Abstract No. 554 Improving accuracy of predicted lung dosimetry in 90Y-microsphere radioembolization with 99mTc-MAA planar scintigraphy

Abstract

Standard-of-care (SOC) 90Y-microsphere radioembolization planning estimates the predicted lung shunt fractions (LSFs) and lung doses (LDs) using 99mTc-macro-aggregated albumin (MAA) planar imaging and assumes 1 kg lung mass (LM). These SIR-Spheres and TheraSphere package insert acquisition and analysis instructions generally overestimate the actual LSF, LM, and LD. The goal of this work is to provide recommendations on improved planar LSF calculation (i.e., view and contour selection and liver shine-through correction) and lung mass (LM) estimation for more accurate planar LD prediction. We compared the accuracy of planar LSFs and assumed LMs in planar LD estimations to 99mTc-MAA SPECT/CT-based LSFs, LMs, and LDs in 52 consecutive patients with hepatocellular carcinoma who underwent treatment planning for 90Y glass microsphere radioembolization. A recommended planar LD calculation (i.e., LSF and lung mass estimations) was determined by comparing the absolute errors relative to SPECT/CT-based values and categorizing the likelihood (Negligible/Possible/Likely/Definite) the planar values would impact patient care. All planar LSF and LD calculations were significantly greater than the corresponding SPECT/CT values (p ≤ 0.01, paired t-test). In general, SOC geometric mean planar LSFs had significantly larger errors (med: 0.04, max: 0.12) and more Pos/Lik/Def adverse clinical impact cases (71%) than other planar LSF calculations. These values decreased to a median 0.02, maximum 0.07, and 22% when calculating LSF using only the view with the highest abdominal counts and applying a simple liver shine-through correction. Similarly, SOC LD calculation using a reference 1 kg LM had significantly larger errors (med. 4 Gy, max. 23 Gy) and more Pos/Lik/Def adverse clinical impact cases (30%) than LD calculated with the improved LSF and patient-specific lung mass (med. 2 Gy, max. 17 Gy, 16%). We recommend predicting LD with planar imaging using: LSF calculated from the liver-shine-through-corrected total lung counts (equal to 215% the left lung counts), liver counts in only the view with the highest abdominal frame counts, and patient-specific LM from chest CT densitovolumetry.