Andreas Wetscherek¹, Brigid A McDonald², Ernst S Kooreman³, Angus Z Lau^4,5, Ramesh Paudyal⁶, Amita Shukla-Dave^6,7, Liam SP Lawrence^4,5, Petra J van Houdt³, and Uulke A van der Heide^3
1Joint Department of Physics, The Institute of Cancer Research and The Royal Marsden NHS Foundation Trust, London, United Kingdom, ²Department of Radiation Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX, United States, ³Department of Radiation Oncology, The Netherlands Cancer Institute, Amsterdam, Netherlands, ⁴Physical Sciences Platform, Sunnybrook Research Institute, Toronto, ON, Canada, ⁵Department of Medical Biophysics, University of Toronto, Toronto, ON, Canada, ⁶Department of Medical Physics, Memorial Sloan Kettering Cancer Center, New York, NY, United States, ⁷Department of Radiology, Memorial Sloan Kettering Cancer Center, New York, NY, United States

Measuring the detectable effect size is crucial for setting up clinical trials involving quantitative MRI for treatment adaptation, response assessment and outcome prediction in MR-guided radiotherapy. For four different tumor sites (brain, head and neck, prostate and rectum) diffusion-weighted MRI protocols were optimized for intravoxel incoherent motion imaging based on minimizing the mean relative error of the IVIM parameters. For full IVIM model fits,  4-5 b-values were found optimal, while a fit with fixed D* was best performed with 3 b-values. MR-Linac systems currently have limitations regarding gradient performance and number of coil channels and qMRI techniques require careful optimization.

Louis Marage¹, Igor Bessières¹, Magali Quivrin², Aubignac Léone¹, Karine Peignaux-Casanovas², Gilles Truc², Paul-Michael Walker¹, and Stanislas Rapacchi^3
1Medical Physics, Centre Georges-François Leclerc, Dijon, France, ²Radiotherapy, Centre Georges-François Leclerc, Dijon, France, ³Aix-Marseille Univ, CNRS, CRMBM, Marseille, France

-       The proposed method allows a comprehensive relaxation times estimation (T1, T2, T2*) on MRgRT systems.

-       The methodology was validated on phantom and volunteer for accuracy and reproducibility.

-       For T1 and T2, less than 5 % coefficient of variation was observed and less than 10 % for the T2*.

-       Trends on 5 patients show a slight decrease and a recovery for the T1 and T2 values in both the boost and whole prostate during their treatment.
 

-       The dispersion of T1 and T2 decreased for all patients for the whole prostate whereas it was stable for the boost.

Wajiha Bano¹, Kobika Sritharan², Uwe Oelfke¹, Alison Tree², and Andreas Wetscherek^1
1Joint Department of Physics, The Institute of Cancer Research and The Royal Marsden NHS Foundation Trust, London, United Kingdom, ²Department of Radiotherapy, The Royal Marsden NHS Foundation Trust, London, United Kingdom

T₂^* mapping can be a potential biomarker to characterise hypoxia and monitor treatment response throughout the course of MR-guided radiotherapy on an MR-Linac. This study explores the feasibility of integrating T₂^* mapping in daily prostate MR-Linac workflow using a cohort of patients with prostate cancer. We compared mean T₂^* values within the prostate with repeated measures acquired twice weekly during radiotherapy. T₂^* values at the end of treatment were higher than at the first fraction but didn’t show a consistent trend throughout treatment. Integrating T₂^* mapping with other functional measurements can aid in response based treatment adaptation. 

Wendy Harris¹, Ergys Subashi¹, Victoria Yu¹, Eric Aliotta¹, Ricardo Otazo¹, and Laura Cervino^1
1Medical Physics, Memorial Sloan Kettering Cancer Center, New York, NY, United States

Current target localization for prostate radiotherapy on a conventional LINAC consists of acquiring a cone-bean CT (CBCT) image and matching it to implanted fiducial markers inside the prostate due to poor soft-tissue contrast of CBCT. MRI provides better soft tissue contrast and no ionization radiation, but there are very few MR-LINACs, and conventional LINACs with x-ray imaging capabilities are much more ubiquitous.  This study proposes to use prior MRI acquisitions, PCA motion modeling, and on-board CBCT from a conventional LINAC to obtain on-board pseudo-MRI for target localization in prostate radiotherapy.

Emilia Palmér¹, Maria Ljungberg^1,2, Anna Karlsson^1,2, Fredrik Nordström^1,2, Karin Petruson³, and Maja Sohlin^1,2
1Department of Radiation Physics, Institute of Clinical Sciences, University of Gothenburg, Gothenburg, Sweden, ²Department of Medical Physics and Biomedical Engineering, Sahlgrenska University Hospital, Gothenburg, Sweden, ³Department of Oncology and Radiotherapy, Institute of Clinical Sciences, University of Gothenburg, Gothenburg, Sweden

In an MRI-only workflow, high geometric fidelity of the MRI data is required. Head and neck (H&N) cancer patients, however, frequently have implants, e.g., dental restorations, causing distortions of the MRI data. Geometric offset maps were computed using B0-map calculated from the Dixon-sequence included in the standard clinical protocol. Even though the implants included in this pre-study did not contribute with a significant geometric offset in the delineated target volume, visualization of the geometric offset maps as such bring additional important information when delineating structures in an MRI-only H&N workflow and could thereby become a promising tool in clinical practice.

Bilal A Tahir^1,2,3, Paul JC Hughes², Jack Atkinson^2,3, Isaac Jadav¹, Joshua R Astley^1,2, Stephen D Robinson^1,4, Alberto Biancardi², Helen Marshall², Kerry A Hart^1,5, James A Swinscoe¹, Rob H Ireland^1,2, Matthew Q Hatton^1,4, and Jim M Wild^2,3
1Department of Oncology and Metabolism, The University of Sheffield, Sheffield, United Kingdom, ²POLARIS, Department of Infection, Immunity and Cardiovascular Disease, The University of Sheffield, Sheffield, United Kingdom, ³Insigneo Institute for in silico medicine, The University of Sheffield, Sheffield, United Kingdom, ⁴Clinical Oncology, Weston Park Cancer Centre, Sheffield, United Kingdom, ⁵Radiotherapy Physics, Weston Park Cancer Centre, Sheffield, United Kingdom

Radiotherapy plays a central role in the management of lung cancer. However, despite advances, survival of lung cancer patients undergoing radiotherapy remains poor, partly attributable to the incidence of radiation-induced lung injury, which is exacerbated in patients with poor pulmonary function. Both ventilation and perfusion information are vital to providing a complete picture of pulmonary function, ideally in a regional fashion. Here, we develop and apply an image acquisition and analysis pipeline to assess dose-related changes in regional lung function as derived from hyperpolarized gas ventilation and dynamic contrast-enhanced perfusion MRI in lung cancer patients receiving a course of radiotherapy.

Matthew John Goette^1,2, Roelf Slopsema³, Anees Dhabaan³, and Hui-Kuo Shu^3
1Radiology and Imaging Sciences, Emory Healthcare, Atlanta, GA, United States, ²Radiation Oncology, Emory Healthcare, Atlanta, GA, United States, ³Radiation Oncology, Emory University, Atlanta, GA, United States

An MR treatment planning simulation protocol for proton therapy in patients with ocular melanoma was optimized using a 70-mm loop coil.

Svein Are Sirirud Vatnehol^1,2, Einar Vik-Mo³, and Ragnhild Marie Undseth^1
1The Intervention Centre, Oslo University Hospital, Oslo, Norway, ²Department of Optometry, Radiography and Lighting Design, University of South-Eastern Norway, Drammen, Norway, ³Department of Neurosurgery, Oslo University Hospital, Oslo, Norway

Intra operative MRI with Diffusion Tensor Imaging allows identification of white mater tracks during surgery allowing for a more aggressive approach by the surgeon while preserving eloquent structures. However DTI is prone to artefacts from B0 inhomogeneity. In this abstract we present our initial experiences on the effect of a commercially available Echo Planar Imaging Correction in the intraoperative setting. While overall image quality is increased, further studies on a larger number of patients are required before the clinical effect can be assessed.  

Andrew J Fagan¹, Krystal Kirby¹, Emily Koons¹, and Kirk M Welker^1
1Radiology, Mayo Clinic, Rochester, MN, United States

This study aimed to investigate the use of 7 Tesla MRI for frameless pre-surgical planning for tumor resection applications.  Image geometric distortions at the locations of 10 skin-adhered fiducials were minimized in 7 Tesla images, and compared to in vivo results from a current 3 Tesla frameless imaging protocol.  Geometric accuracy of < 1 mm was obtained in 7 Tesla images at the surface of a head-shaped phantom.