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Oxygen in S Pahse of a Cell Cycle

S Akber

S Akber1*, (1) Consulting Physicist, Lorain, OH

SU-E-T-310 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose:: Variation in cell sensitivity through the cell cycle has an important radiobiological implication in cancer treatment. The reasons for the cell sensitivity changes through the cell cycles are not well understood. It is generally agreed that the s-phase is radio resistant because of its deficiency of molecular oxygen. This conclusion is based on the Oxygen Enhancement Ratio (OER) and not by measuring the actual molecular oxygen content in each phase of the cell cycles. It appears that S phase of Hela Cell has more oxygen than M phase.

Methods: Nuclear Magnetic Resonance (NMR) spin lattice relaxation time (T1) along with mean lethal radiation dose (Do) and OER in M, G1 and S phase of Hela cells are abstracted from the literature. Analysis of the data reveals that T1 correlates very well indeed with Do and OER.

Results: The decrease in T1 from M to S phase of Hela Cells is due to molecular oxygen yielding a correlation of 0.77. Whereas OER increases with the aging of the cell cycle yielding a correlation of 0.79 with T1. It indicates that S phase has more oxygen than M phase.

Conclusion: T1 is a very sensitive index of molecular oxygen concentration in cells. The decrease in T1 from M phase to S phase of Hela cell by 50% is most likely due to high molecular oxygen content in S phase. OER increases with the aging of the cell cycles. Higher OER in S phase also clearly indicates higher oxygen content. It also appears to have little or no significant effect on OER if radiation energy increases from 280 kV to 1.25 MeV.

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