Radiation research
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In 1898, the discovery of two new elements, polonium and radium, reawakened interest in the topic of uranic rays discovered 2 years before by H. Becquerel. Radioactivity, a name coined by Marie Curie, became a major research field for decades. ⋯ It is shown how a well-chosen quantitative method and a systematic approach combining physics and chemistry led to the discovery within less than 1 year. The special role of radium and the determination of its atomic weight by Marie Curie followed by her long-term program for accumulating pure radium salts are emphasized. The first woman with a full professorship at a French University, Marie Curie created and managed the Radium Institute.
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Tumor reoxygenation after irradiation may contribute to a tumor's response to subsequent doses of radiation. The timing of reoxygenation in RIF-1 murine tumors was determined using electron paramagnetic resonance (EPR) oximetry with intratumoral implantation of an oxygen-sensitive paramagnetic material (India ink) to monitor the pO2 in individual murine tumors before, during and after three different irradiation schemes. Radiation was given as a single 20-Gy dose or was split into two 10-Gy doses where the second dose of radiation was delivered at the minimum postirradiation tumor pO2 (24-h interval, hypoxic group) or where the second dose of radiation was delivered after reoxygenation had occurred (72-h interval, oxygenated group). ⋯ There were significantly longer tumor doubling times in the oxygenated compared to the hypoxic group, indicating that the measured changes in pO2 reflected changes in tumor radiosensitivity. A 24-h interval between doses resulted in a delay of reoxygenation in the tumors, while a 72-h interval resulted in a second cycle of hypoxia/reoxygenation. Our results suggest that repeated direct measurements of pO2 in tumors by EPR oximetry could be useful in timing radiation doses to achieve improved local control of tumors.
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Comparative Study
Comparison between pulsed-field gel electrophoresis and the comet assay as predictive assays for radiosensitivity in fibroblasts.
The radiosensitivity of skin fibroblasts derived from patients as measured in vitro by a clonogenic survival assay appears to correlate with the risk of developing severe late reactions to radiation. Unfortunately, these assays are clinically impractical as a predictive test for radiosensitivity. The purpose of this study was to assess the utility of two possible surrogate assays for radiosensitivity, pulsed-field gel electrophoresis (PFGE) and single-cell gel electrophoresis (comet assay), both of which can be used to measure DNA double-strand breaks. ⋯ The slope of the plot of comet moment as a function of dose for each cell line did not correlate with D0.01 (R = 0.36, P > 0.1). In contrast, the slope of the FAR as a function of dose had a weak inverse correlation with D0.01 (R = 0.43 and P = 0.05) such that the more radiosensitive cell lines exhibited a steeper dose response for FAR. Although the correlation between the slope of the dose response for FAR and D0.01 was weak, refinement of the PFGE technique may provide a potentially useful predictive assay for radiosensitivity.
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One of the fundamental tools in radiation biology is a formalism describing time-dose relationships. For example, there is a need for reliable predictions of radiotherapeutic isoeffect doses when the temporal exposure pattern is changed. The most commonly used tool is now the linear-quadratic (LQ) formalism, which describes fractionation and dose-protraction effects through a particular functional form, the generalized Lea-Catcheside time factor, G. ⋯ In terms of applications to radiotherapy, we show that a typical saturable repair formalism predicts practically the same dependences for protraction effects as does the LQ formalism, at clinically relevant doses per fraction. For low-dose-rate exposure, the same equivalence between predictions holds for early-responding end points such as tumor control, but less so for late-responding end points. Overall, use of the LQ formalism to predict dose-time relationships is a notably robust procedure, depending less than previously thought on knowledge of detailed biophysical mechanisms, since various conceptually different biophysical models lead, in a reasonable approximation, to the LQ relationship including the standard form of the generalized time factor, G.
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In a recent study (Int. J. Radiat. ⋯ Oncol. Biol. Phys. 36, 635-639, 1996) provides evidence to support the hypothesis that changes in steady-state tumor lactate levels may serve as sensitive early indices of tumor response to gamma radiation at doses of the order of 2 to 4 Gy.