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Functional lung imaging in thoracic cancer radiotherapy.

BACKGROUND
Lung cancer is the No. 1 cancer killer of both men and women in the United States. Radiotherapy is frequently employed as part of the treatment. However, radiation must traverse surrounding regions of normal lung, potentially inducing pulmonary toxicity. Because these patients frequently have underlying lung disease, a radiation-induced decrement in lung function could be highly morbid or even fatal. It is well known that lung function is not uniform, with wide ranges of ventilation and perfusion levels throughout the lung. Currently radiation oncologists do not have the ability to account for this variation when generating treatment plans.


METHODS
This article reviews some techniques used to assess pulmonary ventilation and perfusion, including nuclear medicine, magnetic resonance imaging (MRI) and computed tomography (CT).


RESULTS
Many techniques have the potential to be used in radiotherapy treatment planning for thoracic cancer patients to spare normal functional lung volumes while delivering adequate radiation dose to the tumors. The article outlines a promising new technique to generate 3-D ventilation maps by using deformable image registration of 4-D CT image sets.


CONCLUSIONS
While there are some technical challenges to overcome before pulmonary functional imaging can be routinely employed clinically in radiation oncology, there is the potential to preferentially spare better perfused/ventilated regions of normal lung, which promises to reduce pulmonary toxicity.