Lung Stereotactic Body Radiation Therapy Using Dynamic Conformal Arc Therapy With or Without Flattening Filter Photon Beam: A French Institutional Experience.

Purpose: To evaluate the safety and efficacy of the flattening filter-free (FFF) technique compared with the flattening filter (FF) technique in the context of lung tumor stereotactic body radiation therapy (SBRT).

Methods and materials: The study included a total of 101 lung SBRT treatments among 82 consecutive patients. Patients were treated with an FF technique (FF group, n = 47) between 2012 and 2014 and with an FFF technique (FFF group, n = 54) between 2014 and 2016. Our risk-adapted SBRT fractionation protocol based on location (3 or 5 fractions) remained unchanged during the entire study. Treatment plans consisted of a dynamic conformal half-arc, and the dose was prescribed to the 80% isodose line. FFF treatments are delivered 2.33 times faster than FF treatments because of the higher dose rate of the machine.

Results: The median follow-up for the 82 patients was 55.4 months, and the median overall survival for all patients was 45.9 months. Local control at 2 years post-SBRT of the 101 lesions was excellent and similar in both groups (97.9% in the FF group vs 98.1% in the FFF group). There were no grade 4 or 5 toxicities and only 4 grade 3 lung toxicities (4.1%) in the FF group (vs none in the FFF group). Three patients in the FFF group versus 1 patient in the FF group had a symptomatic rib fracture. Among patients treated free breathing on a single lesion (n = 65), the local recurrence-free survival at 2 years was 85.7% (95% CI, 62.0-95.2) in the FFF group and 71.4% (95% CI, 52-84.1) in the FF group (P = .139).

Conclusions: Patient treatment with lung SBRT using the FFF technique is safe and provides an excellent long-term local control and low toxicity compared with the FF technique.