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

Tobias Finazzi; John R van Sörnsen de Koste; Miguel A Palacios; Femke O B Spoelstra; Berend J Slotman; Cornelis J A Haasbeek; Suresh Senan

doi:10.1016/j.phro.2020.05.002

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

Phys Imaging Radiat Oncol. 2020 May 20:14:17-23. doi: 10.1016/j.phro.2020.05.002. eCollection 2020 Apr.

Authors

Tobias Finazzi¹, John R van Sörnsen de Koste¹, Miguel A Palacios¹, Femke O B Spoelstra¹, Berend J Slotman¹, Cornelis J A Haasbeek¹, Suresh Senan¹

Affiliation

¹ Department of Radiation Oncology, Amsterdam University Medical Centers, Location VUmc, de Boelelaan 1117, 1081 HV Amsterdam, The Netherlands.

Abstract

Background and purpose: 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.

Materials and methods: 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 (GTV_t) 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.

Results: 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 GTV_t 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 GTV_t coverage was not influenced due to real-time MR-guidance. On-table adaptation improved PTV coverage, but had limited impact on GTV doses.

Conclusions: 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.

Keywords: Adaptive radiotherapy; Lung cancer; MR-guided radiation therapy; SABR; Single-fraction.