Speaker
Description
Purpose: The flattening filter free (FFF) mode (Elekta) was recently installed at our institution. We investigated FFF planning and delivery for stereotactic peripheral lung treatment as the increased dose rate of FFF mode can reduce the treatment time.
Methods: Ten lung cancer patients with peripheral lesions previously treated with VMAT SBRT were selected to span a range of target sizes and locations. Three additional plans were created for each patient: two 3D conformal plans with 6 MV conventional flattening filter (cFF) and FFF beams, and a VMAT plan with 6 MV FFF. Beam on time was measured for the VMAT plans and estimated for the 3D conformal plans.
Results: FFF VMAT plans met our institutional planning criteria with no or minimal changes to the optimization parameters. The FFF VMAT plans required 5.0 minutes less (median) delivery time (range 2.3 to 10.1 min) compared to cFF VMAT plans. The median effective dose rate for cFF VMAT was 533 MU/min (range 510-562) and for FFF VMAT was 1144 MU/min (range 934-1406) compared to maximum dose rates of 590 MU/min and 1550 MU/min respectively. FFF conformal plans met planning criteria and had an estimated median time savings of 2.5 min (range 2.0-3.3) compared to conformal plans using the cFF beam.
Conclusions: Acceptable peripheral lung SBRT plans can be produced with the FFF beam using both 3D conformal and VMAT techniques. Median time savings of 5.0 and 2.5 minutes for VMAT and 3D conformal plans were achieved compared to using the cFF beam.
