IFI (intra-fractional imaging) on Elekta linacs allows the concurrent acquisition of Cone Beam CT (CBCT) during VMAT treatment delivery. The image quality is reduced from CBCT alone due to scatter of the MV treatment beam onto the kV panel. Stereotactic radiation treatments (SRT) are long due to the high dose per fraction and multiple imaging scans required, this can be challenging particularly for patients with advanced disease.
The advantage of using IFI is in treatment efficiency if it can replace mid or post-treatment CBCTs.
Assess the role of IFI in reducing treatment duration for patients undergoing treatment for metastatic disease with SRT using image registration to bony structures.
From Jan- Sept 2024, 100 IFIs were taken during the stereotactic treatment of patients with brain, spine and other oligo metastases for which a bony image match had been deemed appropriate. For patients with solitary or multiple (but separately treated) brain metastases, a single IFI was scheduled for their first fraction. For patients receiving mono-isocentre multi-site brain SRT, IFI was acquired for each fraction on all treatment beams instead of mid and post-CBCTs. Patients undergoing SRT for spinal metastases received two IFI images each fraction (mid and post-CBCT), and patients treated for other metastases would receive an IFI each fraction in-place of a post-CBCT.
Only one of the 100 IFIs had image quality that wasn’t good enough for matching to bony structures. One pre-treatment CBCT image quality was poor so no IFI was acquired.
99 CBCTs were not required equating to approximately one hour of treatment time over a duration of 9 months. The largest time saving was for patients with multiple treatment beams.
IFI can be successfully used to reduce the time patients with advanced disease spend on the treatment couch.