1. Cellular Radiobiology
Chapter 32
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2. Target Theory DNA is the target molecule Cell death only occurs if
target molecule is inactivated
Hits can be indirect or direct 2
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3. HITS LOW LET & OER = low Probability of target hits
O2 presence = free radicals
And increased volume leading
To an increased hit probability
High LET = close ionizations
And an increase hit probability
O2 presence = no extra hits;
Max # hits there with direct and high LET 3
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4. Cell-Survival Kinetics
Single-Target, Single-Hit Model: biological targets (bacteria)
Multitarget, Single-Hit Model: human cells -dose threshold
Random rain drops and ratio of wet to dry squares.
Increased # or drops = decreased # of dry squares
After irradiation of 1000 cells, the dose-response is exponential D37 is the dose that results in 37% survival. 4
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5. Cell-Survival Kinetics cont.
Low D37 = High radiosensitivity (more surviving cells)
Split squares require both halves to be hit for square to be wet
Multitarget, single hit model of cell survival is characteristic of human cells
Do is mean lethal dose; Dq is threshold dose 5
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6. Recovery
Some damage must be accumulated before the cell dies; this is called sublethal damage
The wider the shoulder of the graph the more sublethal damage
For full recovery the time between each split cell dose must be at least as long as the cell generation time, usually 24 hrs
G1 is the most time variable of the cell phases
Human cells are most radiosensative in M phase and most radioresistant in late S
See next two slides for pictures 6
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7. Split-dose Irradiation7
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8. Cell-Cycle Effects 8
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9. RBE and OER O2 presence maximizes the effect of low-LET radiation
High-LET show little difference with O2 presence
RBE and OER
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10. THE END Exam Next week 9:30 – 11 AM HSH for Second Group 8-9:30
Faculty going to ACERT PM