Modelling SPECT auto-contouring acquisitions for 177 Lu & 131 I molecular radiotherapy using new developments in Geant4/GATE

• Published in: Physica medica 2022-04, Vol.96, p.101
• Main Authors: Kayal, Gunjan, Chauvin, Maxime, Mora-Ramirez, Erick, Clayton, Naomi, Vergara-Gil, Alex, Tran-Gia, Johannes, Lassmann, Michael, Calvert, Nicholas, Tipping, Jill, Struelens, Lara, Bardiès, Manuel
• Format: Article
• Language: English
• Subjects: Gamma Cameras; Humans; Iodine Radioisotopes - therapeutic use; Monte Carlo Method; Phantoms, Imaging; Tomography, Emission-Computed, Single-Photon - methods
• ISSN: 1724-191X
• DOI: 10.1016/j.ejmp.2022.03.003

Monte Carlo modelling of SPECT imaging in Molecular Radiotherapy can improve activity quantification. Until now, SPECT modelling with GATE only considered circular orbit (CO) acquisitions. This cannot reproduce auto-contour acquisitions, where the detector head moves close to the patient to improve image resolution. The aim of this work is to develop and validate an auto-contouring step-and-shoot acquisition mode for GATE SPECT modelling. Lu and I SPECT experimental acquisitions performed on a Siemens Symbia T2 and GE Discovery 670 gamma camera, respectively, were modelled. SPECT projections were obtained for a cylindrical Jaszczak phantom and a lung and spine phantom. Detector head parameters (radial positions and acquisition angles) were extracted from the experimental projections to model the non-circular orbit (NCO) detector motion. The gamma camera model was validated against the experimental projections obtained with the cylindrical Jaszczak ( Lu) and lung and spine phantom ( I). Then, Lu and I CO and NCO SPECT projections were simulated to validate the impact of explicit NCO modelling on simulated projections. Experimental and simulated SPECT images were compared using the gamma index, and were in good agreement with gamma index passing rate (GIPR) and gamma of 96.27%, 0.242 ( Lu) and 92.89%, 0.36 ( I). Then, simulated Lu and I CO and NCO SPECT projections were compared. The GIPR, gamma between the two gamma camera motions was 99.85%, 0.108 for Lu and 75.58%, 0.6 for I. This work thereby justifies the need for auto-contouring modelling for isotopes with high septal penetration.