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Calculation of lung mean dose and quantification of error for 90 Y‐microsphere radioembolization using 99m Tc‐MAA SPECT/CT and diagnostic chest CT
Author(s) -
Lopez Benjamin,
Mahvash Armeen,
Lam Marnix G. E. H.,
Kappadath S. Cheenu
Publication year - 2019
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1002/mp.13575
Subject(s) - nuclear medicine , microsphere , dosimetry , medical imaging , medicine , physics , radiology , chemical engineering , engineering
Purpose Current treatment planning for 90 Y radioembolization estimates lung mean dose (LMD) by measuring the lung shunt fraction (LSF) from 99m Tc‐macroaggregated albumin (MAA) planar imaging and assuming a 1‐kg lung mass. This methodology, however, overestimates LSF and LMD and could therefore unnecessarily limit the dose to target volume(s). We propose an improved LMD calculation that derives LSF from 99m Tc‐MAA SPECT/CT and the patient‐specific lung mass from diagnostic chest CT. Furthermore, we investigated the errors in lung mass, LSF, and LMD arising from contour variability in patient data in order to estimate the precision of our proposed methodology. Methods Our proposed LMD (LMD new ) calculation consisted of the following steps: (a) estimate liver counts from the MAA SPECT/CT liver contour; (b) estimate total lung counts by multiplying density (counts/g) from the MAA SPECT/CT left‐lung contour by the total lung mass (g) from the diagnostic CT lung contours; (c) compute LSF new from liver and lung counts; (d) calculate LMD new using LSF new and the total lung mass from the diagnostic CT (M new ). LMD new , LSF new , and M new estimates were compared to standard model values (LMD clin , LSF clin , and 1 kg, respectively) in 52 consecutive patients with hepatocellular carcinoma who underwent radioembolization using 90 Y glass microspheres. The precision of our methodology was quantified by varying lung and liver contours in the same patient population and calculating the resulting relative errors in the liver count, lung count, and lung mass measurements. Results The median M new was 839 g (range, 550–1178 g) for men and 731 g (range, 548–869 g) for women. The median LSF new was 0.02 (range, 0.01–0.11), while the median LMD new was 4.9 Gy (range, 0.3–25.5 Gy). M new , LSF new , and LMD new were significantly lower than M clin , LSF clin , and LMD clin , with respective relative mean (±SD) differences of −20% (±16%) for M new , −63% (±15%) for LSF new , and −53% (±23%) for LMD new . The estimated 1‐sigma uncertainties in M new , LSF new , and LMD new were 9%, 10%, and 13%, respectively. Conclusions We derived a method to calculate lung mass and LSF using routinely available diagnostic chest CT and 99m Tc‐MAA SPECT/CT. More importantly, we systematically quantified the errors in our measurements to establish the precision of the estimated lung dose (13%). The proposed methodology provides a more accurate LMD and an estimate of its precision, which will improve treatment and retreatment planning for 90 Y radioembolizations.