Dosimetric comparison of stereotactic body radiation therapy plans for spine metastasis using flattening filter free and flattening filter modes

Objective: To compare the dosimetric difference of stereotactic body radiation therapy (SBRT) plans for spine metastasis using 6 MV X-ray flattening filter free (FFF) and flattening filter (FF) modes. Methods: A total of nine previously treated patients with a total of twelve spine metastasis were retrospectively included and replanned using FFF-SBRT and FF-SBRT, respectively. The dose-volume histograms (DVH), target conformity index (CI), monitor unites (MUs) and treatment time of target volume, organs at risk and normal tissues were compared between the plans. Results Both FFF-SBRT and FF-SBRT met the clinical objectives. Dose distribution of target volume, organs at risk and normal tissues were similar. MUs of the FFF-SBRT were significantly higher than that of FF-SBRT (t = -5.20, P < 0.01), while the treatment time was almost half of the latter (t = 17.27, P < 0.01). Conclusions: Two plan modes are both clinically acceptable. FFF-SBRT plans are delivered in less time and with better efficiency. Trial registration Chinese clinical trial registry, ChiCTR-TRC-14004281. (authors)