Effect of predicted lung mass versus fixed mass regimes on lung dose in SIRT (90Y)

Abstract

This work sought to investigate the impact of fixed lung mass regime versus individualized measures on the lung absorbed dose in 90Y therapy. 14 patients were injected with 3-5 mCi 99mTc-MAA pursued by whole-body scans with 15% photo-peak window width at 140 keV. SPECT/CT scans were acquired with attenuation and scatter correction. The lung shunt fraction (LSF) was generated from whole-body scans (WBS) and SPECT/CT. Lung volume was measured by contouring the target organ over CT images. Variation, Kruskal Wallis, and Mann-Whitney tests were applied for statistical analysis. In result, 64% of the patients exhibited less than 1 kg lung mass, and the remaining 26% had lung mass larger than 1 kg. The estimated lung shunt fractions from SPECT/CT were greatly lower than planar images with a median of -45% (range: -28 to -69%). The lung dose estimates varied between fixed lung-mass regime used in (TheraSphere Treatment Sheet) and real measures approach with a median difference of 9% and a range from -34% to 76%. However, a significant difference was found in lung dose estimates between planar and SPECT/CT modalities independent of lung mass. It was accordingly inferred that lung mass may vary among patients influencing the predicted dose and the tailored 90Y activity. For precise medicine, the fixed lung mass used on a routine basis should be replaced by patient-specific measures.