5. PROLIFERATION AS A FACTOR
IN
NORMALTISSUE
0 5 12 19 26 33 days
1
4
1
0
5
0
Extradoserequired(Gy)
Extra dose required to
counteract proliferation in
skin (Gy)
Corresponds to
4 weeks in the
human 1.3 Gy per Day
Time after first fraction in the mouse
x 3 Gy each fraction
Total dose required
to produce a given
biologic effect is
NOT a power
function of time, as
postulated by Ellis
but more complex
6. • Early responding tissues- are triggered to
proliferate within few wks after start of
fractionated RT
whereas
• late responding tissues –the time at which extra
dose is required compensate for its proliferation in
humans is far beyond the overall time of any
normal radiotherapy regimen .
Prolonging overall treatment time has
large sparing effect on early reactions
but little sparing effect on late
reactions.
7. RADIATION RESPONSE
• Response of all normal tissues to radn are DIFFERENT.
• Depending on their response tissues are either
• Early responding – constitute fast proliferating cells such as skin,
mucosa, intestinal epithelium, colon, testis etc.
• Late responding – have large no. of cells in the resting phase e.g.
spinal cord, bladder, lung, kidneys etc.
8.
9.
10.
11.
12.
13.
14. and overall
treatment time both
Radioresistance is because of a
major portion of cells in S phase.
Reason of radioresistance.
large number of cells in Resting Phase
23. CONVENTIONAL FRACTIONATION
• Convenient (no weekend treatment)
• Efficient (treatment every weekday)
• Effective (high doses can be delivered without
exceeding either acute or chronic normal tissue
tolerance)
• Allows upkeep of machines.
• Most tried & trusted method
• Both tumorocidal & tolerance doses are well
documented
24. Fraction size--- Same 1.8 – 2 Gy
■ Fraction number--- Same
■Total treatment time-- Short –Eg. twice per day, or > 5 fractions/per
week
■ Rationale : reduce tumor repopulation during RT.
■ Disadvantage : Severe acute reaction .
■ Pure accelerated treatment – same total dose delivered in half the
overall time by giving 2 or more fractions/day. Severe acute effects
are limiting factor.
■ Impure accelerated treatment – dose is reduced or rest period is
interposed in the middle of treatment
II IIIIIIII IIIIIIIIII IIIIIIIIII IIIIIIIIII IIIIIIIIII 150-200 cGy X 2 per day; 5 days a week
25. EORTC 22851:
• 15% increase in loco regional control
• No survival adv.
• Increased acute effects
• Unexpected increase in late complications
28. SPLIT-COURSE
• to allow elderly pts. to recover from acute reactions
of treatment
• to exclude pts. from further morbidity who have
poorly tolerated 1st half or disease progressed
despite treatment.
