Volumetric modulation arc radiotherapy with flattening filter-free beams compared with conventional beams for nasopharyngeal carcinoma:a feasibility study

There is increasing interest in the clinical use of flattening filter-free(FFF) beams.In this study,we aimed to investigate the dosimetric characteristics of volumetric modulated arc radiotherapy(VMAT) with FFF beams for nasopharyngeal carcinoma(NPC).Ten NPC patients were randomly selected to undergo a RapidArc plan with either FFF beams(RA-FFF) or conventional beams(RA-C).The doses to the planning target volumes(PTVs),organs at risk(OARs),and normal tissues were compared.The technical delivery parameters for RapidArc plans were also assessed to compare the characteristics of FFF and conventional beams.Both techniques delivered adequate doses to PTVs.For PTVs,RA-C delivered lower maximum and mean doses and improved conformity and homogeneity compared with RA-FFF.Both techniques provided similar maximum doses to the optic nerves and lenses.For the brain stem,spinal cord,larynx,parotid glands,oral cavity,and skin,RA-FFF showed significant dose increases compared to RA-C.The dose to normal tissue was lower in RA-FFF.The monitor units(MUs) were(536 ± 46) MU for RA-FFF and(501± 25) MU for RA-C.The treatment duration did not significantly differbetween plans.Although both treatment plans could meet clinical needs,RA-C is dosimetrically superior to RA-FFF for NPC radiotherapy.