A dosimetric dnalysis of flattening-filter-free mode linear accelerator-based stereotactic body radiation therapy and HDR brachytherapy for prostate cancer

Abstract

Purpose: Prior studies have reported that linear accelerator (LINAC)-based stereotactic body radiation therapy (SBRT) plans for prostate cancer are unable to achieve comparable intraprostatic doses to high-dose-rate brachytherapy (HDR). However, the utilization of flattening-filter-free (FFF) beams provides superior dose distributions compared with flattened beams. The purpose of this study was to test the feasibility of achieving the high intraprostatic doses observed in HDR by utilizing LINAC - based SBRT with FFF beams. Methods: We randomly selected 10 patients with localized prostate cancer previously treated at our institution in 2013. FFF-mode LINAC-based SBRT and simulated HDR (using virtual HDR catheters) plans were generated for each patient. The planning target volume (PTV) V100, V125, V150 and V200 values were compared between the two plans using the two-sided paired samples t-test. Results: Regarding the PTV coverage, the mean V100 was slightly higher for SBRT at 96.47% compared with 94.68% for HDR (p = 0.003). The V125 (61.69% versus 66.51%, p = 0.004) and V200 (15.06% versus 19.66%, p < 0.001) were slightly lower for SBRT. There were no significant differences in V150 between the two plans (47.59% versus 49.8%, p = 0.375). Rectal and bladder dosimetry were also comparable between the two modalities, though the rectal maximum dose was lower in the SBRT plan (99.6% versus 103.66%, p = 0.006) and the dose to 15cc of bladder was lower in the HDR plan (96.34% versus 78.18%, p = 0.005). Conclusion: Utilization of FFF mode LINAC-based SBRT allows for achievable dosimetry that is very similar to high dose rate brachytherapy. Further studies are warranted regarding the safety and efficacy of this modality.