Evidence for a Dose-rate Effect in Type B Spermatogonia of the Mouse at High Dose-rates

ABSTRACTThe temperature dependence of the so-called reverse dose rate effect for generation of vacancy-type defects in silicon has been investigated using samples implanted with 1.3 MeV protons at temperatures between 70 and 300 K. The effect is found to involve a thermally controlled process which exhibits an activation energy of ∼0.065 eV, possibly associated with rapid migration of Si self-interstitials (I). Further, using a concept of dual Si ion-implants long range migration of I:s at room temperature has been studied. Annihilation of vacancy-type defects at a depth of ∼3 μm is obtained by injection of I:s from a shallow implant with sufficiently high dose.

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509 Poster Dose-rate effect as a predictor of late bladder complications following high-dose-rate intracavitary radiotherapy in carcinoma of the cervix

Radiotherapy and Oncology ◽

10.1016/s0167-8140(02)82820-1 ◽

2002 ◽

Vol 64 ◽

pp. S162

Keyword(s):

Dose Rate ◽

High Dose Rate ◽

Rate Effect ◽

High Dose ◽

Dose Rate Effect

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Basic Properties of a New Polymer Gel for 3D-Dosimetry at High Dose-Rates Typical for FFF Irradiation Based on Dithiothreitol and Methacrylic Acid (MAGADIT): Sensitivity, Range, Reproducibility, Accuracy, Dose Rate Effect and Impact of Oxygen Scavenger

Polymers ◽

10.3390/polym11101717 ◽

2019 ◽

Vol 11 (10) ◽

pp. 1717 ◽

Cited By ~ 1

Author(s):

Muzafar Khan ◽

Gerd Heilemann ◽

Wolfgang Lechner ◽

Dietmar Georg ◽

Andreas Georg Berg

Keyword(s):

Ascorbic Acid ◽

Radiation Therapy ◽

Dose Rate ◽

Methacrylic Acid ◽

Polymer Gels ◽

High Dose ◽

Polymer Gel ◽

Oxygen Scavenger ◽

Dose Rates ◽

Dose Rate Effect

The photon induced radical-initiated polymerization in polymer gels can be used for high-resolution tissue equivalent dosimeters in quality control of radiation therapy. The dose (D) distribution in radiation therapy can be measured as a change of the physical measurement parameter T2 using T2-weighted magnetic resonance imaging. The detection by T2 is relying on the local change of the molecular mobility due to local polymerization initiated by radicals generated by the ionizing radiation. The dosimetric signals R2 = 1/T2 of many of the current polymer gels are dose-rate dependent, which reduces the reliability of the gel for clinical use. A novel gel dosimeter, based on methacrylic acid, gelatin and the newly added dithiothreitol (MAGADIT) as an oxygen-scavenger was analyzed for basic properties, such as sensitivity, reproducibility, accuracy and dose-rate dependence. Dithiothreitol features no toxic classification with a difference to THPC and offers a stronger negative redox-potential than ascorbic acid. Polymer gels with three different concentration levels of dithiothreitol were irradiated with a preclinical research X-ray unit and MR-scanned (T2) for quantitative dosimetry after calibration. The polymer gel with the lowest concentration of the oxygen scavenger was about factor 3 more sensitive to dose as compared to the gel with the highest concentration. The dose sensitivity (α = ∆R2/∆D) of MAGADIT gels was significantly dependent on the applied dose rate D ˙ (≈48% reduction between D ˙ = 0.6 Gy/min and D ˙ = 4 Gy/min). However, this undesirable dose-rate effect reduced between 4–8 Gy/min (≈23%) and almost disappeared in the high dose-rate range (8 ≤ D ˙ ≤ 12 Gy/min) used in flattening-filter-free (FFF) irradiations. The dose response varied for different samples within one manufacturing batch within 3%–6% (reproducibility). The accuracy ranged between 3.5% and 7.9%. The impact of the dose rate on the spatial integrity is demonstrated in the example of a linear accelerator (LINAC) small sized 5 × 10 mm2 10 MV photon field. For MAGADIT the maximum shift in the flanks in this field is limited to about 0.8 mm at a FFF dose rate of 15 Gy/min. Dose rate sensitive polymer gels likely perform better at high dose rates; MAGADIT exhibits a slightly improved performance compared to the reference normoxic polymer gel methacrylic and ascorbic acid in gelatin initiated by copper (MAGIC) using ascorbic acid.

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Dose-rate effect of ultrashort electron beam radiation on DNA damage and repair in vitro

Journal of Radiation Research ◽

10.1093/jrr/rrx035 ◽

2017 ◽

Vol 58 (6) ◽

pp. 894-897 ◽

Cited By ~ 7

Author(s):

Nelly Babayan ◽

Galina Hovhannisyan ◽

Bagrat Grigoryan ◽

Ruzanna Grigoryan ◽

Natalia Sarkisyan ◽

...

Keyword(s):

Dna Damage ◽

Electron Beam ◽

Dose Rate ◽

Rate Effect ◽

High Dose ◽

Distribution Analysis ◽

Beam Radiation ◽

Dna Damages ◽

Dna Damage And Repair ◽

Dose Rate Effect

Abstract Laser-generated electron beams are distinguished from conventional accelerated particles by ultrashort beam pulses in the femtoseconds to picoseconds duration range, and their application may elucidate primary radiobiological effects. The aim of the present study was to determine the dose-rate effect of laser-generated ultrashort pulses of 4 MeV electron beam radiation on DNA damage and repair in human cells. The dose rate was increased via changing the pulse repetition frequency, without increasing the electron energy. The human chronic myeloid leukemia K-562 cell line was used to estimate the DNA damage and repair after irradiation, via the comet assay. A distribution analysis of the DNA damage was performed. The same mean level of initial DNA damages was observed at low (3.6 Gy/min) and high (36 Gy/min) dose-rate irradiation. In the case of low-dose-rate irradiation, the detected DNA damages were completely repairable, whereas the high-dose-rate irradiation demonstrated a lower level of reparability. The distribution analysis of initial DNA damages after high-dose-rate irradiation revealed a shift towards higher amounts of damage and a broadening in distribution. Thus, increasing the dose rate via changing the pulse frequency of ultrafast electrons leads to an increase in the complexity of DNA damages, with a consequent decrease in their reparability. Since the application of an ultrashort pulsed electron beam permits us to describe the primary radiobiological effects, it can be assumed that the observed dose-rate effect on DNA damage/repair is mainly caused by primary lesions appearing at the moment of irradiation.

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Diminished or inversed dose-rate effect on clonogenic ability in Ku-deficient rodent cells

Journal of Radiation Research ◽

10.1093/jrr/rraa128 ◽

2020 ◽

Author(s):

Hisayo Tsuchiya ◽

Mikio Shimada ◽

Kaima Tsukada ◽

Qingmei Meng ◽

Junya Kobayashi ◽

...

Keyword(s):

Cell Survival ◽

Dose Rate ◽

Biological Effects ◽

Severe Combined Immunodeficiency ◽

High Dose Rate ◽

Rate Effect ◽

High Dose ◽

Γ Ray ◽

Clonogenic Cell ◽

Dose Rate Effect

Abstract The biological effects of ionizing radiation, especially those of sparsely ionizing radiations like X-ray and γ-ray, are generally reduced as the dose rate is reduced. This phenomenon is known as ‘the dose-rate effect’. The dose-rate effect is considered to be due to the repair of DNA damage during irradiation but the precise mechanisms for the dose-rate effect remain to be clarified. Ku70, Ku86 and DNA-dependent protein kinase catalytic subunit (DNA-PKcs) are thought to comprise the sensor for DNA double-strand break (DSB) repair through non-homologous end joining (NHEJ). In this study, we measured the clonogenic ability of Ku70-, Ku86- or DNA-PKcs-deficient rodent cells, in parallel with respective control cells, in response to high dose-rate (HDR) and low dose-rate (LDR) γ-ray radiation (~0.9 and ~1 mGy/min, respectively). Control cells and murine embryonic fibroblasts (MEF) from a severe combined immunodeficiency (scid) mouse, which is DNA-PKcs-deficient, showed higher cell survival after LDR irradiation than after HDR irradiation at the same dose. On the other hand, MEF from Ku70−/− mice exhibited lower clonogenic cell survival after LDR irradiation than after HDR irradiation. XR-V15B and xrs-5 cells, which are Ku86-deficient, exhibited mostly identical clonogenic cell survival after LDR and HDR irradiation. Thus, the dose-rate effect in terms of clonogenic cell survival is diminished or even inversed in Ku-deficient rodent cells. These observations indicate the involvement of Ku in the dose-rate effect.

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