Program Information
Effect of 90Y SPECT/CT Self-Calibration Approaches On Absorbed Dose Quantification Following 90Y-Microsphere Selective Internal Radiation Therapy (90Y-SIRT)
A Balagopal*, S Kappadath, UT MD Anderson Cancer Center, Houston, TX
Presentations
WE-F-201-8 (Wednesday, August 2, 2017) 1:45 PM - 3:45 PM Room: 201
Purpose: 90Y-SIRT is unique that the total 90Y activity inside the liver can be determined with an uncertainty <5-10%; hence post-therapy 90Y-SPECT/CT images can be quantified via self-calibration. There is no established method for 90Y-SPECT self-calibration and its effects on dose quantification is unknown. This study investigates the effect of different 90Y-SPECT self-calibration approaches on quantification of voxel absorbed doses following 90Y-SIRT.
Methods: SPECT/CT images of 31 patients (48 tumors) following 90Y-SIRT were contoured by radiologist. 90Y-SPECT images [counts/ml] were converted to activity concentration [Bq/ml] using MIM 90Y-SurePlan commercial software to investigate the following VOI prescriptions for SPECT self-calibration: SPECT field-of-view (SFOV), total body (thorax and abdomen, TB), total liver (TL), total liver expanded by 1 pixel or 5mm (TL+5mm), total liver contracted by 5mm (TL-5mm). The 90Y-SurePlan tool was validated using DOSXYZnrc Monte Carlo based radiation transport. The different approaches for self-calibration were analyzed using linear correlation and Bland-Altman analysis.
Results: The mean dose with SFOV calculated using 90Y-SurePlan was <3% of Monte Carlo for tumors and normal livers; values changed slightly for other DVH metrics. Tumor mean dose calculated using TB, TL, TL+5mm, TL-5mm self-calibration VOIs were within 2%, 68%, 47%, and 107% of SFOV; the corresponding values for normal liver mean doses were within 1.3%, 73%, 50%, and 114%. Self-calibration with TB was equivalent to SFOV; but self-calibration with TL yielded substantially higher (~70%) dose values. Assuming that SPECT counts outside liver arise from incomplete scatter correction, self-calibration using TL may be more accurate; however, it is less precise as 1pixel (5mm) contour variability introduces large (~20%) changes in dose.
Conclusion: The accuracy of 90Y-SurePlan dosimetry relative to Monte Carlo was clinically acceptable. The large biases in dose with self-calibration VOIs discovered by this study suggests that consistent dose calculation approaches are essential when comparing 90Y-SIRT dosimetry.
Funding Support, Disclosures, and Conflict of Interest: SCK: Research support from GE; Consultant for BTG
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