Physical and radiobiological parameters of proton beams up to 31 MeV

Summary Frequency distributions of energy deposition in microscopic tissue volumes determined by means of a ?Rossi type? proportional counter for 31, 12 and 8 MeV proton beams and, dose response curves for mortality and chromosome aberrations in cultured human cells exposed to the same beams are analysed with a view to determining suitable parameters to specify radiation quality. The behaviour of quantities LET,Z ^*2/β² and the microdosimetric parameter as a function of energy are compared with the corresponding behaviour of the most significant radiobiological parameters as mean lethal dose per targetD ₀, mean inactivation dose , intensity of chromosome aberrations, and dicentrics. It is shown that is the most suitable physical parameter to characterize the relative effectiveness of protons in the (8÷31) MeV range. Work partially supported by grant No. 8000165896 for the Finalized Project ?Tumor Growth Control?.     

Modeling of waveguide UV-induced Bragg gratings with arbitrary apodization function: Tools for designing high-performance related devices

We present a semi-analytical modeling suitable for the investigation of the spectral characteristics of UV-waveguide Bragg gratings (UV-WBGs) having arbitrary apodization function and extending both in the film layer and in the overlayer. The modeling is based on a proper combination of coupled mode theory and transfer matrix formalism and provides a powerful tool for designing and simulation of complex UV-grating based structures. The results of a detailed investigation of UV-WBGs in doped silica based channel optical waveguides are presented and critical issues for upgrading the performances of related device are discussed. Validation of the modeling is provided by means of an extensive comparison between theoretical and experimental results relevant to UV-WBGs realized in phosphorous (P)- and boron (B)-doped silica based waveguides.     

Radiocarcinogenesis: Results fromin vitro,experiments

Summary Transformation frequencies induced in cell systems by low- and high-LET radiations are compared and analysed as a function of LET and dose protraction. At acute dose rates, the dose-response curve with low-LET radiations shows a complex shape: the transformation frequency increases with the dose by a power of less than 1 in the interval (0.25÷1.5) Gy; a power of about 2 from 1.5 Gy to 4.5 Gy, where it reaches its maximum value and then remains constant. High-LET radiation transformation frequencies increase with dose by a power of 2 from 0.1 to 2 Gy after which they remain constant. RBE values increase with LET up to 140 ke V/μm and then decrease. The transformation frequency is reduced following dose fractionation or dose rate reduction with low-LET radiation, whereas it is enhanced with high-LET radiation, such as 0.85 MeV neutrons. Values of RBE for transformation up to 50 can be evaluated for neutrons. Various models that have been proposed to explain these results are analysed and compared.

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Riassunto Si riportano i risultati di uno studio della frequenza di trasformazione indotta in cellule in coltura da radiazione ionizzante in funzione della dose, del LET e della distribuzione temporale della dose. Per radiazioni a basso LET, l’andamento della curva dose-effectto è piuttosto complesso: la frequenza di trasformazione cresce con una potenza della dose minore di 1 nella regione di dosi (0.25÷1.5) Gy, di circa 2 nella regione da 1.5 Gy a 4.5 Gy oltre la quale si mantiene costante. La frequenza di trasformazione indotta da radiazioni ad alto LET aumenta con la dose con una potenza di 2 tra 0.1 e 2 Gy dove raggiunge il suo valore massimo e poi si mantiene costante. I valori di RBE aumentano con il LET fino a 140 keV/μm e poi decrescono in analogia con quanto trovato per altri effetti quqli la mortalità e l’aberrazione cromosomica. Il frazionamento e la riduzione dell’intensità di dose di radiazione a basso LET producono una diminuzione dell’incidenza di trasformazione; al contrario, alcune radiazioni ad alto LET quali neutroni da 0.85 MeV si sono mostrate molto piú efficaci, mostrando un netto aumento della frequenza di trasformazione quando la dose viene somministrata in piú frazioni od a ridotta intensità nell’intervallo di dosi minori di 1.5 Gy. Alla luce di questi dati si discutono e si analizzano diversi modelli d’induzione della trasformazione proposti in letteratura.

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Резюме Частоты преобразований, индуцированные в клеточных системах излучениями с малыми и высокими ЛПЭ, сравниваются и анализируются в зависимости от ЛПЭ и дозы облучения. При больших интенсивностях кривая ?дозаотклик? при излучениях с малыми ЛПЭ обнаруживает сложное поведение: частоты преобразований увеличиваются с дозой, как степенная функция с показателем меньше 1 в интервале (0.25÷1.5) Gy; потом с показателем 2 в интервале от 1.5 до 4.4 Gy, где достигают максимальной величины, а затем остаются постоянными. Частоты преобразованнй при излучениях с высокими ЛПЭ увеличиваются с дозой, как степенная функция с показателем 2 в интервале от 0.1 до 2 Gy, а затем остаются постоянными. Величины RBE увеличиваются с ЛПЭ вплоть до 140 кэВ/мкм, а затем уменьшаются. Частота преобразований уменьшается с уменьшением интенсивности дозы в случае излучений с низкими ЛПЭ, тогда как для излучений с высокими ЛПЭ, например, нейтроны с энергией 0.85 МэВ, частота преовразований возрастает. Для нейтронов можно оценить величины RBE для преобразований вплоть до 50. Анализируются и сравниваются различные модели, предложенные для объяснения этих результатов.

     

Radiocarcinogenesis in vitro: «Inverse dose-rate effect»

Summary There is substantial experimental evidence that protracted exposure to high-LET radiation can have a greated effect than single exposure in inducing cell transformation, the so-called ?inverse dose-rate effect?. The magnitude of this enhancement is due to the complex interplay between dose, dose rate and radiation quality. We have developed a model that explains the complex trend of the experimental results. This model is based on the assumption that there is a brief period of high sensitivity to transformation in the cell cycle as proposed in the literature and takes into account the saturation observed at high doses in the dose-effect curves. Specific equations are reported for acute, protracted and fractionated irradiation. Findings with C3H10T1/2 cells were analised in the light of this model. Assuming best fitted parameters of the model obtained from acute-irradiation data, tranformation frequencies due to protracted or fractionated exposure were predicted and compared with experimental findings on fission and monoenergetic neutrons and on charged particles of LET between 20 and 150 keV/μm. The model’s predictions were found to be closely consistent with the available experimental data.