Flattening filter-free technique in volumetric modulated arc therapy for lung stereotactic body radiotherapy: A clinical comparison with the flattening filter technique

Abstract

The present study sought to evaluate the impact of the flattening filter-free (FFF) technique in volumetric modulated arc therapy for lung stereotactic body radiotherapy. Its clinical safety and availability were compared with the flattening filter (FF) method. The cases of 65 patients who underwent lung volumetric modulated arc therapy-stereotactic body radiotherapy (VMAT-SBRT) using FF or FFF techniques were reviewed. A total of 55 Gy/4 fractions (fr) was prescribed for peripheral lesions or 56 Gy/7 fr for central lesions. The total monitor units (MU), treatment time, dose to tumors, dose to organs at risk, tumor control (local control rate, overall survival, progression-free survival) and adverse events between cases treated with FF and cases treated with the FFF technique were compared. A total of 35 patients were treated with conventional FF techniques prior to November 2014 and 30 patients were treated with FFF techniques after this date. It was revealed that the beam-on time was significantly shortened by the FFF technique (P<0.01). Other factors were similar for FFF and FF plans in respect to conformity (P=0.95), homogeneity (P=0.20) and other dosimetric values, including total MU and planning target volume/internal target volume coverage. The median follow-up period was 18 months (range, 2-35). One-year local control rates were 97.1 and 90.0% in the FF group and FFF groups, respectively (P=0.33). Grade 3 pneumonitis was observed in 5.8% of FF patients and 3.4% of FFF patients (P=1.00). No other adverse events ≥grade 3 were observed. The results of the study suggest that VMAT-SBRT using the FFF technique shortens the treatment time for lung SBRT while maintaining a high local control rate with low toxicity.

Keywords: flattening filter-free; lung cancer; radiation pneumonitis; stereotactic body radiotherapy; volumetric modulated arc therapy.

Figure 1.

Radiation dose distribution of SBRT using intensity modulated radiation therapy method called single-arc volumetric modulated arc therapy.

Figure 2.

Box-plot diagrams about the treatment time of the FF and FFF groups.

Figure 3.

Kaplan-Meier curves illustrating overall survival for patients treated using FF technique (black line) and FFF technique (red line).

Figure 4.

Kaplan-Meier curves for relapse-free survival (RFS) for patients treated using FF technique (black line) and FFF technique (red line).

Figure 5.

Kaplan-Meier curves for local control rate (LCR) for patients treated using FF technique (black line) and FFF technique (red line).

Figure 6.

In this case of primary lung cancer located in the left upper lobe, local recurrence occurred 7 months and brain metastasis occurred 11 months after SBRT (55 Gy/4Fr) was performed. (A) Primary lung lesion before treatment, (B) PET-CT image of brain before SBRT, (C) local recurrence 7 months after SBRT, (D) brain metastasis 11 months after SBRT.

Figure 7.

A case of grade 2 bronchial stenosis in an FFF subject. This case received VMAT-SBRT of 56 Gy/7fr using FFF technique for central lesions in the right lung. It is obvious that the bronchial lumen indicated by the arrow gradually narrowed after treatment. (A) Before treatment; (B) 3 months after treatment; and (C) 7 months after treatment.