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MRI Guided Radiotherapy of Centrally Located Thoracic Tumors: Effect of Cardiac Motion

Y Yang1*, Y Gao1 , F Han3 , P Lee1 , S Rashid2 , J Lamb1 , M Cao1 , D Low1 , P Hu1 , (1) UCLA School of Medicine, Los Angeles, CA, (2) Stony Brook University, Stony Brook, NY, (3) SIEMENS healthscience, Los Angeles, CA


(Sunday, 7/29/2018) 5:05 PM - 6:00 PM

Room: Karl Dean Ballroom B1

Purpose: To achieve optimal treatment results with modern technologies, motion compensation techniques are critical. Much research has been conducted to address breathing-induced tumor motion in radiotherapy (RT) but very few studies looked at the impact of cardiac motion. Intra-fractional soft tissue based motion gating, offered by MRI guided RT, has the potential to greatly reduce treatment uncertainty caused by respiratory motions. However, for some tumors, such as central lung, esophagus or cardiac sarcomas/metastasis, additional efforts may be necessary to evaluate cardiac motion.

Methods: Multi-slice Cardiac CINE images were acquired in 6 healthy volunteers for sequence optimization and 7 patients who had tumors abutting the heart using a balanced Steady-state free precession (bSSFP) cine sequence on a MRI-guided radiotherapy system. For the patient study, cardiac CINE MRI was acquired immediately after standard pretreatment 3D bSSFP acquisition. A Physiological Monitoring Unit (PMU) was used to acquire ECG signal to gate cardiac CINE MRI acquisition. Each cine imaging slice was acquired in a 10-second breath-hold for 20 cardiac phases.

Results: In the patient study, left ventricular myocardium was contoured at diastolic and systolic phases for each patient and the doses were compared. Due to cardiac motion, substantial dose difference in left ventricular myocardium was observed between the diastolic and the systolic cardiac phases. On average, for the left ventricular myocardium, approximately 10% increase in mean dose and 37% increase in V25Gy were observed in the diastolic phase compare to the systolic phase.

Conclusion: We demonstrated that cardiac bSSFP cine MRI is feasible at the low-field strength of 0.35T on MR guided RT system. Taking cardiac motion into consideration may bring value to better understanding cardiac toxicity relative to the actual dose of the myocardium and other critical cardiac structures.


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