Accurate, repeatable, and geometrically precise diffusion-weighted imaging on a 0.35 T magnetic resonance imaging-guided linear accelerator

Joseph Weygand; Tess Armstrong; John Michael Bryant; Jacqueline M Andreozzi; Ibrahim M Oraiqat; Steven Nichols; Casey L Liveringhouse; Kujtim Latifi; Kosj Yamoah; James R Costello; Jessica M Frakes; Eduardo G Moros; Issam M El Naqa; Arash O Naghavi; Stephen A Rosenberg; Gage Redler

doi:10.1016/j.phro.2023.100505

Accurate, repeatable, and geometrically precise diffusion-weighted imaging on a 0.35 T magnetic resonance imaging-guided linear accelerator

Phys Imaging Radiat Oncol. 2023 Nov 8:28:100505. doi: 10.1016/j.phro.2023.100505. eCollection 2023 Oct.

Authors

Joseph Weygand¹, Tess Armstrong², John Michael Bryant¹, Jacqueline M Andreozzi¹, Ibrahim M Oraiqat¹, Steven Nichols¹, Casey L Liveringhouse¹, Kujtim Latifi¹, Kosj Yamoah¹, James R Costello³, Jessica M Frakes¹, Eduardo G Moros¹, Issam M El Naqa^{1

4}, Arash O Naghavi¹, Stephen A Rosenberg¹, Gage Redler¹

Affiliations

¹ Department of Radiation Oncology, Moffitt Cancer Center, Tampa, FL, USA.
² ViewRay Inc., Cleveland, OH, USA.
³ Department of Radiology, Moffitt Cancer Center, Tampa, FL, USA.
⁴ Department of Machine Learning, Moffitt Cancer Center, Tampa, FL, USA.

Abstract

Background and purpose: Diffusion weighted imaging (DWI) allows for the interrogation of tissue cellularity, which is a surrogate for cellular proliferation. Previous attempts to incorporate DWI into the workflow of a 0.35 T MR-linac (MRL) have lacked quantitative accuracy. In this study, accuracy, repeatability, and geometric precision of apparent diffusion coefficient (ADC) maps produced using an echo planar imaging (EPI)-based DWI protocol on the MRL system is illustrated, and in vivo potential for longitudinal patient imaging is demonstrated.

Materials and methods: Accuracy and repeatability were assessed by measuring ADC values in a diffusion phantom at three timepoints and comparing to reference ADC values. System-dependent geometric distortion was quantified by measuring the distance between 93 pairs of phantom features on ADC maps acquired on a 0.35 T MRL and a 3.0 T diagnostic scanner and comparing to spatially precise CT images. Additionally, for five sarcoma patients receiving radiotherapy on the MRL, same-day in vivo ADC maps were acquired on both systems, one of which at multiple timepoints.

Results: Phantom ADC quantification was accurate on the 0.35 T MRL with significant discrepancies only seen at high ADC. Average geometric distortions were 0.35 (±0.02) mm and 0.85 (±0.02) mm in the central slice and 0.66 (±0.04) mm and 2.14 (±0.07) mm at 5.4 cm off-center for the MRL and diagnostic system, respectively. In the sarcoma patients, a mean pretreatment ADC of 910x10^-6 (±100x10^-6) mm²/s was measured on the MRL.

Conclusions: The acquisition of accurate, repeatable, and geometrically precise ADC maps is possible at 0.35 T with an EPI approach.

Keywords: Apparent diffusion coefficient; Cellularity; Diffusion weighted imaging; MRI-guided radiotherapy.