2815 - Workflow and Treatment Volumes for UMCC2023.006: A Pilot Phase II Trial of Individualized FDG-PET and DCE-MRI Directed Adaptive RT in HPV-related Stage III Oropharynx Cancer (OPSCC)
Presenter(s)
B. Nasser1, B. S. Rosen1, M. P. Aryal1, Y. Cao2, J. Balter1, N. D'Silva3, P. L. Swiecicki4, F. Worden4, J. L. Shah1, and M. L. Mierzwa5; 1Department of Radiation Oncology, University of Michigan, Ann Arbor, MI, 2Departments of Radiology and Biomedical Engineering, University of Michigan, Ann Arbor, MI, 3University of Michigan, Ann Arbor, MI, United States, 4Department of Internal Medicine, Division of Hematology/Oncology, University of Michigan, Ann Arbor, MI, 5Rogel Cancer Center, University of Michigan, Ann Arbor, MI
Purpose/Objective(s): We have previously demonstrated improved locoregional control in locally advanced p16+ OPSCC using an adaptive physiologic MRI boost in locally advanced poor prognosis head and neck cancer. Here, we conducted a pilot study of adaptive RT boost that incorporates midtreatment persistently FDG-avid as well as persistently low blood volume (LBV) tumor subvolumes (TV) on FDG-PET and DCE-MRI respectively.
Materials/Methods: Eligibility included AJCC 8 stage III p16+ OPSCC planned for definitive chemoradiation, ECOG 0-2, with concurrent weekly cisplatin 40mg/m2 or carboplatin (AUC=2) for cisplatin ineligibility. All patients started with RT plan to deliver 70Gy to PTVhigh and 56Gy to PTVlow in 35 fractions. FDG-PET and DCE-MRI were acquired at baseline, and at fraction 10. A second mid-treatment FDG-PET was acquired at fraction 20. Low BV and SUV maps were created within GTV in imFIAT and transferred to patient information system. The first boost volume (GTVboost1) was a spatial union of the persisting LBV subvolume (LBV_overlap) and the persistent FDG-avid subvolume with SUV>3 (MTV3_2wk). GTVboost1 + 3mm=PTVboost1. PTVboost1 received 2.5Gy/day starting with fraction 15. A second mid-treatment FDG-PET was acquired at fraction 20. Tumor subvolumes of persistent SUV>3 plus LBVoverlap made up GTVboost2 and continued boost at 2.5Gy/fraction starting with fraction 23. Any persistent tumor subvolume >1cc volume received boost with dose constraint of D0.01cc <70Gy for mucosa, mandible or hyoid. Total boost dose was 80Gy (86Gy EQD2).
Results: 17 patients have completed RT boost. Most had cT4 disease (94%), primarily white males (100%) with 6/17 (35%) with >10 pack year smoking history. At baseline, the median primary tumor volume (GTVp) was 38.5 cc and nodal tumor volume (GTVn) was 26.7 cc. TV with SUV>3 was 25.9 cc for primary tumor and 1.1 cc for nodal subvolume, and LBV TV was 12.4 cc for primary tumor and 1.9 cc for nodal subvolume. The median overlap between baseline SUV>3 and LBV TVs was 2.511 cc for primary tumor and 0 cc for node volume. At fraction 10, the median MTV3_2k was 19.1cc and 0.1 cc for node subvolume, and the LBV_overlap was 6.4cc for primary tumor and 1.8cc for node subvolume. The overlap between SUV and LBV subvolumes was 0.007cc for primary tumor and 0 cc for nodes. At fraction 20, the median persistent MTV3_4wk was 7.8cc for primary tumor and 0cc for nodes. 9/17 (53%) patients received RT boost to 80Gy, with the GTV subvolume receiving 80Gy in the primary tumor was 8.345 cc, with 0 cc in GTVn.
Conclusion: Adaptive MRI and FDG-PET guided radiation boost is feasible in oropharynx cancer. The RT boost to 80Gy representing 21.69% of GTVp and 0% of GTVn. At baseline and fraction 10, we saw very little overlap of FDG-avid and low blood volume TVs in the GTVp with essentially no overlap in GTVn.