Dosimetric impact of geometric distortions in an MRI-only proton therapy workflow for lung, liver and pancreas

Dumlu, Hatice Selcen; Meschini, Giorgia; Kurz, Christopher; Kamp, Florian; Baroni, Guido; Belka, Claus; Paganelli, Chiara und Riboldi, Marco (2022): Dosimetric impact of geometric distortions in an MRI-only proton therapy workflow for lung, liver and pancreas. In: Zeitschrift für Medizinische Physik, Bd. 32, Nr. 1: S. 85-97

Abstract

In a radiation therapy workflow based on Magnetic Resonance Imaging (MRI), dosimetric errors may arise due to geometric distortions introduced by MRI. The aim of this study was to quantify the dosimetric effect of system-dependent geometric distortions in an MRI-only workflow for proton therapy applied at extra-cranial sites. An approach was developed, in which computed tomography (CT) images were distorted using an MRI displacement map, which represented the MR distortions in a spoiled gradient-echo sequence due to gradient nonlinearities and static magnetic field inhomogeneities. A retrospective study was conducted on 4DCT/MRI digital phantoms and 18 4DCT clinical datasets of the thoracoabdominal site. The treatment plans were designed and separately optimized for each beam in a beam specific Planning Target Volume on the distorted CT, and the final dose distribution was obtained as the average. The dose was then recalculated in undistorted CT using the same beam geometry and beam weights. The analysis was performed in terms of Dose Volume Histogram (DVH) parameters. No clinically relevant dosimetric impact was observed on organs at risk, whereas in the target structure, geometric distortions caused statistically significant variations in the planned dose DVH parameters and dose homogeneity index (DHI). The dosimetric variations in the target structure were smaller in abdominal cases (Delta D-2%, Delta D-98%, and Delta D-mean all below 0.1% and Delta DHI below 0.003) compared to the lung cases. Indeed, lung patients with tumors isolated inside lung parenchyma exhibited higher dosimetric variations (Delta D-2% >= 0.3%, Delta D-98% >= 15.9%, Delta D-mean >= 3.3% and Delta DHI >= 0.102) than lung patients with tumor close to soft tissue (Delta D2% < 0.4%, Delta D-98% <= 5.6%, Delta D-mean <= 0.9% and Delta DHI <= 0.027) potentially due to higher density variations along the beam path. Results suggest the potential applicability of MRI-only proton therapy, provided that specific analysis is applied for isolated lung tumors.

• Dokumententyp: Zeitschriftenartikel
• Fakultät: Physik
• Themengebiete: 500 Naturwissenschaften und Mathematik > 530 Physik
• ISSN: 0939-3889
• Sprache: Englisch