Abstract
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Objectives: Selective Internal Radiation Therapy (SIRT) is a widely used radioembolization procedure performed on patients with unresectable primary or metastatic hepatic malignancy(1).Radiation pneumonitis is a rare complication which can occur when certain microspheres inadvertently shunt to the lung parenchyma (2).Prior to SIRT,lung shunt fraction(LSF) estimation is generally performed using Tc-99m-Macroaggregated (MAA) whole body planar scintigraphy. However, several studies have suggested drawbacks with this approach(3,4).The aim of this study was to investigate the application of SPECT/CT for quantitative assessment of LSF.
Methods: A retrospective study was performed in patients undergoing SIRT. Planar scintigraphy images were acquired in anterior and posterior views from which the LSF was determined. For SPECT-based lung shunt analysis, the lungs and liver were delineated based on the low-dose CT and co-registered to the SPECT. Reconstructed images were corrected for scatter attenuation and resolution recovery. The SPECT/CT system used is Philips Bright view XCT with Astonish SPECT reconstruction software. To validate SPECT/CT LSF quantification in an anthropomorphic torso phantom with a simulated 9.9% LSF was imaged on both planar and SPECT/CT.
Results: Fifty patients were included in the study. Based on planar MAA scans, LSF was calculated at a median of 7 % (range: 1.1-32.6 %),while quantitation of SPECT/CT's yielded only 3.2% (range 1.3-21.2%). Overall, 94% of patients had overestimation of planar scintigraphy derived LSF, ranging from 0.1-4 times the SPECT/CT-based LSF estimation. Only, 2/50 patients had higher LSF values using SPECT/CT approach. One patient had similar results by using either methodology. SPECT re-registration was necessary in 38/50 patients. For the anthropomorphic phantom, the LSF from planar images was 18.5%, whereas for SPECT it was 9.5%
Conclusions: By comparing planar scintigraphy and SPECT/CT, our data highlights the overestimation of LSF using conventional planar scans. The ability of SPECT/ CT to correct for scatter and attenuation along with 3D image acquisition can provide more accurate quantitative assessment of LSF, thereby more accurately determining the lung radiation dose.