Delivery of magnetic resonance-guided single-fraction stereotactic lung radiotherapy

•MR-guidance enables high precision single-fraction lung SABR delivery.•Breath-hold gating resulted in a mean tracked GTVt coverage of 99.6% during beam-on.•On-table plan adaptation improved PTV coverage, but had little impact on GTV doses.•Improved techniques are needed to allow for consistent MR-t...

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Published in:Physics and imaging in radiation oncology Vol. 14; pp. 17 - 23
Main Authors: Finazzi, Tobias, van Sörnsen de Koste, John R., Palacios, Miguel A., Spoelstra, Femke O.B., Slotman, Berend J., Haasbeek, Cornelis J.A., Senan, Suresh
Format: Journal Article
Language:English
Published: Netherlands Elsevier B.V 01.04.2020
Elsevier
Subjects:
Adaptive radiotherapy
Lung cancer
MR-guided radiation therapy
Original
SABR
Single-fraction
SABR
MR-guided radiation therapy
Single-fraction
Lung cancer
Adaptive radiotherapy
ISSN:2405-6316, 2405-6316
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Summary:•MR-guidance enables high precision single-fraction lung SABR delivery.•Breath-hold gating resulted in a mean tracked GTVt coverage of 99.6% during beam-on.•On-table plan adaptation improved PTV coverage, but had little impact on GTV doses.•Improved techniques are needed to allow for consistent MR-tracking of small tumors. Single-fraction stereotactic ablative radiotherapy (SABR) is an effective treatment for early-stage lung cancer, but concerns remain about the accurate delivery of SABR in a single session. We evaluated the delivery of single-fraction lung SABR using magnetic resonance (MR)-guidance. An MR-simulation was performed in 17 patients, seven of whom were found to be unsuitable, largely due to unreliable tracking of small tumors. Ten patients underwent single-fraction SABR to 34 Gy on a 0.35 T MR-linac system, with online plan adaptation. Gated breath-hold SABR was delivered using a planning target volume (PTV) margin of 5 mm, and a 3 mm gating window. Continuous MR-tracking of the gross tumor volume (GTVt) was performed in sagittal plane, with visual patient feedback provided using an in-room monitor. The real-time MR images were analyzed to determine precision and efficiency of gated delivery. All but one patient completed treatment in a single session. The median total in-room procedure was 120 min, with a median SABR delivery session of 39 min. Review of 7.4 h of cine-MR imaging revealed a mean GTVt coverage by the PTV during beam-on of 99.6%. Breath-hold patterns were variable, resulting in a mean duty cycle efficiency of 51%, but GTVt coverage was not influenced due to real-time MR-guidance. On-table adaptation improved PTV coverage, but had limited impact on GTV doses. Single-fraction gated SABR of lung tumors can be performed with high precision using MR-guidance. However, improvements are needed to ensure MR-tracking of small tumors, and to reduce treatment times.
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Authors responsible for statistical analysis: Tobias Finazzi, John R. van Sörnsen de Koste.
ISSN:2405-6316
2405-6316
DOI:10.1016/j.phro.2020.05.002