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Tumor Position Variation in Gating Window Using Cine MRI of 0.35T MRgRT

A Guta1*, B Lewis1,Z Ji1 D Lam1,T Mazur1, S Mutic1 and T Kim1 (1) Washington University in St. Louis, St Louis, Mo

Presentations

(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

Room: AAPM ePoster Library

Purpose: Correlation between tumor and diaphragm positions is a key component in x-ray imaging-guided radiotherapy. Tumor position with respect to the diaphragm was extracted from cine MR images obtained on 0.35T MRgRT systems and tumor position variation in gating windows was evaluated.


Methods: Cine MRI of 675 fractions for lung cancer treatments and 100 fractions for pancreatic cases were pulled out from the clinical database, retrospectively. We developed in-house software to extract tumor position with respect to diaphragm position from cine MR images. Diaphragm positions were determined using a template-based auto-segmentation method and tumor positions were extracted from target contours determined by the MRgRT systems. Each diaphragm contour was manually evaluated and adjusted. In total, 6713 images of cine MRI from 10 fractions for lung cases and 2 fractions for pancreatic cases were processed. Tumor position variation within the following gating windows was evaluated: full amplitude, 20% end of inhalation (EOI), 10% of EOI, 20% end of exhalation (EOE) and 10% EOE.


Results: For lung cancer patients, tumor position varied by 10.7, 8.4, 16.7, and 17.0mm in the anterior, posterior, superior, and inferior directions respectively, over the full amplitude of the respiratory cycle. In the superior direction the tumor moved on average (SD) 6.6(4.2), 2.9(2.4), 5.3(4.3), and 3.5(2.7)mm for the 20% EOI, 10% EOI, 20% EOE, and 10% EOE respectively, and moving inferiorly 7.4(4.5), 3.2(2.7), 6.8(5.1), and 3.9(2.6)mm for the same gating windows. Over the full respiratory amplitude, pancreas tumors moved 9.4, 6.0, 16.2, and 11.3mm in the anterior, posterior, superior, and inferior directions, respectively.


Conclusion: We presented that tumor position variation was reduced by gating window size but within standard deviation, indicating further consideration to target margin determination. The on-going study will provide statistical analysis of tumor position variation with respect to diaphragm.

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Keywords

MRI

Taxonomy

IM/TH- MRI in Radiation Therapy: MRI/Linear accelerator combined- IGRT and tracking

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