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Why does fractionation reduce risk of late effects?
• Individual dose fractions create lethal (fixed) and sub-
lethal (repairable) damage.
• Sub-lethal damage (SLD) repairs between one fraction
and the next.
• Normal tissues generally have a greater capacity to
repair SLD than tumours.
• The process of fractionation therefore “spares” the
normal tissues relatively more than the tumour.
• If fewer, larger fractions are delivered, normal tissue
damage
may
be excessive, i.e. tolerance may be
exceeded.