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Background: Optimal peptide concentration in treatment with 177Lu-DOTATOC/DOTATATE is amatter of debate. Most of the studies with peptide receptor radionuclide therapy mention peptidedose ranging between 100 and 250 µg. The aim of this is to identify possible differences inradiation-absorbed doses (D/Gy) to tumor and kidney as a function of the peptide mass dose in orderto identify the most suitable peptide dose for treatment. The therapeutic index (Dtumor/Dkidneys) wasassessed as a key parameter for the treatment response. Materials and Methods: Five patients withmetastasized Grade 1 to Grade 2 neuroendocrine tumor were analyzed in this study. Patients (n = 4)received two cycles of treatment with intravenously injected 177Lu-DOTATOC containing peptidemass doses of 200 µg and 90 µg, alternatively; one patient was treated with 90 µg peptide massin both the therapy cycles. Whole-body (head to mid-thigh) three-dimensional single-photonemission computerized tomography (3D SPECT)/CT images were acquired at 1, 4, 24, 48, and72 h following the injection of 177Lu-DOTATOC. Attenuation correction for 3D SPECT images wasperformed using CT data acquired and fused with the SPECT data (SPECT/CT). Results: Overall, 28 target lesions (liver n = 17, lung n = 4, lymph nodes n = 1, and bone n = 2) were analyzed after 1st and 2nd therapy cycles. Tumor normalized absorbed doses varied by a factor of 74 between 0.35 and26 mGy/MBq. Averaged over all patients, a higher normalized mean tumor dose (10.51 mGy/MBq)was achieved for a peptide dose of 200 µg compared to 90 µg (4.58 mGy/MBq). Kidneys dosesvaried by a factor of up to 4 between patients (0.25-1.0 mGy/MBq) (independent of dose cycle andpeptide dose) and by a factor of up to 2 between dose cycles. The mean kidney dose was 13.7%higher for the 90 µg peptide dose compared to 200 µg. Given the higher tumor dose, the meantherapeutic index of a 200 µg mass dose was considerably higher (16.95), compared to a 90 µg massdose (9.63). This coincided with the observation, that lesion volume reduction was more pronouncedafter an initial treatment with a 200 µg mass dose. Biologically effective dose was only 5. 1%-19.3%higher than the absorbed dose for individual dose cycles. Conclusions: Higher peptide dose of 200µg appears to be more suitable than 90 µg in terms of tumor dose, kidney dose, and therapeuticindex for treatment with 177Lu-DOTATOC. [ABSTRACT FROM AUTHOR]

Purpose: Quantitative estimates of dopamine transporter availability, determined with [I]FP-CIT SPECT, depend on the SPECT equipment, including both hardware and (reconstruction) software, which limits their use in multicentre research and clinical routine. This study tested a dedicated reconstruction algorithm for its ability to reduce camera-specific intersubject variability in [I]FP-CIT SPECT. The secondary aim was to evaluate binding in whole brain (excluding striatum) as a reference for quantitative analysis. Methods: Of 73 healthy subjects from the European Normal Control Database of [I]FP-CIT recruited at six centres, 70 aged between 20 and 82 years were included. SPECT images were reconstructed using the QSPECT software package which provides fully automated detection of the outer contour of the head, camera-specific correction for scatter and septal penetration by transmission-dependent convolution subtraction, iterative OSEM reconstruction including attenuation correction, and camera-specific 'to kBq/ml' calibration. LINK and HERMES reconstruction were used for head-to-head comparison. The specific striatal [I]FP-CIT binding ratio (SBR) was computed using the Southampton method with binding in the whole brain, occipital cortex or cerebellum as the reference. The correlation between SBR and age was used as the primary quality measure. Results: The fraction of SBR variability explained by age was highest (1) with QSPECT, independently of the reference region, and (2) with whole brain as the reference, independently of the reconstruction algorithm. Conclusion: QSPECT reconstruction appears to be useful for reduction of camera-specific intersubject variability of [I]FP-CIT SPECT in multisite and single-site multicamera settings. Whole brain excluding striatal binding as the reference provides more stable quantitative estimates than occipital or cerebellar binding. [ABSTRACT FROM AUTHOR]

Purpose In peptide receptor radionuclide therapy (PRRT) the kidneys are considered an organ at risk for radiation-induced damage. Thus the absorbed dose to the kidneys is one important safety parameter with the potential to influence treatment regimen and therefore treatment outcome. Dosimetry can be performed using planar, hybrid (planar/SPECT) or SPECT imaging. The choice of modality is expected to impact the results. In this work we aimed to compare (1) the different modalities and (2) different planar correction/calibration methods. Methods Retrospective planar, hybrid and 3D dosimetry analysis was performed using the internal dosimetry software suite QDOSE. Five patients with neuroendocrine tumours, who received 177 Lu-Dotatate PRRT and were imaged at time points at 0.5 h, 4 h, 24 h and 96 h post-injection, were analyzed. SPECT data were reconstructed with 3D OSEM including attenuation and scatter correction. Planar corrections included attenuation correction using a broad beam μ and background correction. The activity calibration of the planar data was performed either using the activity in the whole body (WB) or a reference vial. Phantom-based dose calculations were performed using IDAC-Dose 2.1. Results Comparing modalities, using 3D SPECT as reference, the absorbed dose to the kidneys was overestimated by 95% when calculated with planar methodology and by 13% when hybrid dosimetry was applied. Regarding planar corrections, there was only a moderate difference between vial and WB calibration of −14% when all corrections were applied. However, vial calibration without attenuation correction resulted in a large deviation of −58% compared to full correction. When WB calibration was applied, no correction performed slightly better (−8% deviation) than only attenuation correction (+9%) or only background correction (−14%) compared to full correction. Conclusions For quantitative accuracy 3D SPECT dosimetry is preferable. If planar imaging is used, overlapping activity can cause significant overestimation of activity and hence absorbed dose for the kidneys. As absorbed dose limits (23Gy–29Gy) are commonly applied to the kidneys, dosimetry results based on planar imaging could potentially impede treatment efficacy by artificially restricting the administered therapeutic activity. Hybrid dosimetry provided a sufficiently accurate compromise between the higher acquisition time demands of 3D dosimetry and limited accuracy of planar dosimetry. [ABSTRACT FROM AUTHOR]

The design of an optimal feedforward controller in active noise control applications for controlling the sound radiation from a vibrating structure can be seen as a system identification problem. Most control implementations use a stochastic gradient search algorithm to adaptively identify the impulse response of the optimal control filter. The convergence properties of the widely used filtered-x LMS algorithm depend on the signal properties of the filtered reference signals. Sensing the reference signals from the vibrating structure is inevitable in most real applications and will effectively result in structural filtering of the unknown noise source. The filtered reference signals from a structural sensor generally exhibit a large eigenvalue spread resulting in poor convergence properties of the adaptive controller. A new extended-filtered-x approach has been developed which makes the implementation of fast RLS type algorithms possible. These algorithms are based on an orthogonal projection of the predictor error into the subspace of the filtered reference signals and therefore converge independent from the underlying signal statistics. Experiments for active control of noise from a vibrating plate have been conducted which demonstrate the superior control performance of fast transversal filters. [ABSTRACT FROM AUTHOR]