2236 - Acute Cardiac Inflammation 1-Year after Left-Sided Breast Cancer Radiotherapy Assessed with Hybrid PET/MRI

O. W. Chau^1,2, A. Islam³, M. I. Lock⁴, E. Yu⁵, R. Dinniwell⁶, B. P. Yaremko⁷, M. Brackstone⁷, W. Pavlosky³, J. Butler³, H. Biernaski³, M. Kovacs¹, C. Graf³, G. Wisenberg³, F. Prato³, and S. Gaede⁷; ¹Western University, London, ON, Canada, ²University of California, San Francisco, San Francisco, CA, ³Lawson Health Research Institute, London, ON, Canada, ⁴Department of Radiation Oncology, London Health Sciences Centre, London, ON, Canada, ⁵Department of Radiation Oncology, Western University, London, ON, Canada, ⁶niagara health, niagara, ON, Canada, ⁷London Health Sciences Centre, London, ON, Canada

Purpose/Objective(s): In this pilot study, we test the utility of hybrid PET/MRI and circulating biomarkers to non-invasively detect early cardiac inflammatory and functional responses at one month and one year follow-up, simultaneously after radiation therapy (RT) in patients with left-sided breast cancer. Materials/

Methods: Fifteen left-sided breast cancer patients enrolled in the RICT-BREAST study underwent hybrid PET/MRI cardiac imaging at baseline, 1-month, and 1-year after standard RT. Thirteen patients had scans at baseline, eleven patients had 1-month follow-up scans, while ten patients had scans at 1-year. Overall, eight patients had scans at all timepoints, and ten patients had both 1-month and 1-year follow-up scans. For each scan, a 60-minute list-mode ¹⁸FDG/PET scan with prior glucose suppression was acquired. Regional myocardial inflammation was quantified by calculating the percent change of mean ¹⁸FDG standard uptake (meanSUV_bw) at 40-60 minutes post-injection, based on the supplying artery (left anterior descending (LAD), left circumflex or right coronary artery).

LV functional matrices were quantified from MR cine images and late gadolinium images acquired simultaneously during PET imaging. Circulating biomarker measurements of high-sensitivity troponin T, C-reactive protein and erythrocyte sedimentation rate were also compared at each timepoint.
Results: A significant increase of ¹⁸FDG/PET myocardial uptake (meanSUV_bw) in LAD segments (p = 0.04, 0.14, 10%.) was detected at 1-month follow-up in 8 of 11 patients up. However, in only 5 of 10 patients increased uptake was observed in LAD segments at 1-year follow-up compared to 1-month (mean of 0.1) and 4 of 8 had an increase at 1-year compared to baseline (mean increase of 0.2). However, it was insignificant (p = 0.96). A significant reduction of LV stroke volume (p < 0.03, < -7%) was identified both at 1-month and 1-year follow-up. No significant changes in any biomarkers were seen at both follow-up timepoints. No abnormal enhancement from late gadolinium MR images was observed across patients at 1-year timepoint.
Conclusion: 18FDG/PET-MRI can simultaneously detect cardiac inflammation, functional response changes, and LV stroke volume changes in left-sided breast cancer patients as early as 1-month post radiotherapy, which, in some patients, persists out to one year. Clinical outcomes must be tracked to determine the predictive value of these biomarkers