Functional Image-guided Radiotherapy Planning for Normal Lung Avoidance: a Review.

For patients with lung cancer undergoing curative intent radiotherapy, functional lung imaging can be incorporated into treatment planning to modify the dose distribution within non-target volume lung by differentiation of lung regions that are functionally defective or viable. This concept of functional image-guided lung avoidance treatment planning has been investigated with several imaging modalities, primarily single photon emission computed tomography (SPECT), but also hyperpolarised gas magnetic resonance (MR) imaging, positron emission tomography (PET) and computed tomography (CT)-based measures of lung biomechanics. Here, we review the application of each of these modalities, review practical issues of lung avoidance implementation, including image registration and the role of both ventilation and perfusion imaging, and provide guidelines for reporting of future lung avoidance planning studies.