Radiation Necrosis

Necrosis of brain following radiation can be seen as an early delayed complication or late delayed complication.
The early delayed radiation necrosis may be seen with in 2 months of irradiation (Range 1 to 4 Months). This is a very rare entity. The pathological process might represent an autoimmune response following sensitization by a necrobiotic process induced by radiation.

The late delayed radiation necrosis commonly presents as a mass lesion.
The true incidence and natural history of late delayed radiation necrosis are not known. Most commonly late delayed radiation affects present at a mean duration of 14 months, but can occur as early as 6 months or as late as 5 years after completion of treatment.
The primary mechanism of the late delayed radiation necrosis is coagulative necrosis affecting the white matter secondary to small artery endothelial injury or direct damage to oligodendroglia.
Its incidence has been estimated as 5% in patients who have received greater than 45 Gy in fractions of 2 Gy per day.
25% of patients may suffer from radiation necrosis if the areas of the brain have received a total radiation dose of 60Gy or more.
4 facors critical in the occurance of radiation necrosis are
1. Total dose of radiation
2. Overall time of administration
3. Size of each fraction of Radiation
4. Number of fractions per irradiation