[en] Beta emitters are widely used in treatment of various oncological diseases for a long time. Alpha emitters belong to new and perspective candidates for therapeutic use and some of them have been already introduced into clinical practise. Targeted alpha-particle therapy (TAT) is a rapidly evolving field of cancer treatment. Nevertheless, there are some severe issues that prevent TAT from being a leading modality in radionuclide therapy. The nuclear recoil effect that causes the daughter nuclei release from the original radiopharmaceuticals is a critical problem for alpha emitters. Moreover, targeting and proper dosimetry is still an issue. Therefore, we focused on the dosimetry on cellular and subcellular level with an aim to quantitatively and qualitatively compare the effect of alpha and beta emitters on living cells. For our study we used Ra-223, Sm-153 and Re-186 as a model radionuclides. All radionuclides were used in the range 0-8 kBq/mL. Studied cell lines were V79 (Chinese hamster lung fibroblasts), DU145 (human adenocarcinoma cell line) and U87 (human primary glioblastoma cell line) obtained from American Type Culture Collection (ATCC). All cells were cultivated in humidified atmosphere under standard culture conditions (37℃, 5 % CO2). Chines hamster cell line (V79) was cultivated in Dulbecco’s Modified Eagle’s Medium (Sigma-Aldrich, Germany) supplemented with 10% of Fetal Bovine Serum South America Origin (Biosera, France) and 1% of Penicillin-Streptomycin (Biosera, France)). Human adenocarcinoma cell line (DU145) and human glioblastoma cell line (U87) were cultivated in Eagle’s minimum essential medium (Sigma- Aldrich, Germany) supplemented with 10% of Fetal Bovine Serum of South America Origin (Biosera, France), 1 % of Penicillin-Streptomycin (Biosera, France)), 1 % of L-glutamine (Sigma-Aldrich, Germany), 1 % of Nonessential amino acids (Sigma-Aldrich, Germany) and 1 % of pyruvate (Sigma-Aldrich, Germany). All cell lines have been cultivated in the presence of Ra-223, Sm-153 or Re-186 for 24 hours after the monolayer of the cells was created. After the cultivation with Ra-223, Sm-153 or Re-186, the clonogenic survival test was performed and survival curves for all cell lines were constructed. All obtained survival curves correspond to the linearly quadratic model. Sensitivity of both human carcinoma cell lines (adenocarcinoma and glioblastoma cell line) to treatment by all used radionuclides is higher than the sensitivity of the Chinese hamster pulmonary fibroblast cell line. Sensitivity of tested carcinoma or tissue cell lines is higher to alpha treatment than to beta treatment using the same applicated activities of alpha or beta emitters. The achieved results enabled further progress in enhancing the alpha dosimetric studies. (author)

[en] The influence of various hydroxyl radical scavengers such as methanol, ethanol and dimethyl sulfoxide on radiation sensitivity of prokaryotic cells (bacteria Escherichia coli) and eukaryotic cells (yeast Saccharomyces cerevisiae and V79 cells - Chinese hamster pulmonary fibroblasts) irradiated by ⁶⁰Co gamma radiation was investigated. The dependence of radiation sensitivity on dose rate in range from 1.8 to 100 Gy h^-1 was evaluated. Survival of cells irradiated by increasing dose rates was followed using clonogenic assay. Specific protective effect was found to be a nonmonotonous function of dose rate with typical maximum at the dose rate range from 50 to 55 Gy h^-1 in all studied cell types. (authors)

[en] Purpose: To investigate the clinical implications of a variable relative biological effectiveness (RBE) on proton dose fractionation. Using acute exposures, the current clinical adoption of a generic, constant cell killing RBE has been shown to underestimate the effect of the sharp increase in linear energy transfer (LET) in the distal regions of the spread-out Bragg peak (SOBP). However, experimental data for the impact of dose fractionation in such scenarios are still limited. Methods and Materials: Human fibroblasts (AG01522) at 4 key depth positions on a clinical SOBP of maximum energy 219.65 MeV were subjected to various fractionation regimens with an interfraction period of 24 hours at Proton Therapy Center in Prague, Czech Republic. Cell killing RBE variations were measured using standard clonogenic assays and were further validated using Monte Carlo simulations and parameterized using a linear quadratic formalism. Results: Significant variations in the cell killing RBE for fractionated exposures along the proton dose profile were observed. RBE increased sharply toward the distal position, corresponding to a reduction in cell sparing effectiveness of fractionated proton exposures at higher LET. The effect was more pronounced at smaller doses per fraction. Experimental survival fractions were adequately predicted using a linear quadratic formalism assuming full repair between fractions. Data were also used to validate a parameterized variable RBE model based on linear α parameter response with LET that showed considerable deviations from clinically predicted isoeffective fractionation regimens. Conclusions: The RBE-weighted absorbed dose calculated using the clinically adopted generic RBE of 1.1 significantly underestimates the biological effective dose from variable RBE, particularly in fractionation regimens with low doses per fraction. Coupled with an increase in effective range in fractionated exposures, our study provides an RBE dataset that can be used by the modeling community for the optimization of fractionated proton therapy.

[en] According to their physical characteristics, protons and ion beams promise a revolution in cancer radiotherapy. Curing protocols however reflect rather the empirical knowledge than experimental data on DNA repair. This especially holds for the spatio-temporal organization of repair processes in the context of higher-order chromatin structure—the problematics addressed in this work. The consequences for the mechanism of chromosomal translocations are compared for gamma rays and proton beams. - Highlights: ► The majority of DSBs are repaired individually close to the sites of their origin. ► Decondensation of damaged chromatin domains can potentiate clustering of lesions. ► DSB clustering might increase the risk of chromatin translocation. ► Distances of lesions and higher-order chromatin structure influence DSB clustering. ► The conclusions seem to hold both for DSB damage caused by γ-radiation and protons

[en] Cell differentiation is associated with extensive gene silencing, heterochromatinization and potentially decreasing need for repairing DNA double-strand breaks (DSBs). Differentiation stages of blood cells thus represent an excellent model to study DSB induction, repair and misrepair in the context of changing higher-order chromatin structure. We show that immature granulocytes form γH2AX and 53BP1 foci, contrary to the mature cells; however, these foci colocalize only rarely and DSB repair is inefficient. Moreover, specific chromatin structure of granulocytes probably influences DSB induction. - Highlights: ► DSB repair is absent in mature granulocytes with condensed chromatin. ► Repair proteins and γH2AX appear in immature stages but rarely colocalize. ► γH2AX persist long times in these cells and DSB repair is inefficient. ► Even though, γH2AX foci “move” out of the dense chromatin. ► 53BP1 enters HP1β domains only after their decondensation

[en] A comparison between breast cancer cell line MCF7 and human adipose-derived stem cells (ADSC) after irradiation by the same doses of megavoltage X-rays was performed. The cell growth, the induction of apoptosis and the expression of selected genes were analyzed. Irradiated MCF7 related to its control sample grows slower than ADSC and it undergoes apoptosis in much higher levels than ADSC. This was confirmed by real-time polymerase chain reaction as well, where the expression of apoptotic genes was found to be considerably higher for MCF7 than for ADSC. From the results of this project, it could be stated that MCF7 is more radiosensitive than ADSC. (authors)