The impact of flattening-filter-free beam technology on 3D conformal RT

Abstract

BackgroundThe removal of the flattening filter (FF) leads to non-uniform fluence distribution with a considerable increase in dose rate. It is possible to adapt FFF beams (flattening-filter-free) in 3D conformal radiation therapy (3D CRT) by using field in field techniques (FiF). The aim of this retrospective study is to clarify whether the quality of 3D CRT plans is influenced by the use of FFF beams.MethodThis study includes a total of 52 CT studies of RT locations that occur frequently in clinical practice. Dose volume targets were provided for the PTV of breast (n=13), neurocranium (n=11), lung (n=7), bone metastasis (n=10) and prostate (n=11) in line with ICRU report 50/62. 3D CRT planning was carried out using FiF methods. Two clinically utilized photon energies are used for a Siemens ARTISTE linear accelerator in FFF mode at 7MVFFF and 11MVFFF as well as in FF mode at 6MVFF and 10MVFF. The plan quality in relation to the PTV coverage, OAR (organs at risk) and low dose burden as well as the 2D dosimetric verification is compared with FF plans.ResultsNo significant differences were found between FFF and FF plans in the mean dose for the PTV of breast, lung, spine metastasis and prostate. The low dose parameters V5Gy and V10Gy display significant differences for FFF and FF plans in some subgroups. The DVH analysis of the OAR revealed some significant differences. Significantly more fields (1.9 – 4.5) were necessary in the use of FFF beams for each location (p<0.0001) in order to achieve PTV coverage. All the tested groups displayed significant increases (1.3 – 2.2 times) in the average number of necessary MU with the use of FFF beams (p<0.001).ConclusionsThis study has shown that the exclusive use of a linear accelerator in FFF mode is feasible in 3D CRT. It was possible to realize RT plans in comparable quality in typical cases of clinical radiotherapy. The 2D dosimetric validation of the modulated fields verified the dose calculation and thus the correct reproduction of the characteristic FFF parameters in the planning system that was used.

Evaluation of the dosimetric impact of applying flattening filter‐free beams in intensity‐modulated radiotherapy for early‐stage upper thoracic carcinoma of oesophagus

“…However, removal of the flattening filter has greatly increased the dose output by two to threefold and the time required to deliver the total MU was reduced, which had outweighed the time needed by the increased MU. This was in line with the several previous studies in which reduction of TT of 20–50% have been reported 17,20,21. Because of this advantage, the use of FFF beams has been extended to VMAT treatment of nasopharynx22 and prostate23 cancers.…”

“…This was in line with the several previous studies in which reduction of TT of 20-50% have been reported. 17,20,21 Because of this advantage, the use of FFF beams has been extended to VMAT treatment of nasopharynx 22 and prostate 23 cancers. Nevertheless, despite the FFF beam technology demonstrated attractive practical advantages over the conventional beam IMRT, the understanding of the biological effect of such a high dose rate treatment on body tissues which may have consequence on late toxicities is still not certain and needs to be proven by longer term clinical studies.…”

Comparative Planning of Flattening-Filter-Free and Flat Beam IMRT for Hypopharynx Cancer as a Function of Beam and Segment Number

“…Third, flattening-filter-free (FFF) beams can be applied in both IMRT and VMAT treatment planning, with the practical advantage of much higher dose rates as compared with normal flat beams [6]. A draw-back to be considered here is that the conical beam profile of FFF beams is generally found to require more segments and/or more monitor units to achieve the same standards of PTV homogeneity than for flat beams (e.g., [7]–[8]); this again lengthens treatment time somewhat, particularly for large PTVs. The greatest reduction in treatment time may arise from a combination of arc treatment with FFF beams; however, here we will consider FFF beams in IMRT treatment planning because of its rapidly spreading availability.…”

Use of Flattening Filter Free Photon Beams for Off-axis Targets in Conformal Arc Stereotactic Body Radiation Therapy

“…1,2) Flatteningfilter-free (FFF) beams can increase delivery efficiency by employing a high-dose rate that greatly reduces the beam on time (BOT). [3][4][5][6][7][8] This makes them useful for treatments requiring a high dose per fraction, such as SBRT. The increased efficiency of FFF beams can also aid in respiratory motion management, including the use of voluntary breath hold techniques, by enabling entire beam delivery within a short number of breath holds.…”