[P278] The use of flattening filter free irradiation mode in normo-fractionated treatments

Purpose The aim of this study was to identify general advantages and disadvantages of the flattening filter free irradiation mode in normo-fractionated intensity modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT). Methods Various studies have been performed at our department to identify specific advantages and disadvantages of the use of the flattening filter free irradiation mode for the normo-fractionated treatment of different tumor sites. Volumetric modulated arc therapy (VMAT) and intensity modulated radiation therapy (IMRT) plans were created with and without flattening filter for at least 10 patients for each tumor site. All treatment plans were verified by a 2D-ionization-chamber-array and delivery times were measured from first beam on to last beam off. Peripheral doses were determined with an ionization chamber as a measure of radiation induced second cancer risk. Differences were evaluated in terms of plan quality, irradiation time, and radiation induced second cancer risk. The results of these studies were reviewed to assess general advantages or disadvantages independent on the specific tumor entity or treatment technique. Results Differences in plan quality and irradiation time were dependent on the tumor entity and treatment technique. The peripheral dose as a measure of radiation induced second cancer risk, however, was significantly reduced in the flattening filter free mode for all tumor sites and treatment techniques. The reduction ranged from 17% to 33%. Conclusion The only general advantage of the flattening filter free irradiation mode observed for all tumor sites and treatment techniques was a reduction in dose to peripheral organs corresponding to a reduction in radiation induced second cancer risk in these organs. No general advantage or disadvantage could be observed in terms of plan quality or treatment time