The effect of FFF for patients receiving pelvic radiotheraphy using vomumetric modulated arc therapy (VMAT) tecnique

In this study, dosimetric data of 10 patients with prostate cancer receiving radiotherapy using intensity modulated radiation theraphy (IMRT) as Volumetric modulated arc therapy (VMAT) technique were studied. Treatment plans were created in ECLIPS treatment planning system (TPS) using 2 arcs VMAT, 10MV energy, 600MU/second dose rates for FF plans and 800MU/second dose rates for FFF plans, inTruebeam-STx linac. Target volumes were PTV1 (prostate), PTV2 (Seminal Vesicle) and PTV3 (pelvic Lymph node) and rectum and bladder were accepted as organ at risk (OAR). For each patient, 2 different plans as used FF and not used FF (FFF) were made and dose distributions were obtained. Maximum dose within targets and OAR, dose homogeneity and conformality for PTV1 target, used MU values for FF and FFF plans were compared. Dmax values were found higher in FFF plans than FF plans, 1.74%, 0.61% and 0.58% for PTV1, PTV2 and PTV3 respectively. Difference was significant for PTV1 (p=0,00) only. Both homogeneity and conformality for PTV1 were more successful in FF in comparison to FFF; difference was significant and 17.6% for homogeneity (p=0,00) and 2.54% for conformality (not significant). Max OAR doses were less FF than FFF, difference was 1.17% for rectum and 0.51% for bladder; difference was significant for rectum (p=0,039) while not significant for bladder. MU values 40% higher for FFF than FF (p=0,00). In conclusion, better conformality, homogeneity and OAR protection were achieved for FF plans in comparison to FFF plans while higher MU required for FFF plans.