Single-fraction flattening filter-free volumetric modulated arc therapy for lung cancer: Dosimetric results and comparison with flattened beams technique

Purpose: To report on single-fraction stereotactic body radiotherapy (RT) (SBRT) with flattening filter (FF)-free (FFF) volumetric modulated arc therapy (VMAT) for lung cancer and to compare dosimetric results with VMAT with FF. Methods and materials: Overall, 25 patients were treated with 6-MV FFF VMAT (Varian TrueBeam STx LINAC) to a prescribed dose of 24. Gy in a single fraction. Treatment plans were recreated using FF VMAT. Dose-volume indices, monitor units (MU), and treatment times were compared between FFF and FF VMAT techniques. Results: Dose constraints to PTV, spinal cord, and lungs were reached in FFF and FF plans. In FFF plans, average conformity index was 1.13 (95% CI: 1.07 to1.38). Maximum doses to spinal cord, heart, esophagus, and trachea were 2.9. Gy (95% CI: 0.4 to 6.7. Gy), 0.8. Gy (95% CI: 0 to 3.6. Gy), 3.3. Gy (95% CI: 0.02 to 13.9. Gy), and 1.5. Gy (95% CI: 0 to 4.9. Gy), respectively. Average V7. Gy, V7.4. Gy, and mean dose to the healthy lung were 126.5. cc (95% CI: 41.3 to 248.9. cc), 107.3. cc (95% CI: 18.7 to 232.8. cc), and 1.1. Gy (95% CI: 0.3 to 2.2. Gy), respectively. No statistically significant differences were found in dosimetric results and MU between FF and FFF treatments. Treatment time was reduced by an average factor of 2.31 (95% CI: 2.15 to 2.43) from FF treatments to FFF, and the difference was statistically significant. Conclusions: FFF VMAT for lung SBRT provides equivalent dosimetric results to the target and organs at risk as FF VMAT while significantly reducing treatment time.