Comparison of flattening filter applied and not applied intensity modulated radiation therapy plans in prostate cancer

Comparison of Flattening Filter Applied and Not Applied Intensity Modulated Radiation Therapy Plans in Prostate Cancer. Removing flattening filter (FF) from linac cause increasing dose rate while decreasing peripheral dose. This study investigate FF applied and not applied (FFF) Intensity-Modulated Radiation Therapy (IMRT) plans, in patients with prostate cancer receiving radiotherapy using 10MV, Truebeam-STx linac. Target volumes were PTV1 (prostate), PTV2 (seminal vesicle); organ at risk (OAR) were rectum and bladder. Dose distribution?s obtained from FF and FFF for targets and OAR were compared. Furthermore, effect of FFF on MU, homogeneity and conformality for PTV1 examined. Hot spot dose within PTV1 and PTV2 targets were significantly greater for FFF in comparison to FF (p=0.031 for PTV1, p=0.00 for PTV2); however, differences for both volumes were limited to 1%. Likewise hot spot dose for OAR was significantly greater for FFF then FF. There were 1% difference for both rectum volume within target and rectum volume not included by target (p=0.009, p=0.008). Hot spot dose was 4.31% higher for FFF then FF for bladder included by target, but difference was not significant (p=0.301). Hot spot dose in FFF was significantly higher in bladder volume not included by target (p=0.00), but difference was 0.8%. Homogeneity was better for FFF then FF; however the difference was 5% and not significant (p=0.815). Dose conformality was significantly more successful for FF then FFF (p=0.001), difference was 6.84%. MU values 20% higher for FFF in comparison to FF and significant (p=0.00). Results of this study suggest that better conformality and OAR protection were achieved in FF plans then FFF using less MU values.