Nov 21 – 22, 2019
Paul Scherrer Institute
Europe/Zurich timezone
A WARM WELCOME in VILLIGEN

Motion management and dose reconstruction for MRI guided cardiac radiosurgery

Speaker

Stefanie EHRBAR (Radiation Oncology Department, Universitätsspital Zürich, Switzerland)

Description

Purpose: To evaluate the dosimetric effect of the residual breathing motion during gating for the first patient treated with MRI guided cardiac radiosurgery.

Methods: A patient with ventricular tachycardia was treated in one fraction with a dose of 25 Gy to the 85%-isodose line to the planning target volume (PTV). The target volume (TV) was defined according to the cardiologists interpretation of the electrophysiological mapping of the arrhythmic substrat and expanded by 2 mm axially and 3 mm craniocaudally to the PTV. The patient was treated with the MRIdian system (Viewray). A mix of instructed breath-hold and free-breathing was performed, while a structure close to the diaphragm was tracked for respiratory gating at end of-exhale using sagittal 2D cine-MR with 4 fps. A gating window of 5 mm was defined and maximal 20% of the structure were allowed outside of the window for irradiation. The residual motion during gating was evaluated in the two directions (SI and AP) and a 2mm-binned position-probability map was generated. The dose to the patient was recalculated for each possible combination of SI- and AP-shift and summed with the weighting of the probability map.

Results: In total, 46 min of cine-MR were recorded for treatment and the target was within the gating window for 24 min. Thereof, 14 min were in breath-hold (>=10 s, 55 holds) and 10 min in free-breathing (<10 s, 257 breaths). The mean 2D offset could be reduced from 6.8 mm to 3.7 mm with gating. The reconstructed dose distribution showed a TV Dmean of 27.6 Gy (planned: 27.8 Gy) and D95 of 26.3 Gy (planned: 27 Gy). Organs at risk did not show any increase in dose, expect for the bronchial tree with a Dmean of 2.5 Gy (planned: 1.6 Gy).

Conclusion: MRI guided cardiac radiosurgery was successfully applied. With the motion tracking and gating, the patient could be treated with a good coverage of the target volume and minimal dose to organs at risk.

Primary author

Stefanie EHRBAR (Radiation Oncology Department, Universitätsspital Zürich, Switzerland)

Co-authors

Dr Stephanie TANADINI-LANG (Radiation Oncology Department, Universitätsspital Zürich, Switzerland) Mr Michael MAYINGER (Radiation Oncology Department, Universitätsspital Zürich, Switzerland) Ms Madalyne CHAMBERLAIN (Radiation Oncology Department, Universitätsspital Zürich, Switzerland) Prof. Nicolaus ANDRATSCHKE (Radiation Oncology Department, Universitätsspital Zürich, Switzerland)

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