Intensity modulated radiosurgery of brain metastases with flattening filter-free beams

Flattening filter free (FFF) irradiation potentially reduces treatment delivery time in radiosurgery thus eliminating intrafraction motion and increasing patient comfort. We compared plan quality and efficiency of VMAT and IMRT plans for FFF- and standard delivery for brain metastases with single fraction doses of 20 Gy and validated the dosimetric accuracy of the FFF delivery.

CT data of 15 patients with brain metastases were included in this study. For every patient, 2 IMRT- and 2 VMAT-plans were created using a high-resolution MLC with two different delivery modes (6MV standard vs. 6MV FFF). Plan quality and efficiency was assessed by analysis of conformity, homogeneity, dose gradients, treatment delivery time and number of monitor units (MU). Dosimetric evaluation was performed for 10 FFF plans with radiochromic film and ion chamber.

Plan quality was similar for both approaches. FFF provided a mean treatment time reduction of 51.5% with similar MU for VMAT and IMRT for this low-modulation paradigm. The dosimetric validations showed an absolute dose deviation of +0.93 ± 0.99% and γ-index analysis (3%/3mm and 3%/1mm) resulted in agreement of 99.08 ± 1.58% respectively 93.46 ± 2.41%.

FFF radiosurgery is an efficient technique for intensity modulated hypofractionated or single fraction treatments with similar plan quality when compared to flattened beams at reduced treatment time.