Department of Diagnostic and Interventional Radiology, Marien Hospital, Düsseldorf, Germany
Radiation therapy of malignancy in the chest may expose normal pulmonary parenchyma to radiation.
This may lead to radiation pneumonitis which may be clinically occult or present with symptoms such as dyspnoea, fever and dry cough depending on the proportion of lung parenchyma involved and individual susceptibility of the patient [1, 2, 3].
Radiation pneumonitis usually does not occur at lung doses below 30 Gray (Gy) whereas it develops almost always with doses above 40 Gy. In doses between 30 and 40 Gy individual features such as pre-existing lung disease, simultaneous chemotherapy or other medical therapy increase the likelihood of radiation pneumonitis.
Radiological abnormalities in radiation pneumonitis follow a typical time course: After the threshold dose has been reached there is a delay of 4 to 6 weeks with no radiological abnormalities. Subsequently ground glass opacities develop which increase in density to form consolidation within another 4 to 6 weeks. Consolidation persists for some months and resolves incompletely with residual fibrotic changes within the next weeks and months.
Following radiation therapy that did not lead to radiation pneumonitis initially, additional medical therapy with pneumotoxic drugs at a later stage may then cause manifest radiation pneumonitis (rebound/recall pneumonitis).
A pathognomonic feature of radiation pneumonitis is the fact that the location of ground glass opacities and consolidation precisely mirrors the radiation port, i.e. the area of pulmonary parenchyma exposed to radiation above the threshold dose while completely ignoring any anatomical borders such as segmental or lobar borders.
This is easily recognised with simple radiation ports such as anterior-posterior/posterior-anterior (AP-PA) radiation fields but is more difficult to recognise in modern complex radiation ports such as intensity-modulated radiation therapy (iMRT), stereotactic radiation therapy, cyber knife or gamma knife therapy etc. [4, 5].
Furthermore, radiation therapy of the chest is a recognised cause of organizing pneumonia (OP) . In contrast to radiation pneumonitis consolidation or ground glass opacities in radiation-induced OP does not mirror the radiation port and may include pulmonary parenchyma outside the radiation field and has a very heterogeneous time course with OP developing only days but also moths after radiation therapy.
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