Cellular Repair Flashcards
Parameters of radiation exposure
- total dose absorbed
- rate at which dose delivered
- quality of the radiation
Acute radiation sickness syndrome
4-24 hrs after exposures
what determines whether subjects live or die after TBI
hematopoietic system
Lethal damage (LD)
irreversible and irreparable
Sublethal Damage (SLD)
repairable in hours unless additional SLD added
Potential Lethal Damage (PLD)
component of radiation damage that can be modified by post irradiation environmental conditions.
LD 50 for radiation
4.5 Gy
CNS syndrome time frame
hours
GI syndrome time frame
3-10 days
Hematopoietic syndrome time frame
30 days
PLD environmental conditions
incubate cells in salt solution. delay mitosis through suboptimal growth conditions –gives DNA chance for repair
PLDR
Potential Lethal Damage Repair - usually occurs in G0 - G1 cells
Culture conditions that facilitate PLDR
- post radiation maintenance
- culture conditions suboptimal for cell cycle progression
- isotonic media or chemicals that inhibit DNA synthesis
SLDR
Sublethal Damage Repair - repair of radiation lesions progresses as a time dependent function
Elkin and Sutton concept
shoulder of the dose-survival curve reflects the ability of the cell to accumulate sublethal radiation damage.
SLD recover time
6 hours
Fractionation
- normal cells recover while tumor cells have less time to repair.
- tumor cells in radioresistant phase in one treatment will be sensitive in next
- re-oxygenation b/w fractions
hyper-fractionation
- small fractions (<2 Gy)
- bronchus, cervix, uteri, head, neck
- less sensitive than late-responding healthy tissues to fraction size
hypo-fractionation
- fewer fractions more than 2 Gy
- similar fractionation sensitivity to healthy tissue
Therapeutic doses
curative cases:
epithelial 60-80 Gy
lymphoma 20-40 Gy
Preventative doses
(aka adjuvant dose)
-45-60 Gy in 1.8 - 2 Gy fractions
Typical Fractionation schedule
1.8-2 Gy per day 5 days per week
Child fractionation dose
1.5-1.8 Gy per day
concomitant boost regimen
two fractions in a single day (used near end of course of treatment)
