies on somatic cells from cancer patients at the genetic, biochemical, biophysical, and cytological levels in order to receive a biological indication of radiation damage under the impact of 192Ir isotope. Continuation of clinical trials with radiobiological support will provide an opportunity to predict the early and late radiation complications and thus to provide a personalized approach in brachytherapy of cancer patients using the 192Ir sources of γ-rays. Key words: HDR brachytherapy, 192Ir and 60Co high dose rate sources.