Radiation induced lung fibrosis usually presents as a focal, non-anatomic pattern of fibrosis.
Radiation induced lung fibrosis does not have a clear straight line of demarcation.
There are two clinical stages of radiation induced lung disease: the first stage is early and transient pneumonitis, which usually occurs within 4-12 weeks of radio therapy.
The second stage is chronic fibrosis, which could take approximately 6-24 months to evolve after radiation.
The diagnosis requires ruling out and infectious etiology for the fibrosis.
The average incidence of radiation induced lung fibrosis is 16-28%.
It is hypothesized that activation of myofibroblasts occurs following ionizing radiation.
Occurs approximately 1 year after completion of radiation and is usually irreversible.
The probability of fibrosis is twice as great with accelerated fractionation as with once daily fractionation.