Annemarijke Van Luijtelaar¹, J.P. Michiel Sedelaar², Joyce G.R. Bomers¹, and Jurgen J. Fütterer^1
1Medical Imaging, Radboudumc Nijmegen, Nijmegen, Netherlands, ²Urology, Radboudumc Nijmegen, Nijmegen, Netherlands

Magnetic resonance imaging-guided focal laser ablation is used as alternative to radical treatment while preserving healthy tissue and subsequently reduce treatment-related morbidity in patients with localized prostate cancer. Preliminary results of this prospective, non-randomized, clinical phase 2 study using a remote-controlled manipulator, show promising results in both oncological and functional outcomes in a group of 20 patients with low- to intermediate-risk (Gleason Score ≤ 4+3) prostate cancer. Transrectal magnetic resonance imaging-guided focal laser ablation is a promising outpatient procedure under local anesthesia for localized prostate cancer. It provides a fast and minimally-invasive strategy while reducing treatment related complications and side-effects.

Derk J. Slotman^1,2, Lambertus W. Bartels², Aylene Zijlstra¹, Inez M. Verpalen¹, Jochen A.C. van Osch¹, Ingrid M. Nijholt¹, Edwin Heijman^3,4, Miranda van 't Veer-ten Kate¹, Erwin de Boer¹, Rolf D. van den Hoed¹, Martijn Froeling², and Martijn F. Boomsma^1
1Radiology, Isala Zwolle, Zwolle, Netherlands, ²Image Sciences Institute, Imaging & Oncology Division, University Medical Center Utrecht, Utrecht, Netherlands, ³Faculty of Medicine and University Hospital of Cologne, Institute of Diagnostic and Interventional Radiology, University of Cologne, Cologne, Germany, ⁴High Tech Campus, Philips Research Eindhoven, Eindhoven, Netherlands

The non-perfused volume (NPV) cannot be assessed repeatedly with contrast-enhanced imaging during MR-HIFU ablations of uterine fibroids, due to contrast agent dose constraints and safety concerns. In this study, synthetic contrast-enhanced (CE)-T1w scans were generated from diffusion weighted imaging (DWI) using deep learning-based image-to-image translation. A significant linear association was found between the NPV-ratios based on synthetic and paired reference CE-T1w scans (r=0.80, p<0.001). Radiologists agreed in 83% on treatment success based on synthetic and reference CE-T1w scans. This indicates that translation of DWI into synthetic CE-T1w scans has potential as method for gadolinium-free imaging of the NPV.

Danny Lee¹, Seungjong Oh¹, Min-sig Hwang¹, Mary McCauley¹, Daniel Pavord¹, Kyung Lim Yun¹, Jason Sohn^1,2, and Alexander V. Kirichenko^1,2
1Radiation Oncology, Allegheny Health Network, Pittsburgh, PA, United States, ²Drexel University, Philadelphia, PA, United States

Ablative SBRT to liver malignancies on MRI-Linac is a novel and rapidly evolving technology allowing visualization of tumor and nearby organs at risk (OAR). Reliable identification of liver tumors has direct impact on radiotherapy planning and outcome. SPION agent Ferumoxytol® (Feraheme, AMAG Pharmaceuticals, Waltham, MA) was applied as MRI contrast during adaptive planning on Elekta Unity MR-Linac. Compared to the non-contrast images, liver tumors after Ferumoxytol® injection, were superiorly visible for accurate delineation during the entire treatment course. This study is the first to report the impact of SPION contrast agent on liver tumor visualization in a 1.5T Elekta MR-Linac.

Katrinus Keijnemans¹, Pim Borman¹, Bas Raaymakers¹, and Martin Fast^1
1Department of Radiotherapy, University Medical Center Utrecht, Utrecht, Netherlands

In MR-guided abdominothoracic radiotherapy, fast 2D imaging for MLC tracking and respiratory-correlated 4D imaging for dose accumulation is desirable. We developed a hybrid 2D/4D MRI method for pre-beam and beam-on imaging, which continuously acquires and reconstructs T2_w coronal simultaneous multi-slice (SMS) images. Pre-beam 4D-MRIs were used to calculate a 3D mid-position reference image. Beam-on SMS data were used to extract real-time motion using a 4D-based motion model, and continuous 4D-MRIs. Dynamic updating of the 4D-motion model yielded the best real-time motion estimation. The presented hybrid 2D/4D MRI method can potentially facilitate novel MR-guided abdominothoracic radiotherapy workflows.

Junzhou Chen^1,2, Pei Han^2,3, Ye Tian⁴, Wensha Yang⁵, Debiao Li^6,7, Krishna Nayak⁴, Yingli Yang⁸, Anthony Christodoulou^6,9, and Zhaoyang Fan^1,5,10
1Radiology, University of Southern California, Los Angeles, CA, United States, ²Bioengineering, University of California, Los Angeles, Los Angeles, CA, United States, ³Biomedical Imaging Research Institute, Cedars-Sinai Medical Center, Los Angeles, CA, United States, ⁴Electrical Engineering, University of Southern California, Los Angeles, CA, United States, ⁵Radiation Oncology, University of Southern California, Los Angeles, CA, United States, ⁶Cedars-Sinai Medical Center, Los Angeles, CA, United States, ⁷University of California, Los Angeles, Los Angeles, CA, United States, ⁸Radiation Oncology, University of California, Los Angeles, Los Angeles, CA, United States, ⁹Bioengineering, Cedars-Sinai Medical Center, Los Angeles, CA, United States, ¹⁰Biomedical Engineering, University of Southern California, Los Angeles, CA, United States

MR applications in radiation therapy has shown great promise for highly conformal treatment. However, MRgRT in the abdomen remains challenging due to motion and the sheer number of organs. In this work, we have demonstrated an integrated multi-task MR platform for adaptive radiation planning and treatment monitoring in the abdomen. In our proposed framework, from a single "pre-beam" scan we are able to generate a volumetric, multi-contrast and motion resolved images for adaptive treatment planning as well as enabling multi-contrast 3D real-time display during treatment. We demonstrate this capability in 3T and 0.55T.

Can Wu¹, Neelam Tyagi¹, Marsha Reyngold², Christopher Crane², and Ricardo Otazo^1,3
1Department of Medical Physics, Memorial Sloan Kettering Cancer Center, New York, NY, United States, ²Department of Radiation Oncology, Memorial Sloan Kettering Cancer Center, New York, NY, United States, ³Department of Radiology, Memorial Sloan Kettering Cancer Center, New York, NY, United States

Real-time 3D MRI for low-latency volumetric motion tracking was successfully implemented on a 1.5T MR-Linac system using the MRSIGMA framework. A first scan was performed for offline learning to obtain a training dictionary of ten 3D motion states. A second scan with the same sequence parameters was performed to generate the motion signature in real-time for online matching and was also used as a reference for retrospective self-validation. The feasibility of the technique was demonstrated on a healthy volunteer and a patient with pancreatic cancer which presented high quantitative concordance between contours of real-time MRSIGMA matching and the reference.

Qihao Zhang¹, Kyungmouk Steve Lee², Thanh Nguyen³, Pascal Spincemaille², and Yi Wang^2
1Cornell University, Ithaca, NY, NY, United States, ²Weill Cornell Medical College, New York, NY, United States, ³Cornell University, New York, NY, United States

Trans-arterial radioembolization with yttrium-90 microspheres (TARE with Y90) is a treatment for patients with liver cancers, but requires the evaluation of lung shunting fraction (LSF). Currently, LSF is estimated using a separate invasive “dry-run” with a transient radioactive Technetium-99m macroaggregated albumin (Tc-99m-MAA) that doubles the cost and risk of TARE. This study proposes to predict LSF from dynamic contrast enhanced MRI (DCE MRI) and perfusion quantification. Our preliminary data demonstrated that it is feasible to estimate LSF as measured by Tc-99m-MAA from  noninvasive DCE MRI using quantitative transport mapping (QTM) velocity.