Initial experience delivering stereotactic radiotherapy to a gluteal metastasis on a 1.5T MR Linac
Amaro, P. T. McDaid, Lisa Davies, Lucy Whiteside, Lee Clough, Abigael Faivre-Finn, Corinne Parker, Jacqui Bailey, Rachael Benson, Rebecca Nelder, Claire L
Amaro, P. T.
McDaid, Lisa
Davies, Lucy
Whiteside, Lee
Clough, Abigael
Faivre-Finn, Corinne
Parker, Jacqui
Bailey, Rachael
Benson, Rebecca
Nelder, Claire L
Citations
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Abstract
Purpose or Objective
This work reports on our initial experience delivering stereotactic ablative radiotherapy (SABR) to a gluteal metastasis on
a 1.5T Elekta Unity MR Linac (MRL) (Elekta AB. Stockholm, Sweden).
Materials and Methods
A patient with non-small cell lung cancer (NSCLC) was found to have an 8mm right-sided gluteal oligometastasis on staging
FDG PET-CT (stage IVa, oligometastatic disease). Discussion at local SABR multi-disciplinary team (MDT) highlighted
challenges in localising the sub-centimetre gluteal metastasis on cone-beam CT (CBCT) imaging, therefore a referral was
made for treatment on the MRL within the ethically approved, imaging study PRIMER (Clinicaltrials.gov NCT02973828).
A preliminary MR scan was performed to ensure the lesion was identifiable. Vendor approved MR sequences (Table 1) were
used to determine lesion conspicuity as, ultimately, only these sequences are sanctioned for clinical use on the Unity MRL.
A further spectrally selective attenuated inversion recovery (SPAIR) sequence was performed to suppress fat signal and
provide further confidence in disease visibility. The patient then underwent CT and MR planning scans (pCT and pMR
respectively), positioned supine with arms on thorax and pelvis immobilised with knee and foot step. pCT was performed
for the provision of electron density data to inform treatment planning.
pCT and pMR image sets were imported into the Monaco treatment planning system (v 5.40.01, Elekta AB. Stockholm,
Sweden) for target volume and organ at risk (OAR) delineation and a prescription of 30Gy in 3 fractions was planned. The
T2 SPAIR sequence was co-registered with the 6 minute T2 3D Tra sequence to further aid target delineation. Results
Delivery of SABR (30Gy in 3 fractions over 6 days) to a gluteal oligometastasis was successfully completed on the Unity MRL
following the Adapt to Position (ATP) workflow. Target visualisation on pMR was superior to pCT, in which the 8mm lesion
was barely visible (Figure 1). Consensus review showed that the 6 minute T2 3D Tra sequence provided superior confidence
in target visibility and was therefore used for planning and daily plan adaptation/verification. Median treatment time was
52:08 (range 49:19 - 57:16). The patient did not report any adverse effects. Conclusion
We have successfully completed SABR delivery to a sub-centimetre oligometastasis within the right gluteus medius muscle
on the Elekta Unity MRL following the ATP workflow, a first at our institution. This would not have been possible on a
conventional linac due to the poor soft-tissue contrast associated with CT and CBCT imaging. Workflows have been
established that will facilitate a future MR guided, soft tissue tumour service.
Description
Date
2022
Publisher
Collections
Keywords
Type
Meetings and Proceedings
Citation
Amaro PT, McDaid L, Davies L, Whiteside L, Clough A, Faivre-Finn C, et al. Initial experience delivering stereotactic radiotherapy to a gluteal metastasis on a 1.5T MR Linac. Radiotherapy and Oncology. 2022 May;170:S1662-S3. PubMed PMID: WOS:000806779900695.