A Omidi¹*, E Weiss², J Wilson^1,3, M Rosu-Bubulac², (1) Department of Biomedical Engineering, School of Engineering, Virginia Commonwealth University, Richmond, VA, (2) Department of Radiation Oncology, School of Medicine, Virginia Commonwealth University, Richmond, VA, (3) Pauley Heart Center, School of medicine, Virginia Commonwealth University, Richmond, VA,

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  A Omidi

MO-E115-IePD-F6-3 (Monday, 7/11/2022) 1:15 PM - 1:45 PM [Eastern Time (GMT-4)]

Exhibit Hall | Forum 6

Purpose: Radiotherapy for the lung cancer treatment is often planned on the average-intensity image set (AVE) derived from 4DCT, in which organs at risk, namely, the left ventricle (LV) structure is blurred due to breathing/cardiac motion and the lack of contrast inhibits true delineation of LV myocardium (LVM) and exclusion of blood pool. In a first study of its kind, we assessed the relative effects of cardiac/respiratory motion in estimating radiotherapy dose to the LV and LVM.

Methods: 8 lung cancer patients undergoing radiotherapy were recruited for this study. Each patient underwent a 4DCT (10 breathing phases), an exhale breath-hold T1-VIBE, and an exhale breath-hold cine MR (25 cardiac phases). LV/LVW were contoured on 4DCT/cine, respectively. The dose from the planning AVE image set was propagated via the following workflows: (A) every respiratory phase: AVE_CT→0%-90% 4DCT respiratory phases. (B) every cardiac phase (at exhale): AVE_CT→Exh_CT (50% phase)→Exh_T1-VIBE→Exh_average_cine_MRI→cine_MRI cardiac phases. (C) cine arbitrary reference-phase (cumulative LVM dose over cardiac cycle): Cine_MRI cardiac phases→Cine_MRI arbitrary reference-phase (via deformable image registration). All dose values were normalized by the mean dose from AVE_CT.

Results: The normalized max/mean dose (±standard deviations) for the LV respiratory phases and LVM cardiac phases ranged between 4.9(±2.2)-5.8(±2.3)/0.9(±0.1)-1.2(±0.1) and 5.5(±2.2)-8.3(±4)/ 1.1(±0.1)-1.4(±0.3), respectively. At exhale, the normalized max/mean dose from the accumulated dose on cine MR at LVM (cardiac motion only) was insignificantly higher than the dose on non-cardiac-gated 50%-CT at the LV: 5.9(±2.6)/1.3(±0.2) vs 5.2(±2.3)/1.1(±0.1), p>0.17.

Conclusion: The obtained results suggest that the dose distribution on the LV/LVM can differ during various respiratory/cardiac phases. Due to a better LVM delineation (exclusion of blood pool) and dose-accumulation based on cardiac-motion only, Cine MRI application seems to be beneficial in dose-assessments compared to non-cardiac-gated CT only. This finding requires careful consideration when evaluating the risk of cardiotoxicity secondary to radiotherapy.

Keywords

MRI, Dose, CT

Taxonomy

IM/TH- MRI in Radiation Therapy: MRI for treatment planning

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