Efficiency of Real-Time Monitored SBRT for Accelerated Partial Breast Irradiation (APBI) Using 3D Bioabsorbable Marker
S Shen1*, C Veale1, E Thomas2, M Bredel1, K Keene1, M Dobelbower1, H Krontiras1, H Boggs1, (1) University of Alabama Birmingham, Birmingham, AL, (2) The Ohio State University
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PO-GePV-M-199 (Sunday, 7/10/2022) [Eastern Time (GMT-4)]
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Purpose: Real-time respiratory motion monitoring with implanted fiducials (image trigger) improves confidence in target dose delivery. This study evaluates delivery efficiency for SBRT APBI patients using a 3D bioabsorbable marker (spiral framework embedded with 6 titanium clips for surgical excision site).
Methods: 13 early-stage breast cancer patients were treated with SBRT APBI in 2021. All patients received 30 Gy in 5 fractions, using 10X-FFF, 2 VMAT arcs (n=11), or 9-field IMRT (n=2). Setup-imaging included orthogonal kV and CBCT images prior to treatment. During treatment, real-time kV images were triggered by gantry motion (10°) for VMAT; or by time (3 sec) for 9-field IMRT. 12 patients were treated with free-breathing, 1 patient was treated with breath-hold. PTV was a 3 mm expansion from CTV. Beams were put “on-hold” when fiducial marker excursions exceeded 3 mm.
Results: Among 55 treatment sessions for 11 patients with VMAT, median time for beam start-to-end was 1.9 (range 1.5-5.3) min, median time from starting setup-imaging to beam-end was 9.1 (range 5.9-16.6) min. 7 out of 55 sessions had beam “on-hold” because fiducial excursions exceeded 3 mm. The added time due to beam “on-hold” was not remarkable when compared to other treatment sessions without beam “on-hold” for the same patient. 3 out of 55 sessions re-acquired orthogonal kV for re-positioning, with added time within 3.4 min. Among 10 treatment sessions for 2 patients with 9-field IMRT, median time for beam start-to-end was 4.4 (range 3.5-8.4) min, median time from starting setup-imaging to beam-end was 13.3 (range 9.6-25.9) min.
Conclusion: Using 3D bioabsorbable marker, real-time monitored SBRT APBI improved confidence in target dose delivery (within 3 mm excursion) with patients in free-breathing. The treatment delivery was efficient.
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