Abstract
Differentiating local recurrence from post-treatment changes on PET scans following stereotactic ablative radiotherapy (SABR) or hyperfractionation for lung tumors is challenging. We performed a prospective pilot study of 3-deoxy-3-[18F]-fluorothymidine (FLT)-PET-CT in patients with equivocal post-radiation FDG-PET-CT to assess disease recurrence.Methods: We prospectively enrolled 10 patients, 9 treated with SABR and 1 with hyperfractionated external beam radiotherapy for thoracic malignancy with subsequent equivocal follow-up FDG-PET-CT, to undergo FLT-PET-CT prior to biopsy or serial imaging. FLT-PET scans were interpreted by a radiologist with experience in reading FLT-PET-CT and blinded to the results of any subsequent biopsy or imaging.Results: Of the 10 patients enrolled, 8 were evaluable after FLT-PET-CT. Based on the FLT-PET-CT, a blinded radiologist accurately predicted disease recurrence vs. inflammatory changes in 7 patients (87.5%). The combination of higher lesion SUVmax and higher ratio of lesion SUVmax to SUVmax of mediastinal blood pool was indicative of recurrence. Qualitative assessment of increased degree of focality of the lesion also appears to be indicative of disease recurrence.Conclusion: Adjunctive FLT-PET-CT imaging can complement FDG-PET-CT scan in distinguishing post-treatment radiation changes from disease recurrence in thoracic malignancies. These findings support the investigation of FLT-PET-CT in a larger prospective study.
Highlights
Stereotactic ablative radiotherapy (SABR) is increasingly used for the definitive treatment of early-stage non-small cell lung cancer (NSCLC), as well as for oligometastatic lesions and other sites of disease including liver, pancreas, prostate [1,2,3,4,5]
Three patients had findings interpreted as negative for recurrence on FLT-positron emission tomography (PET)-computed tomography (CT) scan and the absence of recurrence subsequently confirmed by biopsy or serial imaging (Table 2)
FLTPET-CT is perhaps most widely used in the setting of lymphoma, where very early changes in [18F]-FLT uptake following chemotherapy have been correlated with treatment response [21]
Summary
Stereotactic ablative radiotherapy (SABR) is increasingly used for the definitive treatment of early-stage non-small cell lung cancer (NSCLC), as well as for oligometastatic lesions and other sites of disease including liver, pancreas, prostate [1,2,3,4,5]. Compared to computed tomography (CT) which provides morphological information, positron emission tomography (PET) informs on tumor metabolism which may be more accurate in evaluating early response to therapy [7]. [18F]-fluorodeoxyglucose-positron emission tomography (FDG-PET) has been an important tool in the evaluation of treatment response after radiotherapy, and metabolic activity on follow-up FDG-PET-CT in previously treated tumors has been used as a biomarker of response to treatment [8]. The difficulty interpreting FDG-PET-CT scans after SABR frequently results in unnecessary imaging and biopsy to evaluate local recurrence of disease [13]
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