Thermoluminescence Sensitization of Phyllite Natural Rock

A sensitization procedure is used to enhance the thermoluminescence (TL) sensitivity of phyllite to emit radiation. Phyllite is a type of foliated metamorphic rock made from slate. This study examines naturally grown phyllite rock, which had not been previously studied. Using a Thermo 3500 manual reader, the TL sensitivity of phyllite as a function of dosage was measured. The doses required to perform this study were administered using a 60Co source. The statistical regression test of the data had a significance level of p < 0.05. The study also included thermal and pre-dose effects. Using the sensitization procedure, the nonlinearity in TL dose–response was removed, and the sensitivity was increased 44 times that of its original value. The fading study showed a dependence on the test dose. According to the obtained results, the combination of linear dose–response and high sensitivity to gamma radiation makes phyllite an important rock for dating and retrospective dosimetry.

Heart atlas for retrospective cardiac dosimetry: a multi-institutional study on interobserver contouring variations and their dosimetric impact

Purpose Cardiac effects after breast cancer radiation therapy potentially affect more patients as survival improves. The heart’s heterogeneous radiation exposure and composition of functional structures call for establishing individual relationships between structure dose and specific late effects. However, valid dosimetry requires reliable contouring which is challenging for small volumes based on older, lower-quality computed tomography imaging. We developed a heart atlas for robust heart contouring in retrospective epidemiologic studies. Methods and materials The atlas defined the complete heart and geometric surrogate volumes for six cardiac structures: aortic valve, pulmonary valve, all deeper structures combined, myocardium, left anterior myocardium, and right anterior myocardium. We collected treatment planning records from 16 patients from 4 hospitals including dose calculations for 3D conformal tangential field radiation therapy for left-sided breast cancer. Six observers each contoured all patients. We assessed spatial contouring agreement and corresponding dosimetric variability. Results Contouring agreement for the complete heart was high with a mean Jaccard similarity coefficient (JSC) of 89%, a volume coefficient of variation (CV) of 5.2%, and a mean dose CV of 4.2%. The left (right) anterior myocardium had acceptable agreement with 63% (58%) JSC, 9.8% (11.5%) volume CV, and 11.9% (8.0%) mean dose CV. Dosimetric agreement for the deep structures and aortic valve was good despite higher spatial variation. Low spatial agreement for the pulmonary valve translated to poor dosimetric agreement. Conclusions For the purpose of retrospective dosimetry based on older imaging, geometric surrogate volumes for cardiac organs at risk can yield better contouring agreement than anatomical definitions, but retain limitations for small structures like the pulmonary valve.

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 ob-tained data demonstrated reliable dose-response relationship for thyroid cancer in patients with diag-nosed thyroid cancer, who were children and adolescents at the time of the accident and resided in radi-oactively contaminated areas in the Bryansk region. The dose-response relationship for diagnosed inva-sive breast cancer was found in women, resided in radioactively contaminated settlements since the acci-dent 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 leu-kaemia 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 radi-ation 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 radi-oactivity 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 modi-fied 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 recur-rent 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 de-velopment 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 vivo do-simetry 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 feasi-bility 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 radia-tion doses to patients during radiotherapy is considered.

An Attempt to Reduce the Background Free Radicals in Fingernails for Monitoring Accidental Hand Exposure of Medical Workers

While it is recognized that some medical workers could receive significantly higher radiation doses to their hands than the routinely monitored personal doses, accurate retrospective dosimetry of their hand exposure is still challenging. To solve this issue, a combination of electron spin resonance (ESR) measurement and fingernails is worth to be investigated. However, the application of fingernail ESR dosimetry requires establishing an effective protocol to eliminate the background signal (BKG) which changes due to mechanical stress and other unclear factors, so that the radiation doses would be precisely evaluated from the radiation-induced signals (RIS) only. Thus, the authors investigated possible applications of antioxidants to remove or reduce the BKG in fingernails. In the present study, the effectiveness of chemical treatment using the dithiothreitol (DTT) reducing reagent was examined in irradiated and unirradiated fingernails. Chemically and non-chemically treated fingernails were subsequently exposed to 20 Gy of 137Cs γ-rays and the time changes of the BKG and RIS were confirmed in two different storage conditions: vacuum chamber and freezer. The results show that the non-chemically treated fingernails displayed significant intra-individual variations in the peak-to-peak intensities of both BKG and RIS. RIS from chemically and non-chemically treated samples showed correlations after freezer storage; signals were more stable than the samples stored in the vacuum chamber. Moreover, while the BKG of non-chemically treated samples demonstrated higher levels than those chemically treated, the intra-individual variations were further reduced by the DTT treatment. Our results imply that the use of an antioxidant for hand washing of medical workers prior to starting their work could be effective in reducing the pre-existing free radicals in their fingernails. This also suggests a practical application of hand exposure monitoring using fingernails as a part of radiological emergency preparedness in occupations where radiation or radionuclides are used. Research for finding safer and easier-to-handle antioxidants is to be focused on in future studies.