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. 2024 Feb 15:45:100744.
doi: 10.1016/j.ctro.2024.100744. eCollection 2024 Mar.

Stereotactic body radiotherapy of central lung tumours using a 1.5 T MR-linac: First clinical experiences

L G Merckel  1 , J Pomp  1 , S L Hackett  1 , A L H M W van Lier  1 , M van den Dobbelsteen  1 , M J A Rasing  1 , F A A Mohamed Hoesein  2 , L M W Snoeren  1 , C A van Es  1 , P S N van Rossum  1 , M F Fast  1 , J J C Verhoeff  1
Affiliations

Stereotactic body radiotherapy of central lung tumours using a 1.5 T MR-linac: First clinical experiences

L G Merckel et al. Clin Transl Radiat Oncol. .

Abstract

Background: MRI-guidance may aid better discrimination between Organs at Risk (OARs) and target volumes in proximity of the mediastinum. We report the first clinical experiences with Stereotactic Body Radiotherapy (SBRT) of (ultra)central lung tumours on a 1.5 T MR-linac.

Materials and methods: Patients with an (ultra)central lung tumour were selected for MR-linac based SBRT treatment. A T2-weighted 3D sequence MRI acquired during free breathing was used for daily plan adaption. Prior to each fraction, contours of Internal Target Volume (ITV) and OARs were deformably propagated and amended by a radiation oncologist. Inter-fractional changes in volumes and coverage of target volumes as well as doses in OARs were evaluated in offline and online treatment plans.

Results: Ten patients were treated and completed 60 Gy in 8 or 12 fractions. In total 104 fractions were delivered. The median time in the treatment room was 41 min with a median beam-on time of 8.9 min. No grade ≥3 acute toxicity was observed. In two patients, the ITV significantly decreased during treatment (58 % and 37 %, respectively) due to tumour shrinkage. In the other patients, 81 % of online ITVs were within ±15 % of the volume of fraction 1. Comparison with the pre-treatment plan showed that ITV coverage of the online plan was similar in 52 % and improved in 34 % of cases. Adaptation to meet OAR constraints, led to decreased ITV coverage in 14 %.

Conclusions: We describe the workflow for MR-guided Radiotherapy and the feasibility of using 1.5 T MR-linac for SBRT of (ultra) central lung tumours.

Keywords: (Ultra) central lung tumour; MR-Linac; SBRT.

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Conflict of interest statement

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Figures

Fig. 1
Fig. 1
Duration of MRI-guided lung SBRT workflow clockwise starting with pre-treatment MR imaging. The PVMRI and IntraMRI were acquired in parallel with other workflow steps and did not require additional time.
Fig. 2
Fig. 2
Online MRI and physical dose distribution of a patient with a mediastinal lymph node metastasis of a SCLC in whom a 58 % decrease in ITV occurred. The dose distribution of the original plan is projected on the reduced target size at the 12th fraction The ITV (inner green line) and OARs (oesophagus, trachea, spinal cord) within a 3 cm expansion (yellow) around the ITV were modified each fraction by a radiation oncologist.
See this image and copyright information in PMC

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