arXiv subjects

Michel Hesse

Publications and source records attributed to Michel Hesse.

3 recordsLinked to original sources

arXiv2026

Multicenter Comparison of Radionuclide Calibrators and SPECT/CT Protocols for Quantitative 177Lu Imaging in Clinical Practice

Purpose: Following the clinical success of 177Lu-based therapies, accurate quantification of 177Lu using radionuclide calibrators (RNCs) and SPECT/CT is gaining importance as prerequisite for accurate treatment delivery and dosimetry. However, the lack of standardization can introduce inter-system variability, compromising multi-center clinical trials. This study aimed to assess the accuracy and variability of 177Lu measurements using RNCs and SPECT/CT across different systems and hospitals. Methods: A uniform cylindrical phantom and a NEMA phantom with hot spheres were prepared using traceable activities and imaged at 8 different hospitals using 13 SPECT/CT systems (9 conventional and 4 3D CZT). Acquisitions and reconstructions were performed using both site-specific and standardized protocols. The cylindrical phantom images were used to evaluate the system calibration and establish image calibration factors (ICFs), the NEMA images to evaluate effective resolution by calculating recovery coefficients (RCs). In parallel, two vials were measured to test RNC accuracy. Results: RNC measurements differed up to 11% between centers, while SPECT quantification of the cylindrical phantom differed up to 20%. While ICFs were consistent for systems of the same type, image quality varied strongly when using clinical protocols (36% difference in RCs in the largest sphere). Standardized reconstruction reduced variability in RCs for each system type (maximum 12% difference), regardless of acquisition protocol, but differences between system types persisted when standardizing acquisition and reconstruction (33% difference). Conclusion: Current 177Lu measurement practices yield significant variability in quantification and image quality. Harmonization efforts should prioritize standardized calibration and reconstruction protocols to improve multicenter reproducibility of quantitative 177Lu-SPECT/CT.

physics.med-ph↗

arXiv2020

Near 65ps-fwhm in 20mm-LSO TOF-PET by using a time walk correction based on multi-photon stamps: a Monte Carlo study

Aim: Investigate whether a time walk assessment derived from crystal light sharing and multi-photon time stamps can improved the TOF resolution. Method: Monte Carlo simulations were performed for SiPM (FBK-NUV-HD) coupled to conventional 4x4 mm2 pixelated LSO (0.2%Ca:Ce ) and also coupled to 8x4 mm2 pixelated LSO in which a triangular optical window allows light sharing between the two 4x4 mm2 sub-pixels depending on the DOI. A time walk estimation was modelled as a DOI dependent weighted sum of the time differences within the photons detection sequence. The DOI dependent weights were optimized in order to get the best TOF resolution. Results: A strong linear DOI dependence of the light sharing between the two 4x4 mm2 sub-pixels was observed. The TOF resolutions for a 4x4x20 mm3 LSO were 99.7, 81.2, 66.4 ps-fwhm without any correction, with DOI correction and with DOI dependent time walk correction, respectively. The time walk correction was derived from the 7 time stamps of the (2**k )th photons in the sequence, with k within[0,6]. Conclusion: photon time walk can be estimated from the photon time detection series and can be advantageously combined with the DOI assessment to improve TOF resolution.

physics.ins-det↗

arXiv2020

Yttrium-90 TOF-PET based EUD predicts response post liver radioembolizations using standard manufacturer reconstruction parameters

Purpose: Explaining why 90Y TOF-PET based equivalent uniform dose (EUD) using standard FDG reconstruction parameters has been shown to predict response. Methods: The hot rods insert of a Jaszczak deluxe phantom was partially filled with a 2.65 GBq 90Y - 300ml DTPA water solution resulting in a 100 Gy mean absorbed dose in the 6 sectors. A two bed 20min/position acquisition was performed on a 550ps- and on a 320ps- TOF-PET/CT and reconstructed with standard FDG reconstruction parameters, without and with additional filtering. The whole procedure was repeated on both PET after adding a 300ml of water (50Gy setup). The phantom was acquired again after decay by a factor 10 (5Gy setup), but with 200min per bed position. For comparison the phantom was also acquired with 18F activity corresponding to a clinical FDG whole body acquisition. Results: The 100Gy-setup provided hot rod sectors image almost as good as in 18F phantom. However, despite acquisition time compensation the 5Gy-setup provides much lower quality imaging. TOF-PET based sectors EUDs for the three large rod sectors were in agreement with the actual EUDs computed with a radiosensitivity 0.021Gy-1 well in the range observed in external beam radiotherapy (EBRT), i.e. 0.01-0.04Gy-1. This agreement explains the reunification of the dose-response relationships of the glass and resin spheres in HCC using the TOF-PET based EUD. Additional filtering reduced the EUDs agreement quality. Conclusions: Standard FDG reconstruction parameters are suitable in TOF-PET post 90Y liver radioembolization for accurate tumor EUD computation. The present results clearly rules out the use of low specific activity phantom studies to optimize reconstruction parameters.

physics.med-ph↗