Using FFF beams to improve the therapeutic ratio of lung SBRT

Abstract

Aim: The aim of this study was to investigate the extent to which lung stereotactic body radiotherapy (SBRT) treatment plans can be improved by replacing conventional flattening filter (FF) beams with flattening filter-free (FFF) beams. Materials and methods: We selected 15 patients who had received SBRT with conventional 6-MV photon beams for early-stage lung cancer. We imported the patients’ treatment plans into the Eclipse 13·6 treatment planning system, in which we configured the AAA dose calculation model using representative beam data for a TrueBeam accelerator operated in 6-MV FFF mode. We then created new treatment plans by replacing the conventional FF beams in the original plans with FFF beams. Results: The FFF plans had better target coverage than the original FF plans did. For the planning target volume, FFF plans significantly improved the D98, D95, D90, homogeneity index and uncomplicated tumour control probability. In most cases, the doses to organs at risk were lower in FFF plans. FFF plans significantly reduced the mean lung dose, V10, V20, V30, and normal tissue complication probability for the total lung and improved the dosimetric indices for the ipsilateral lung. For most patients, FFF beams achieved lower maximum doses to the oesophagus, heart and the spinal cord, and a lower chest wall V30. Conclusions: Compared with FF beams, FFF beams achieved lower doses to organs at risk, especially the lung, without compromising tumour coverage; in fact, FFF beams improved coverage in most cases. Thus, replacing FF beams with FFF beams can achieve a better therapeutic ratio.

Evaluation of flattening-filter-free and flattening filter dosimetric and radiobiological criteria for lung SBRT: A volume-based analysis

“…According to the RTOG 0813 recommendation ( 18 ), all of the SBRT plans had D 1500cc <12.5 Gy, D 1000cc <13.5 Gy and V 20 <10%. The use of FFF beams in lung SBRT treatment has been previously studied ( 6 , 15 , 30 ). Pokhrel et al.…”

“…Similarly, Vassiliev et al. ( 30 ) investigated dosimetric differences between FFF beams and FF beams, and reported that FFF beams achieved significantly better target coverage and OAR-sparing than FF beams. This dosimetric advantage of FFF beams was due to the lower out-of-field dose, more rapid dose fall-off, and softer energy spectrum removing the flattening filter compared to FF beams ( 31 ).…”

Monte Carlo evaluation of target dose coverage in lung stereotactic body radiation therapy with flattening filter-free beams

“…The local control rate was 100% and none of the patients developed acute lung or rib toxicity. In a treatment planning study, Vassiliev et al 2 investigated lung SBRT treatments with 6-MV FF and 6-MV FFF beams for 15 patients. For the PTV, FFF plans improved several parameters: D 98 , D 95 , D 90 , the homogeneity index (HI), and uncomplicated tumour control probability (UTCP).…”

“…A complete dosimetric analysis of the new FFF plans is given elsewhere. 2 The main finding was that by using FFF beams, doses to organs at risk could be lowered without compromising tumour coverage.…”

“…Monte Carlo calculations of dose distributions in a simple geometric phantom, 1 and a treatment planning study 2 showed that using FFF beams can improve the therapeutic ratio in lung SBRT. This study is an extension of that prior work.…”