Factors modulating 99mTc-MAA planar lung dosimetry for 90Y radioembolization

Purpose To investigate the accuracy and biases of predicted lung shunt fraction (LSF) and lung dose (LD) calculations via Tc-99m-macro-aggregated albumin (Tc-99m-MAA) planar imaging for treatment planning of Y-90-microsphere radioembolization. Methods and materials LSFs in 52 planning and LDs in 44 treatment procedures were retrospectively calculated, in consecutive radioembolization patients over a 2 year interval, using Tc-99m-MAA planar and SPECT/CT imaging. For each procedure, multiple planar LSFs and LDs were calculated using different: (1) contours, (2) views, (3) liver Tc-99m-MAA shine-through compensations, and (4) lung mass estimations. The accuracy of each planar-based LSF and LD methodology was determined by calculating the median (range) absolute difference from SPECT/CT-based LSF and LD values, which have been demonstrated in phantom and patient studies to more accurately and reliably quantify the true LSF and LD values. Results Standard-of-care LSF using geometric mean of lung and liver contours had median (range) absolute over-estimation of 4.4 percentage points (pp) (0.9 to 11.9 pp) from SPECT/CT LSF. Using anterior views only decreased LSF errors (2.4 pp median, -1.1 to +5.7 pp range). Planar LD over-estimations decreased when using single-view versus geometric-mean LSF (1.3 vs. 2.6 Gy median and 7.2 vs. 18.5 Gy maximum using 1000 g lung mass) but increased when using patient-specific versus standard-man lung mass (2.4 vs. 1.3 Gy median and 11.8 vs. 7.2 Gy maximum using single-view LSF). Conclusions Calculating planar LSF from lung and liver contours of a single view and planar LD using that same LSF and 1000 g lung mass was found to improve accuracy and minimize bias in planar lung dosimetry.

Automated summary

This study investigates the accuracy and biases of predicted lung shunt fraction (LSF) and lung dose (LD) calculations using Tc-99m-macro-aggregated albumin (Tc-99m-MAA) planar imaging for treatment planning of Y-90-microsphere radioembolization. The results suggest that calculating planar LSF from lung and liver contours of a single view and using that same LSF and 1000 g lung mass can improve accuracy and minimize bias in planar lung dosimetry.