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Image-Guided Margin Assessment to LINAC-Based Radiosurgery for Single and Multiple Brain Metastases Based On Post-Treatment CBCT Shifts

T Reynolds*, M Ozer, Minnesota Oncology, Maplewood, MN

Presentations

TU-D1030-IePD-F6-1 (Tuesday, 7/12/2022) 10:30 AM - 11:00 AM [Eastern Time (GMT-4)]

Exhibit Hall | Forum 6

Purpose: The purpose of our study is to provide image-guided margin assessment based on post-treatment cone beam CT (CBCT) shifts and its dosimetric impact to target coverage for single and multiple brain metastases (BM) patients.

Methods: 55 patients with total of 117 BM, receiving stereotactic radiosurgery (SRS), were retrospectively evaluated. All patients were immobilized with the Encompass device (Qfix) and planned with HyperArc technique. The plans consisted of 52 single, and 17 multiple BM (lesions number ranging from 2 to 7) plans. All multiple BM targets were within 6 cm of the planning isocenter. In total, 120 single and 72 multiple BM plans were evaluated based on post-treatment CBCTs. To evaluate target coverage loss due to intrafraction motion, MIM software was used. Shifts from post-treatment CBCTs were applied to planning CT, and PTV/GTV dosimetric coverage was evaluated.

Results: To evaluate target coverage loss due to intrafraction motion, 117 single BM were considered. Of those, 25(21%) patients had 0-1-mm margin and 92(79%) patients had 2-mm PTV margin. The significant loss of the target coverage was observed in PTVs and GTVs in patients with 0-1-mm margin. The maximum target coverage losses were as high as 40% for PTV, and 28% for GTV with the mean target loss of 10.57±8.80% for PTVs, 6.51±8.16% for GTV. In comparison, plans with 2-mm margin showed maximum PTV target coverage loss of 16%, and mean of 4.14±3.34%. GTV losses in this group was maximum of 1% with mean value of 0.04±0.11%. For all multiple metastases BM patients, a 2-mm margin was used and no significant GTV coverage loss was noted.

Conclusion: This study demonstrates that a 2-mm margin is adequate for treating single and multiple BM patients using single isocenter LINAC-based SRS based on post-treatment CBCT shifts analysis of the target coverage loss due to intrafraction motion.

Keywords

Radiosurgery, Cone-beam CT

Taxonomy

IM/TH- Image-guided Surgery: CT/CBCT-guided surgery

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