Evaluating PET-based functional imaging changes in the heart after thoracic chemo-radiation

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International Journal of Radiation Oncology, Biology, Physics


Purpose/Objective(s): The importance of the heart has been emphasized in recent thoracic chemo-radiation (CRT) literature. A lung cancer dose escalation study (RTOG 0617) noted that heart doses were significantly associated with overall survival (OS). The purpose of this study was to characterize pre-to-post treatment cardiac metabolic changes using FDGPET scans and to evaluate whether PET-based cardiac imaging changes predicted for OS. Materials/Methods: Lung cancer patients enrolled on a multi-institutional, prospective clinical trial for functional avoidance thoracic radiotherapy were analyzed. 39 patients who had undergone pre and post chemo-radiation FDG-PET imaging were studied. Post-CRT PET scans were acquired at a median time of 97 days (range 11 to 477 days) after treatment. Patients on the study were treated with definitive CRTwith radiation doses ranging from 45- 60 Gy in 15-30 fractions. For each patient, the pre-treatment PET-CT and post-treatment PET-CTwere rigidly registered to the planning CT, dose, and structure set. PET-based dose-response was assessed by comparing pretreatment to post-treatment Standardized Uptake Values (SUV) in the heart contour. A dose-response curve was generated by binning each voxel in the heart contour into 10 Gy dose-bins and analyzing the average SUV changes in each dose-bin. Patients on the study were followed for OS for up to 14 months after completing chemo-radiation. We evaluated whether the pre-topost treatment changes in the average or maximum SUV were predictive of OS. The OS analysis was performed by comparing mean SUV changes for patients that were alive or had died at last follow-up and by using a univariate cox proportional hazard model to assess whether pre-to-post treatment SUV changes were a significant predictor of OS. Results: The cardiac SUV dose-response curve revealed increasing changes in SUV as a function of dose with relative SUV increases of 11.4%, 9.8%, 9.4%, 12.2%, 14.2%, and 20.1% in the 10, 20, 30, 40, 50, and 60 Gy dose-bins, respectively. The SUV dose-response curve demonstrated an average increase of 1.7% for every 10 Gy. Median followup was 410 days (range 181 to 541) with 30/39 patients alive at last followup. Patients that were alive at follow up had an average increase of +17.2% in cardiac SUV while patients that did not survive had a decrease in SUV of -13.5% (pZ0.048). Both the mean and maximum pre to post-treatment SUV changes were significant predictors (p<0.03) of OS. Conclusion: Functional imaging has been used for target delineation and evaluating normal lung function in thoracic CRT but has yet to be used for cardiac treatment response assessment. In our dataset, post-treatment changes in cardiac PET were significant indicators of dose-response and potential predictors of OS. Pre and post-treatment PET imaging is frequently obtained for lung cancer patients and if validated by multivariate analysis, our data show the potential for PET cardiac changes to be an early predictor for cardiac death, allowing for intervention.





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