Radiation and Cancer Physics

SS 32 - Physics 10 - Imaging for Response Assessment II

235 - Total Body Quantification of Active Bone Marrow Response to Chemoradiation Therapy Using FLT PET Images in Pelvic Cancer Patients

Wednesday, October 24
8:25 AM - 8:35 AM
Location: Room 217 A/B

Total Body Quantification of Active Bone Marrow Response to Chemoradiation Therapy Using FLT PET Images in Pelvic Cancer Patients
S. Kazemifar, A. Owrangi, and S. M. McGuire; University of Texas Southwestern Medical Center, Dallas, TX

Purpose/Objective(s): To quantify bone marrow radiation dose response using total body bone marrow (TBBM) quantification analysis of sequentially obtained FLT PET images prior to, during, and after chemoradiation therapy in pelvic cancer patients.

Materials/Methods: 33 pelvic cancer patients were enrolled in IRB approved protocols to obtain FLT PET images prior to, during, and after chemoradiation therapy. Pre-therapy images were used as a control for pelvic bone marrow FLT uptake change. Time series FLT PET images were acquired after 1 week (5 fractions) and 2 weeks (10 fractions) during therapy and 30 days and 1 year after therapy was complete. Weekly low dose (20 mAs) attenuation correction CTs (AC CTs) were co-registered to the FLT PET images. All FLT images were resampled according to the voxel size of the AC CT. The region of interest (ROI) was defined as 5cm above the auditory canal to 10cm below the greater trochanter using a threshold value of 300 HU on each AC CT. The resampled FLT images were used to calculate the voxel by voxel FLT uptake value as a surrogate for marrow activity. A TBBM value was calculated by summing each FLT voxel value and normalizing by the number of voxels with the ROI. The results for each subject were averaged over each time point, but all subjects did not complete all time points.

Results: TBBM voxel by voxel analysis of bone marrow activity was calculated as a single normalized value for each time point with all available subject data sets: Week 0 (N = 33), Week 1 (N = 31), Week 2 (N = 28), 30 Day (N = 26), and 1 Year (N = 18). The average TBBM activity values using the 300 HU threshold were 1626 ± 434, 1438 ± 334, 1244 ± 294, 1644 ± 341, and 1613 ± 445 for Week 0, Week 1, Week 2, 30 Day, and 1 Year time points respectively. On average, Week 1 TBBM activity was 88% of Week 0 activity and Week 2 TBBM activity was 76% of Week 0 activity. TBBM recovered to within 1% of Week 0 activity 30 days and 1 year after therapy. TBBM variation was relatively high with a coefficient of variation (CV) of 27%, 23%, 24%, 21%, and 28% for Week 0, Week 1, Week 2, 30 Day and 1 Year time points respectively, which is likely due to individual patient variation. Other HU thresholds were used to identify bone, which results in higher or lower absolute values of TBBM activity. However, the relative change was within 1% and the CV was within 5%. This indicates that identifying the boney ROI for TBBM calculation is relatively insensitive to the HU threshold value even with a low quality, low dose CT.

Conclusion: This study shows the potential of an image analysis tool that quantifies TBBM activity for pelvic cancer patients before, during, and after chemoradiation therapy. This metric accounts for both bone marrow depletion and compensatory effects. Correlating an individual patient TBBM value to systemic changes in CBCs could enable patient specific therapy that maximizes therapeutic effect while minimizing toxicity.

Author Disclosure: S. Kazemifar: None. A. Owrangi: None. S.M. McGuire: Research Grant; NIH.

Samaneh Kazemifar, PhD

Disclosure:
No relationships to disclose.

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Send Email for Samaneh Kazemifar


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