Imaging follow-up after stereotactic ablative radiotherapy (SABR) for lung tumors

Stereotactic ablative radiotherapy (SABR), also named stereotactic body radiation therapy, entails the delivery of individual ablative doses of radiation to the tumor volume with a very steep dose gradient beyond the tumor volume using highly conformal techniques and has been used to treat primary and metastatic lung tumors with promising results achieved. As a result of the delivery of individual ablative doses to the lung, the resulting inflammatory (acute) and fibrotic (late) reactions are more intense, rendering interpretation of post-SABR imaging changes difficult. Different early and late injury patterns have been described based on computerized tomography (CT) by various groups of researchers. Although the data on post-SABR imaging changes are emerging, there are still challenges distinguishing between post-treatment changes and tumor progression. The necessity for evaluation based on serial imaging cannot be overemphasized. Controversies still exist as to whether CT or positron emission tomography (PET) should be used for follow-up. Since CT and PET are the most commonly used imaging modalities for follow-up after SABR, they will be the foci of this review article.