Mudundi R. Raju

Radiological physics characteristics of the extracted heavy ion beams of the bevatron.

Studies of the depth-ionization properties and the biological effects of heavy ion beams produced at the bevatron have extended work previously done with less energetic beams from other sources. Results indicate that heavy ion beams are suitable for tumor therapy, studies relating to space biology, and fundamental radiobiology.

Oxygen enhancement ratio as a function of dose and cell cycle phase for radiation-resistant and sensitive CHO cells.

There is still controversy over whether the oxygen enhancement ratio (OER) varies as a function of dose and cell cycle phase. In the present study, the OER has been measured as a function of survival level and cell cycle phase using volume flow cell sorting. This method allows both the separation of cells in different stages of the cycle from an asynchronously growing population, and the precise plating of cells for accurate measurements at high survival levels. We have developed a cell suspension gassing and sampling system which maintained an oxygen tension less than 20 ppm throughout a series of sequential radiation doses. For both radiation-resistant cells (CHO-K1) and a radiation-sensitive clone (CHO-xrs6), we could separate relatively pure populations of G1-phase, G1/S-boundary, S-, and G2-phase cells. Each cell line showed a typical age response, with cells at the G1/S-phase boundary being 4 (CHO-K1) to 12 (CHO-xrs6) times more sensitive than cells in the late S phase. For both cell lines, G1-phase cells had an OER of 2.3-2.4, compared to an OER of 2.8-2.9 for S-phase and 2.6-2.7 for G2-phase cells. None of these age fractions showed a dependence of OER on survival level. Asynchronously growing cells or cells at the G1/S-phase boundary had an OER similar to that of G1-phase cells at high survival levels, but the OER increased with decreasing survival level to a value near that of S-phase cells. These results suggest that the decrease in OER at high survival levels for asynchronous cells may be due to differences in the OERs of the inherent cell age subpopulations. For cells in one cell cycle stage, oxygen appears to have a purely dose-modifying effect.

A Calculation of the Physical Characteristics of Negative Pion Beams: Energy-Loss Distribution and Bragg Curves

Calculations have been made of the dE/dx distribution (LET spectrum) and central-axis depth-dose curves (Bragg curves) of stopping negative pion beams in water. Such beams are of interest because of the large deposition of energy at depth in the stopping pion region relative to that deposited at the surface. Nuclear interactions occurring when the pions come to rest cause low-energy highly ionizing particles to be emitted as the capturing nucleus breaks up, thus increasing the dose deposited in the stopping pion region. The calculations show that, for beams similar to those presently available experimentally, peak depth-to-entrance ratios of 3.4 and 2.9 can be expected in the absorbed dose in water for pure and contaminated beams, respectively, with a width of around 3.5 cm. The contaminated beam was assumed to contain 65% pions, 10% muons, and 25% electrons. The pions in these beams have a range of 25 cm of water. Comparison with experimental results taken with a lithium-drifted silicon detector shows th...

Coulter volume cell sorting to improve the precision of radiation survival assays

A new method for measuring cell survival at low doses of ionizing radiation has been developed through the use of flow cytometric cell sorting on the basis of Coulter volume signals. The cell sorter is capable of deflecting a precisely known number of cells directly into culture dishes, thus eliminating any errors associated with cell dilution and volume sampling. The use of Coulter volume signals as the sorting parameter is shown to be noncytotoxic for a variety of cell lines. Comparison of radiation survival curves measured above the 10% survival level by either the cell sorter or standard dilution assay demonstrates the increased precision of the cell sorter technique . Because of these advantages of cell sorting over conventional methods of plating cells, this technique has many applications in the field of radiation biology and other studies of cell survival.

Induction of heteroallelic reversions and lethality in Saccharomyces cerevisiae exposed to radiations of various LET ( 60 Co rays, heavy ions and - mesons) in air and nitrogen atmospheres.

Induction of heteroallelic reversion in diploid yeast is one of the most radiosensitive processes known. Reversion to arginine independence in a diploid strain BZ34 of Saccharomyces cerevisiae was used to measure the relative biological effectiveness (RBE) of π- mesons and heavy ions. Exposures were also conducted under anoxic conditions to obtain the oxygen enhancement ratio (OER) for these radiations and for60 Co γ rays. The linear energy transfer (LET) values used covered a range from 3 to 5500 MeV

Human Cell Survival as a Function of Depth for a High-Energy Neon Ion Beam

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The Oxygen Effect of π- Mesons in Vicia faba

. The OER values obtained for60 Co γ rays and π- mesons were 2.5 and 1.9, respectively. The response of this yeast system was found to be nearly the same at dose rates of 40 rads/hr and 40 rads/min of60 Co γ rays. With increasing LET, the RBE rose to a maximum value in the region 2000 MeV

Effect of Negative Pions on the Proliferative Capacity of Ascites Tumor Cells (Lymphoma) in Vivo

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INFLUENCE OF LINEAR ENERGY TRANSFER ON THE RADIORESISTANCE OF BUDDING HAPLOID YEAST CELLS.

, corresponding to that of carbon ions. The OER decreased with increasing LET, approaching unity for neon ions. The study was extended to induction of lethality with t...

The RBE of negative pions in 2-day-old ascites tumors.

Cultured human kidney cells were irradiated while suspended in a gelatin cylinder using a 400-MeV/u neon ion beam produced by the Berkeley BEVALAC. The Bragg peak was transformed to a width of 4 cm with a ridge filter, and cell survival (colony-forming ability) was determined as a function of depth and dose. A cell survival curve in the broadened peak region appeared to be exponential, and RBE values in the peak and plateau regions were approximately 3.0 and 1.8, respectively, at the 10 percent survival level. Thus, the results indicate that the biological effect is enhanced even when the narrow peak is broadened. The secondary particles (ions lighter than neon and neutrons) produced by neon ions do not cause much cell killing beyond the range of neon ions and, thus, do not seem to be a limiting factor for the use of neon ion beam in radiotherapy.(auth)