The role of positron emission tomography following radiosurgical treatment of malignant lung lesions

Abstract

To establish response patterns in PET following stereotactic body radiotherapy (SBRT) of malignant lung lesions. Patients with malignant lung lesions treated with SBRT were retrospectively reviewed. All patients received 40-52 Gy in three to five equal fractions. An independent, blinded radiologist reassessed all 18F-fluoro-deoxy-glucose PET/computed tomography scans to determine the tumor maximum standardized uptake value (SUVmax) and size changes. Thirty-nine patients were included in this study. Of the 47 lesions treated, there were 22 primary and 25 metastatic lung lesions. In total, 86 PET/computed tomography studies were reviewed. The mean SUVmax values decreased markedly and stabilized after 6 months following the treatment of primary lesions. Metastatic lesions showed greater variability, with an overall increase in SUVmax values until 6 months and decrease thereafter. Of the eight local failures, the mean SUVmax and size change from nadir values to biopsy-proven failure were 117 and 215%; however, it was difficult to measure the size of five lesions because of fibrotic changes. Statistical analysis revealed metastatic tumors to be associated with poorer local control (P=0.028). No correlation was found between size or pretreatment SUVmax and outcome. Anticipated SUVmax and size patterns following SBRT remain a challenge due to surrounding tissue reactions. Nonetheless, marked SUVmax changes can aid in determining local failure. Increases in size were also observed in local failures; however, localized fibrosis challenges its utility in distinguishing failures from a normal tissue response. A larger series needs to be examined to better establish the correlation of PET responses to overall survival and local control.