35 years after the Chernobyl NPP accident: methods of retrospective dosimetry in assessing of the consequences of large-scale uncontrolled radiation exposures, their subsequent development and application in oncoradiology (experience of A. Tsyb MRRC)

Individual retrospective dosimetry was developed at A. Tsyb Medical Radiological Research Centre (A. Tsyb MRRC) after the Chernobyl accident for assessment and analysis of radiation effects on people lived in radioactively contaminated settlements in the Kaluga and Bryansk regions. The method was also used in radiation epidemiology case-control studies within frames of international pilot projects. The obtained data demonstrated reliable dose-response relationship for thyroid cancer in patients with diagnosed thyroid cancer, who were children and adolescents at the time of the accident and resided in radioactively contaminated areas in the Bryansk region. The dose-response relationship for diagnosed invasive breast cancer was found in women, resided in radioactively contaminated settlements since the accident till the first diagnosis of cancer that was established within the period from October 2008 to February 2013. Their age at diagnosis was under 55 years. At the same time, no dose-response relationship for leukaemia was found in children under 5 years old at the time of the accident. The individual retrospective dosimetry method has been updated and used in pilot studies for verifying conservative estimates of radiation doses to the population exposed to radiation as a result of nuclear tests at the Semipalatinsk nuclear test site, as well as for verifying estimates of external radiation doses to people affected by the accident at the Fukushima Daiichi NPP. The method was also used for estimating individual doses from residual radioactivity for the survivors of the Hiroshima and Nagasaki atomic bombings. The long-term collaboration continues under bilateral International Collaboration Agreements between the National Medical Research Radiological Centre and leading research centres in the Republic of Kazakhstan and Japan. Since 2016 researchers and physicians of A. Tsyb MRRC have modified method of stimulated luminescence of natural and synthetic materials and developed innovative technology in vivo dosimetry that has been put into clinical practice for estimating spatial radiation doses distribution in internal organs at risk during the brachytherapy of prostate cancer, gynecologic and recurrent pelvic tumors, as well as for estimating local radiation dose to the skin of the breast gland with the tumor. The 35-year experience in the development and application of methods for individual retrospective dosimetry after the Chernobyl accident formed the basis for identifying future-pointing trends for the development of novel applications of stimulated luminescence techniques. Radiation-induced stimulated luminescence dosimetry can be applicable in uncontrolled radiation events; retrospective dosimetry method applicable for neutron beam radiation therapy is under development. The method of in viv o dosimetry is useful in radiation oncology. Now assembled thermoluminiscent micro-sized dosimeters are used for arterial radioembolization. At present, feasibility of using items of clothing and special inserts (buttons, fastenings, etc.), parts of wearable electronic devices as natural dosimeters, as well as the feasibility of using luminescent microdosimeters, made of different materials, after exposure to high LET radiation ranged from a fraction of mGy to the dose greater than 60 Gy have been examined. Development of flexible planar microdosimeter assemblies in order to obtain more detailed information about possible discrepancy in distribution of planned and actual radiation doses to patients during radiotherapy is considered.