Program Information

Variation in Dynamic Positron Emission Tomography Imaging of Tumor Hypoxia in Early Stage Non-Small Cell Lung Cancer Patients Undergoing Stereotactic Body Radiotherapy

O Kelada^1,2*, R Decker¹ , M Zheng³ , Y Huang³ , Y Xia³ , J Gallezot³ , C Liu³ , S Rockwell¹ , R Carson³ , U Oelfke² , D Carlson¹ , (1) Department of Therapeutic Radiology, Yale University School of Medicine, New Haven, Connecticut, (2) Department of Medical Physics in Radiation Oncology, German Cancer Research Center, Heidelberg, Germany, (3) Department of Diagnostic Radiology, Yale University School of Medicine, New Haven, Connecticut

Presentations

WE-G-BRD-6 Wednesday 4:30PM - 6:00PM Room: Ballroom D

Purpose:
Tumor hypoxia is correlated with treatment failure. To date, there are no published studies investigating hypoxia in non-small cell lung cancer (NSCLC) patients undergoing SBRT. We aim to use 18F-fluoromisonidazole (18F-FMISO) positron emission tomography (PET) imaging to non-invasively quantify the tumor hypoxic volume (HV), to elucidate potential roles of reoxygenation and tumor vascular response at high doses, and to identify an optimal prognostic imaging time-point.

Methods:
SBRT-eligible patients with NSCLC tumors >1cm were prospectively enrolled in an IRB-approved study. Computed Tomography and dynamic PET images (0-120min, 150-180min, and 210-240min post-injection) were acquired using a Siemens BiographmCT PET/CT scanner. 18F-FMISO PET was performed on a single patient at 3 different time points around a single SBRT delivery of 18 Gy and HVs were compared using a tumor-to-blood ratio (TBR)>1.2 and rate of influx (Ki)>0.0015 (Patlak).

Results:
Results from our first patient showed substantial temporal changes in HV following SBRT. Using a TBR threshold >1.2 and summed images 210-240min, the HVs were 19%, 31% and 13% of total tumor volume on day 0, 2 (48 hours post-SBRT), and 4 (96 hours post-SBRT). The absolute volume of hypoxia increased by nearly a factor of 2 after 18 Gy and then decreased almost to baseline 96 hours later. Selected imaging timepoints resulted in temporal changes in HV quantification obtained with TBR. Ki, calculated using 4-hour dynamic data, evaluated HVs as 22%, 75% and 21%, respectively.

Conclusions:
With the results of only one patient, this novel pilot study highlights the potential benefit of 18F-FMISO PET imaging as results indicate substantial temporal changes in tumor HV post-SBRT. Analysis suggests that TBR is not a robust parameter for accurate HV quantification and heavily influenced by imaging timepoint selection. Kinetic modeling parameters are more sensitive and may aid in future treatment individualization based on patient-specific biological information.

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