Fiducial visibility on planar images during motion-synchronized tomotherapy treatments

Objective: Synchrony® is a motion management system on the Radixact® that uses planar kV radiographs to locate the target during treatment. The purpose of this work is to quantify the visibility of fiducials on these radiographs. Approach: A custom acrylic slab was machined to hold 8 gold fiducials of various lengths, diameters, and orientations with respect to imaging axis. The slab was placed on the couch at the imaging isocenter and planar radiographs were acquired perpendicular to the custom slab with varying thicknesses of acrylic on each side. Fiducial signal to noise ratio (SNR) and detected fiducial position error in millimeters were quantified. Main Results: The minimum output protocol (100 kVp, 0.8 mAs) was sufficient to detect all fiducials on both Radixact configurations when the thickness of the phantom was 20 cm. However, no fiducials for any protocol were detected when the phantom was 50 cm thick. The algorithm accurately detected fiducials on the image when the SNR was larger than 4. The MV beam was observed to cause RFI artifacts on the kV images and to decrease SNR by an average of 10%. Significance: This work provides the first data on fiducial visibility on kV radiographs from Radixact Synchrony treatments. The Synchrony fiducial detection algorithm was determined to be very accurate when sufficient SNR is achieved. However, a higher output protocol may need to be added for use with larger patients. This work provided groundwork for investigating visibility of fiducial-free solid targets in future studies and provided a direct comparison of fiducial visibility on the two Radixact configurations, which will allow for intercomparison of results between configurations.

Usefulness of 99mTc–pertechnetate SPECT-CT in thyroid tissue volumetry: phantom studies and a clinical case series

Background: An accurate measurement of the target volume is of primary importance in theragnostics of hyperthyroidism Objective: Our purpose was to evaluate the accuracy of a threshold–based isocontour extraction procedure for thyroid tissue volumetry from SPECT-CT. Methods: Cylindrical vials with a fixed volume of 99mTcO4 at different activities were inserted into a neck phantom in two different thickness settings. Images were acquired by orienting the phantom in different positions, i.e., 40 planar images and 40 SPECT-CT. The fixed values of the iso-contouring threshold for SPECT and SPECT-CT were calculated by means of linear and spline regression models. Mean, Median, Standard Deviation, Standard Error, Mean Absolute Percentage Error and Root Mean-Square Error were computed. Any difference between the planar method, SPECT and SPECT-CT and the effective volume was evaluated by means of ANOVA and post-hoc tests. Moreover, planar and SPECT-CT acquisitions were performed in 8 patients with hyperthyroidism, considering relevant percentage differences greater than > 20 % from CT gold standard. Results: Concerning phantom studies, the planar method shows higher values of each parameter than the other two methods. SPECT-CT shows lower variability. However, no significant differences were observed between SPECT and SPECT-CT measurements. In patients, relevant differences were found in 7 out of 9 lesions with the planar method, in 6 lesions with SPECT, but in only one with SPECT-CT. Conclution: Our study confirms the superiority of SPECT in volume measurement if compared with the planar method. A more accurate measurement can be obtained from SPECT-CT.

Pitfalls of the Semi-Quantitative Analyzing 99mTc-Pyrophosphate Planar Images for Diagnosing Transthyretin Cardiac Amyloidosis: A Possible Solution

Background: Two different approaches, 1-h heart-to-contralateral (H/CL) ratio and 3-h visual grading scale relative to ribs (VGSr), have been established to interpret 99mTc-PYP planar images for the detection of amyloid transthyretin cardiac amyloidosis (ATTR-CA). Since they are prone to pitfalls, this pilot study aimed to explore the diagnostic practicality of the 3-h visual grading scale relative to the upper segment of sternum (VGSs) approach for interpreting 99mTc-PYP planar images. Methods: A total of 42 patients were enrolled in this retrospective study. SPECT/CT approach and planar approaches including H/CL ratio, VGSr, and VGSs were utilized to interpret the 99mTc-PYP images obtained at both 1 and 3 h. The classification criteria of the latest expert consensus recommendations were considered as the gold standard. The concordance between the interpretation of each approach and the gold standard was investigated. Results: In addition to 1- and 3-h SPECT/CT approaches, the interpretation of planar images using the 3-h VGSs approach was also applicable, which turns identical to the gold standard (κ = 1.000; p < 0.001). Conclusions: For the interpretation of 99mTc-PYP planar images, the 3-h VGSs approach should be the optimal method, particularly in the case without available or feasible tomography imaging. Only one imaging session (planar and SPECT/CT) at 3 h would be sufficient for the detection of ATTR-CA, and favorable for patient satisfaction.

373 Utility of the early phase of DPD scintigraphy in the diagnosis of correlated TT-R cardiac amyloidosis

Aims The importance of cardiac scan with phosphonate-based radiotracers in the diagnosis of cardiac amyloidosis is now well established. Standard imaging is performed 3 h after tracer injection with a planar view on the cardiac region. This study sought to evaluate the predictive role of early-phase myocardial uptake (10 min after injection) of 99mTc-3,3-diphosphono-1,2-propanodicarboxylic acid (DPD) compared compared with standard late acquisition, in patients with suspected hereditary transthyretin-related cardiac amyloidosis (TTR-CA). Methods and results Fifty five patients with suspected of TTR-CA with typical aspects of the relative apical sparing at two-dimensional speckle-tracking echocardiography, reported as a specific pattern for cardiac amyloidosis, were enrolled after having signed informed written consent. They have been subjected to a 99mTc-DPD cardiac scintigraphy with planar acquisition at 10 min and 3 h after tracer injection (13 Mbq/Kg). Patients with cardiac uptake on the planar images concluded the examination with a SPECT-CT (cardiac protocol) to assess the affected myocardial segments. On planar images the heart-to-mediastinum-ratio was measured. Subsequently, the diagnosis of amyloidosis has to be confirmed with morphologic examinations such as biopsy and genetic tests. Of the enrolled patients with clinical and echocardiographic aspect of TTR-CA, 22 were positive for cardiac amyloidosis. All of them showed tracer uptake in both early and late images. In patients with positive results, the early-phase showed a Heart-to-mediastinum-ratio &gt;1.2. SPECT/CT showed involvement of almost two myocardial segments: in all patients the ventricular septum showed significant tracer uptake. Conclusions Our small group of patients showed that 99mTc-DPD myocardial uptake intensity on early-phase scintigraphy can be used to anticipate the results of late images in diagnosis of TTR cardiac amyloidosis.

Quantification of Tc-99m macroaggregated albumin liver perfusion as a predictor of tumor response to intra-arterial therapy with yttrium 90 spheres

Objectives: It remains unclear whether quantifying the pre-therapy tumor Technetium 99m macro aggregated albumin (Tc 99m MAA) localization can accurately predict the response to Yttrium 90 (Y-90) spheres therapy. Present studies are limited and with contradictory results. The aim of this study is to determine if quantification of Tc-99m MAA in hepatic tumor lesion(s) on pretherapy planning nuclear scan can predict the degree of tumor response after radioembolization using Y-90 Spheres. Material and Methods: We retrospectively included patients with primary liver cancers or metastases who were treated with SirSpheres or TheraSpheres. All patients had a Tc-99m MAA scan with an average dose of 5.0mCi injected aseptically in either the right, left, or common hepatic artery. The patients were subsequently transferred for imaging using planar and single-photon emission computed tomography (SPECT) of the abdomen and planar images of the chest. We calculated geometric mean of radiotracer counts in the largest lesion in the lobe to be treated by placing same size region of interest (ROI) around the largest lesion on the anterior and posterior planar images. Subsequently, an irregular ROI around the liver or lobe to be treated were drawn to calculate the geometric mean of counts in the liver. The percent tracer accumulation in the largest lesion was calculated by dividing the geometric mean of counts in the largest lesion by the geometric mean of counts in the liver or lobe and multiplying by 100%. The size of this largest lesion was obtained on the most recent CT or magnetic resonance imaging (MRI) in cm in 2 directions prior to treatment with Y-90 Spheres. The extent of the response to Y-90 Spheres therapy was re-evaluated with 3 months follow-up MRI or CT by measuring the decrease in the largest lesion size. Comparison of the percent Tc-99 MAA count accumulation in the largest lesion on the pre-therapy scan with the reduction in size using anatomic imaging was performed. Results: A total of 30 patients were included (16 hepatocellular carcinoma, eight colorectal, three breast, one neuroendocrine, one cholangiocarcinoma, and one cervical metastases). There were 14 patients in stable disease or progressive disease group (SD/PD gp) and 16 patients in partial response or complete response group (PR/CR gp). The median lesion size was 3.5 cm in the PD/SD gp versus 2.8 cm in the PR/CR gp (P = 0.31). Additionally, the median delivered Y90 Spheres treatment dose was 51.3 mCi in the PD/SD versus 43.2 mCi in the PR/CR gp (P = 0.22). The percent median largest lesion to liver concentration was 21.9% in the PR/CR gp versus 23.3% in the PR/CR gp (P = 0.74). There was no significant difference in percent Tc-99m MAA distribution in the largest liver lesion between the SD/PD gp and the PR/CR gp. Conclusion: The degree of Tc-99m MAA localization in the largest tumor lesion in the liver compared to the remainder of the liver as quantified from planar images does not predict the response to Y-90 spheres therapy.

Comparison between planar and single-photon computed tomography images for radiation intensity quantification in iodine-131 scintigraphy

This study aimed to evaluate the feasibility of quantifying iodine-131 (131I) accumulation in scintigraphy images and compare planar and single-photon emission computed tomography (SPECT) images to estimate 131I radioactivity in patients receiving radioactive iodine therapy for thyroid cancer. We evaluated 72 sets of planar and SPECT images acquired between February 2017 and December 2018. Simultaneously, we placed a reference 131I capsule next to the patient during image acquisition. We evaluated the correlation between the intensity of the capsule in the images and the capsule dose and estimated the radiation dose at the thyroid bed. The mean capsule dose was 2.14 MBq (range, 0.63–4.31 MBq). The correlation coefficients (p-value) between capsule dose and maximum and mean intensities in both planar and SPECT images were 0.93 (p < 0.01), 0.96 (p < 0.01), 0.60 (p < 0.01), and 0.47 (p < 0.01), respectively. The mean intensities of planar images show the highest correlation coefficients. Based on a regression equation, the average radiation dose in the thyroid bed was 5.9 MBq. In conclusion, planar images reflected the radiation dose more accurately than SPECT images. The regression equation allows to determine the dose in other regions, such as the thyroid bed or sites of distant metastasis.

Dual-layer collimator for improved spatial resolution in SPECT with CZT cameras: An analytical and Monte Carlo study

Current hole matching pixel detector (HMPD) collimators for SPECT imaging exist in two configurations: one hole per pixel (1HMPD) or four holes per pixel (4HMPD). The aim of this study was to assess the performance of a dual-layer collimator made by stacking up these two collimator types (1H/4HMDP) for low and medium-energy gamma emitters. Analytical equations describing 1H/4HMDP collimator geometrical efficiency and full width at half maximum (FWHM) were derived. In addition, a fast dedicated gamma ray-tracing Monte Carlo (MC) code was developed to assess the collimator’s point spread function (PSF) and to simulate planar and SPECT acquisitions. A relative agreement between analytical equations and MC simulations better than 3% was observed for the efficiency and better than 1% for the FWHM. The length of the two layers was optimized to get the best spatial resolution while keeping the geometrical efficiency equal to that of the 45mm-length 1HMPD collimator. An optimized combination of the 1H/4HMPD configuration with respective hole lengths of 20mm and 12.95mm has been derived. For source-collimator distances above 5 cm and equal collimator geometrical efficiency, the spatial resolution of this optimal 1H/4HMDP collimator supersedes that of the 45mm-length 1HMPD collimator, and that of the 19.1mm-length 4HMPD collimator. This improvement was observed in simulations of bar phantoms planar images and of hot rods phantom SPECT. Remarkably, the spatial resolution was preserved along the depth of the Jaszczak phantom slices. The 1H/4HMDP collimator is a promising solution for CZT SPECT imaging of low- and medium-energy emitters.

Dual-layer collimator for improved spatial resolution in SPECT with CZT cameras: An analytical and Monte Carlo study

Current hole matching pixel detector (HMPD) collimators for SPECT imaging exist in two configurations: one hole per pixel (1HMPD) or four holes per pixel (4HMPD). The aim of this study was to assess the performance of a dual-layer collimator made by stacking up these two collimator types (1H/4HMDP) for low and medium-energy gamma emitters. Analytical equations describing 1H/4HMDP collimator geometrical efficiency and full width at half maximum (FWHM) were derived. In addition, a fast dedicated gamma ray-tracing Monte Carlo (MC) code was developed to assess the collimator’s point spread function (PSF) and to simulate planar and SPECT acquisitions. A relative agreement between analytical equations and MC simulations better than 3% was observed for the efficiency and better than 1% for the FWHM. The length of the two layers was optimized to get the best spatial resolution while keeping the geometrical efficiency equal to that of the 45mm-length 1HMPD collimator. An optimized combination of the 1H/4HMPD configuration with respective hole lengths of 20mm and 12.95mm has been derived. For source-collimator distances above 5 cm and equal collimator geometrical efficiency, the spatial resolution of this optimal 1H/4HMDP collimator supersedes that of the 45mm-length 1HMPD collimator, and that of the 19.1mm-length 4HMPD collimator. This improvement was observed in simulations of bar phantoms planar images and of hot rods phantom SPECT. Remarkably, the spatial resolution was preserved along the depth of the Jaszczak phantom slices. The 1H/4HMDP collimator is a promising solution for CZT SPECT imaging of low- and medium-energy emitters.

An optimized imaging protocol for [99mTc]Tc-DPD scintigraphy and SPECT/CT quantification in cardiac transthyretin (ATTR) amyloidosis

Background In [99mTc]Tc-DPD scintigraphy for myocardial ATTR amyloidosis, planar images 3 hour p.i. and SPECT/CT acquisition in L-mode are recommended. This study investigated if earlier planar images (1 hour p.i.) are beneficial and if SPECT/CT acquisition should be preferred in H-mode (180° detector angle) or L-mode (90°). Methods In SPECT/CT phantom measurements (NaI cameras, N = 2; CZT, N = 1), peak contrast recovery (CRpeak) was derived from sphere inserts or myocardial insert (cardiac phantom; signal-to-background ratio [SBR], 10:1 or 5:1). In 25 positive and 38 negative patients (reference: endomyocardial biopsy or clinical diagnosis), Perugini scores and heart-to-contralateral (H/CL) count ratios were derived from planar images 1 hour and 3 hour p.i. Results In phantom measurements, accuracy of myocardial CRpeak at SBR 10:1 (H-mode, 0.95-0.99) and reproducibility at 5:1 (H-mode, 1.02-1.14) was comparable for H-mode and L-mode. However, L-mode showed higher variability of background counts and sphere CRpeak throughout the field of view than H-mode. In patients, sensitivity/specificity were ≥ 95% for H/CL ratios at both time points and visual scoring 3 hour. At 1 hour, visual scores showed specificity of 89% and reduced reader’s confidence. Conclusions Early DPD images provided no additional value for visual scoring or H/CL ratios. In SPECT/CT, H-mode is preferred over L-mode, especially if quantification is applied apart from the myocardium.