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Improving the Treatment Accuracy of Standard Linear Accelerator-Based Pancreatic SBRT: Initial Clinical Experience with An In-House Position Monitoring System

S Arumugam1,2,3*, J Begg1,2,3, N Collier3,4, M Lee3,4, (1) Department of Medical Physics, Liverpool and Macarthur Cancer Therapy Centre, Sydney, Australia, (2) Ingham Institute for Applied Medical Research, Sydney, Australia, (3) South Western Sydney Clinical School, School of Medicine, University of New South Wales, Sydney, Australia, (4) Department of Radiation Oncology, Liverpool and Macarthur Cancer Therapy Centre, Sydney, Australia

Presentations

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

Room: AAPM ePoster Library

Purpose: assess and correct for intrafraction target position deviation during pancreatic stereotactic body radiation therapy (SBRT) using an in-house real-time position monitoring system.

Methods: online image based position monitoring system,SeedTracker,was developed to monitor intrafraction radiopaque marker positions using monoscopic x-ray images, available from the Elekta XVI imaging system.This system was applied to patients receiving SBRT for pancreatic cancer on the MASTERPLAN Pilot trial (UTN: U1111-1202-7476) in South Western Sydney Local Health District, Australia. During treatment delivery the marker positions were compared to expected positions delineated from the planning CT.All patients were implanted with at least four peri-tumoral radiopaque markers prior to SBRT for target localisation. Each patient was planned for SBRT using a dual arc VMAT technique and five treatment fractions to a dose of 30-45Gy. The position tolerance of ±3mm from the expected position of the markers was set to trigger a gating event during treatment . A CBCT was acquired prior to any re-positioning of the patient and corrections made for moves >3mm.

Results: patients received SBRT with real-time intrafraction monitoring using SeedTracker.
2 patients were treated with an exhale breath-hold (EBH) technique, 3 with abdominal compression (AC) and the remaining 3 in free breathing (FB).Gating events and position corrections occurred in 7 of 8 treatment courses. A gating event occurred in 50%, 26% and 33% of total treatment fractions in patients treated with EBH, AC and FB techniques respectively. In patients treated with AC and FB techniques, transient position deviations occurred in 20% of treatment fractions but did not require treatment interruption and position correction.

Conclusion: intrafraction position monitoring of pancreatic SBRT was successfully achieved using an in-house system. The developed system was shown to improve the accuracy of treatment delivery and resulted in corrections in over 80% of SBRT treatments.

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