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18F-FDG PET Imaging to Improve RT Treatment Outcome for Locally Advanced Lung Cancer

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N Shusharina

N Shusharina*, F Khan, G Sharp, N Choi, Massachusetts General Hospital, Boston, MA


SU-E-J-124 (Sunday, July 12, 2015) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: To investigate spatial correlation between high uptake regions of pre- and 10-days-post therapy ¹⁸F-FDG PET in recurrent lung cancer and to evaluate the feasibility of dose escalation boosting only regions with high FDG uptake identified on baseline PET.

Methods: Nineteen patients with stages II-IV inoperable lung cancer were selected. Volumes of interest (VOI) on pre-therapy FDG-PET were defined using an isocontour at ≥50% of SUVmax. VOI of pre- and post-therapy PET images were correlated for the extent of overlap. A highly optimized IMRT plan to 60 Gy prescribed to PTV defined on the planning CT was designed using clinical dose constraints for the organs at risk. A boost of 18 Gy was prescribed to the VOI defined on baseline PET. A composite plan of the total 78 Gy was compared with the base 60 Gy plan. Increases in dose to the lungs, spinal cord and heart were evaluated. IMRT boost plan was compared with proton RT and SBRT boost plans.

Results: Overlap fraction of baseline PET VOI with the VOI on 10 days-post therapy PET was 0.8 (95% CI: 0.7 - 0.9). Using baseline VOI as a boosting volume, dose could be escalated to 78 Gy for 15 patients without compromising the dose constraints. For 4 patients, the dose limiting factors were V20Gy and Dmean for the total lung, and Dmax for the spinal cord. An increase of the dose to OARs correlated significantly with the relative size of the boost volume.

Conclusion: VOI defined on baseline 18F-FDG PET by the SUVmax-≥50% isocontour may be a biological target volume for escalated radiation dose. Dose escalation to this volume may provide improved tumor control without breaching predefined dose constraints for OARs. The best treatment outcome may be achieved with proton RT for large targets and with SBRT for small targets.

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