(Sunday, 7/12/2020) [Eastern Time (GMT-4)]
Room: AAPM ePoster Library
Purpose: Predicted lung-shunt fraction (LSF) and lung dose (LD) via standard-of-care 99mTc-macro-aggregated albumin (99mTc-MAA) planar imaging can vary depending on the views acquired, contours drawn, and lung mass assumed. Our goal is to provide practical recommendations to more accurately estimate LSF and LD with planar scintigraphy.
Methods: In 46 patients that underwent 99mTc-MAA planar and SPECT/CT imaging for treatment planning, we retrospectively calculated multiple planar LSF estimates using contours drawn on different views with and without compensation of liver 99mTc-MAA shine-through in the lung contours. Accuracy of planar LSFs was assessed by calculating absolute differences from gold-standard SPECT/CT-based LSF and by quantifying percentage of cases where the over-estimated planar LSF might have unnecessarily prevented administering the desired 90Y-microsphere tumor dose. In 44 cases that proceeded to therapy, we calculated multiple planar LD estimates using either standard-of-care geometric-mean or more accurate (determined above) planar LSFs and either 1000g or patient-specific CT-based lung masses. Accuracy of planar LDs was assessed by calculating absolute differences from SPECT/CT-based LD.
Results: Standard-of-care LSF from the geometric mean of lung and liver contours had median (95%range) over-estimation of 0.045 (0.012-0.059) from SPECT/CT LSF. Our recommended LSF using lung and liver contours on the anterior view decreased this over-estimation to 0.028 (0.003-0.044) and reduced the cases that might not have been prescribed the desired 90Y-microsphere tumor dose from 27% to 12%. Median (95%range) patient specific lung masses were 816g (548-1172g). Planar LD over-estimations decreased when using recommended vs. standard-of-care planar LSFs (1.7Gy/9.7Gy vs. 3.6Gy/18.5Gy median/maximum using 1000g lung mass) but increased when using patient-specific vs. 1000g lung mass (2.6Gy/14.7Gy vs. 1.7Gy/9.7Gy median/maximum with recommended LSF).
Conclusion: We recommend calculating planar LSF using lung and liver contours of a single view instead of geometric means of both views (standard-of-care) and calculating planar LD using standard-man 1000g lung mass.
Funding Support, Disclosures, and Conflict of Interest: Work supported in part by UT MDACC Support Grant CA016672. SCK serves as consultant for Boston Scientific, Sirtex, ABK Biomedical, Varian Medical. AM serves as consultant for Boston Scientific, Sirtex, ABK Biomedical.
Keywords
Targeted Radiotherapy, Treatment Planning, Planar Imaging
Taxonomy
IM/TH- Radiopharmaceutical Therapy: Dose estimation: MIRD/deterministic
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