The importance of scatter correction for the assessment of lung shunting prior to yttrium-90 radioembolization therapy (original) (raw)
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Influencing Factors of Lung Shunt Fraction in Transarterial Radioembolization Treatment
Research Square (Research Square), 2023
We aimed to evaluate the in uencing factors of lung shunt fraction(LSF) in patients who underwent transarterial radioembolization treatment. We enrolled 105 patients who had either primary or metastatic liver disease. Planar and SPECT/CT images were obtained after intraarterial injection of 99m Tc-MAA to measure LSF. Planar-based LSFs(LSF planar ), calculated as the arythmetic mean(LSF AM ) and geometric mean(LSF GM ), were compared to LSF SPECT/CT . Subgroup analyses were conducted to assess the impact of scattering and spillover effects in patients with target lesions located near lung. Both lungs were segmented into lower, middle and upper sections(RL,RM,RU,LL,LM,LU). For control group, ten patients with normal lung perfusion scintigraphy were included. The mean of LSF SPECT/CT was signi cantly lower than the mean of LSF GM (6.5 ± 4.1 vs 13.9 ± 8.4, p = < 0.001) and the mean of LSF AM (13.5 ± 8.4%, p = < 0.001). LSF planar methods overestimated LSF compared to LSF SPECT/CT . LSF GM divided by 2.3 can provide more accurate estimated LSF similar to LSF SPECT/CT . In subgroup analyses, we found that mean values of RL/RU, RM/RU, LL/LU and LM/LU were 9.3 ± 7.4, 2.2 ± 1.2; 1.2 ± 0.4, and 1.2 ± 0.2, respectively. In control group, mean values of RL/RU, RM/RU, LL/LU and LM/LU were within a range of 0.9-1.1. LSF SPECT/CT with attenuation correction can provide more accurate results compared to LSF planar before TARE treatment. In patients who had liver lesions located adjacent to lung, the possible miscalculation of LSF SPECT/CT from scattering and spillover effect could be eliminated by exclusion of 3 cm diameter from inferior border of the right lung.
Quantifying lung shunting during planning for radio-embolization
Physics in Medicine and Biology, 2011
A method is proposed for accurate quantification of lung uptake during shunt studies for liver cancer patients undergoing radio-embolization. The current standard for analysis of [ 99m Tc]-MAA shunt studies is subjective and highly variable. The technique proposed in this work involves a small additional peripheral intravenous injection of macroaggregated albumin (MAA) and two additional static acquisitions (before and after injection) to quantify the absolute activity in the lungs as a result of arterio-venous shunting. Such quantification also allows for estimates of absorbed dose to lung tissue at the time of treatment based on MIRD formalism. The method was used on six radio-embolization patients attending the department for lung shunt analysis. Quantitative values for each were compared to a previously validated technique using fully quantitative SPECT/CT imaging, treated as the gold standard. The average difference between absolute activity shunted to the lungs calculated by the proposed technique compared to the previously validated technique was found to be 2%, with a range of (1-8)%. The proposed method is simple and fast, allowing for accurate quantification of lung shunting and estimates of absorbed dose to lung tissue at treatment, and may one day be used in a one-stop procedure for planning and therapy in a single interventional procedure.
EJNMMI Research, 2021
Background 99mTc-macroaggregated albumin (99mTc-MAA) scintigraphy is utilized in treatment planning for Yttrium-90 (90Y) Selective Internal Radiation Therapy (SIRT) of liver tumors to evaluate hepatopulmonary shunting by calculating the lung shunt fraction (LSF). The purpose of this study was to evaluate if LSF calculation using SPECT/CT instead of planar gamma camera imaging is more accurate and if this can potentially lead to more effective treatment planning of hepatic lesions while avoiding excessive pulmonary irradiation. Results LSF calculation was obtained using two different methodologies in 85 cases from consecutive patients intended to receive 90Y SIRT. The first method was based on planar gamma camera imaging in the anterior and posterior views with geometric mean calculation of the LSF from regions of interest of the liver and lungs. The second method was based on segmentation of the liver and lungs from SPECT/CT images of the thorax and abdomen. The differences in plana...
Medical Physics, 2019
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: (1) estimate liver counts from the MAA SPECT/CT liver contour; (2) 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; (3) compute LSF new from liver and lung counts; (4) 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.
Tomography
There is no noninvasive method to estimate lung shunting fraction (LSF) in patients with liver tumors undergoing Yttrium-90 (Y90) therapy. We propose to predict LSF from noninvasive dynamic contrast enhanced (DCE) MRI using perfusion quantification. Two perfusion quantification methods were used to process DCE MRI in 25 liver tumor patients: Kety’s tracer kinetic modeling with a delay-fitted global arterial input function (AIF) and quantitative transport mapping (QTM) based on the inversion of transport equation using spatial deconvolution without AIF. LSF was measured on SPECT following Tc-99m macroaggregated albumin (MAA) administration via hepatic arterial catheter. The patient cohort was partitioned into a low-risk group (LSF ≤ 10%) and a high-risk group (LSF > 10%). Results: In this patient cohort, LSF was positively correlated with QTM velocity |u| (r = 0.61, F = 14.0363, p = 0.0021), and no significant correlation was observed with Kety’s parameters, tumor volume, patient ...
Lung Shunt Dose With A Planar Versus Spect-CT Images In Planification Of HCC Treatment
2021
PURPOSE: The purpose is to investigate the possibility of evaluate the lung shunt fraction LSF with SPECT image in planning with Tc-99m of hepatic HCC treatments with Y-90 microspheres, comparing the results with those obtained with planar images. METHODS: Firstly, for a patient with a predictably high shunt, the 4 planar images are used as in the classic method to determine PLANAR LSF. Second, to determine the SPECT LSF, the SPECT images acquired for planning the therapeutic activity, and therefore centered in the hepatic region, are used. These images does not cover the entire lung but only some slices. Advantage is taken of the fact that the distribution of 99MTc in healthy lung tissue is homogeneous. Then the activity concentration in the lung can be known and the SPECT LSF can be calculated. RESULTS: The values obtained for PLANAR LSF and SPECT LSF are 11% and 28%, respectively. The results for the lung dose Dlung are of 24.50 Gy and 7.92 Gy, respectively. CONCLUSION: In this...
EJNMMI research, 2014
For yttrium-90 ((90)Y) radioembolization, the common practice of assuming a standard 1,000-g lung mass for predictive dosimetry is fundamentally incongruent with the modern philosophy of personalized medicine. We recently developed a technique of personalized predictive lung dosimetry using technetium-99m ((99m)Tc) macroaggregated albumin (MAA) single photon emission computed tomography with integrated CT (SPECT/CT) of the lung as part of our routine dosimetric protocol for (90)Y radioembolization. Its rationales are the technical superiority of SPECT/CT over planar scintigraphy, ease and convenience of lung auto-segmentation CT densitovolumetry, and dosimetric advantage of patient-specific lung parenchyma masses. This is a retrospective study of our pulmonary clinical outcomes and comparison of lung dosimetric accuracy and precision by (99m)Tc MAA SPECT/CT versus conventional planar methodology. (90)Y resin microspheres (SIR-Spheres) were used for radioembolization. Diagnostic CT d...
Scatter imaging during lung stereotactic body radiation therapy characterized with phantom studies
Physics in Medicine & Biology, 2020
By collecting photons scattered out of the therapy beam, scatter imaging creates images of the treated volume. Two phantoms were used to assess the possible application of scatter imaging for markerless tracking of lung tumors during stereotactic body radiation therapy (SBRT) treatment. A scatter-imaging camera was assembled with a CsI flat-panel detector and a 5 mm diameter pinhole collimator. Scatter images were collected during the irradiation of phantoms with megavoltage photons. To assess scatter image quality, spherical phantom lung tumors of 2.1-2.8 cm diameters were placed inside a static, anthropomorphic phantom. To show the efficacy of the technique with a moving target (3 cm diameter), the position of a simulated tumor was tracked in scatter images during sinusoidal motion (15 mm amplitude, 0.25 Hz frequency) in a dynamic lung phantom in open-field, dynamic conformal arc (DCA), and volumetric modulated arc therapy (VMAT) deliveries. Anatomical features are identifiable on static phantom scatter images collected with 10 MU of delivered dose (2.1 cm diameter lung tumor contrast-to-noise ratio of 4.4). The contrast-tonoise ratio increases with tumor size and delivered dose. During dynamic motion, the position of the 3.0 cm diameter lung tumor was identified with a root-mean-square error of 0.8, 1.2, and 2.9 mm for open field (0.3 s frame integration), DCA (0.5 s), and VMAT (0.5 s), respectively. Based on phantom studies, scatter imaging is a potential technique for markerless lung tumor tracking during SBRT without additional imaging dose. Quality scatter images may be collected at low, clinically relevant doses (10 MU). Scatter images are capable of sub-millimeter tracking precision, but modulation decreases accuracy.
Radiotherapy and Oncology, 1995
Purpose: To determine the accuracy of dose calculations based on CT-densities for lung cancer patients irradiated with an anterioposterior parallel-opposed treatment technique and to evaluate, for this technique, the use of diodes and an Electronic Portal Imaging Device (EPID) for absolute exit dose and relative transmission dose verification, respectively. Materials and methodr: Dose calculations were performed using a 3-dimensional treatment planning system, using CT-densities or assuming the patient to be water-equivalent. A simple inhomogeneity correction model was used to take CT-densities into account. For 22 patients, entrance and exit dose calculations at the central beam axis and at several off-axis positions were compared with diode measurements. For 12 patients, diode exit dose measurements and exit dose calculations were compared with EPID transmission dose values. Results: Using water-equivalent calculations, the actual exit dose value under lung was, on average, underestimated by 30%, with an overall spread of 10% (1 SD) in the ratio of measurement and calculation. Using inhomogeneity corrections, the exit dose was, on average, overestimated by 4%, with an overall spread of 6% (1 SD). Only 2% of the average deviation was due to the inhomogeneity correction model. The other 2% resulted from a small inaccuracy in beam fit parameters and the fact that lack of backscatter is not taken into account by the calculation model. Organ motion, resulting from the ventilatory or cardiac cycle, caused an estimated uncertainty in calculated exit dose of 2.5% (1 SD). The most important reason for the large overall spread was, however, the inaccuracy involved in point measurements, of about 4% (1 SD), which resulted from the systematic and random deviation in patient setup and therefore in the diode position with respect to patient anatomy. Transmission and exit dose values agreed with an average difference of 1.1%. Transmission dose profiles also showed good agreement with calculated exit dose profiles. Conclusions: The study shows that, for this treatment technique, the dose in the thorax region is quite accurately predicted using CT-based dose calculations and a simple heterogeneity correction model. Point detectors such as diodes are not suitable for exit dose verification in regions with inhomogeneities. The EPID has the advantage that the dose can be measured in the entire irradiation field, thus allowing an accurate verification of the dose delivered to regions with large dose gradients.
Journal of nuclear medicine : official publication, Society of Nuclear Medicine, 2016
Perfusion scintigraphy (PS) using technetium-99m ((99m)Tc) labeled albumin-aggregates is a mandatory step before hepatic radioembolization (RE) with yttrium-90-labeled microspheres. Within the bounds of a prospective clinical trial, this sub-analysis assessed the intrahepatic and intrapulmonary stability of two albumin-compounds, (99m)Tc-MAA (macroaggregated serum albumin, MAA) and (99m)Tc-HSA (human serum albumin, HSA) after intra-arterial injection. In n = 24 patients (age: 64.6y: 46.2-82.2) with metastatic colorectal cancer (mCRC), PS-data of both tracers were analyzed (n = 12 patients each). Biodistribution (liver, lung) and liver-lung shunt (LLS) was assessed by sequential planar scintigraphy (1h, 5h and 24h post intra-hepatic/intra-arterial injection; p.i.) using the region of interest (ROI) technique. Data were corrected for radioactive decay. Liver uptake of MAA decreased significantly from 1h (median particle uptake=70.0%) to 5h (45.5%, p<0.0001) and 24h (27.9%, p<0.0...