Delivery time comparison for intensity-modulated radiation therapy with/without flattening filter: a planning study

Abstract

The treatment delivery time of intensity-modulated radiation therapy (IMRT) with a multileaf collimator (MLC) is generally longer than that of conventional radiotherapy. In theory, removing the flattening filter from the treatment head may reduce the beam-on time by enhancing the output dose rate, and then reduce the treatment delivery time. And in practice, there is a possibility of delivering the required fluence distribution by modulating the unflattened non-uniform fluence distribution. However, the reduction of beam-on time may be discounted by the increase of leaf-travel time and (or) verification-and-recording (V&R) time. Here we investigate the overall effect of flattening filter on the treatment delivery time of IMRT with MLCs implemented in the step and shoot method, as well as with compensators on six hybrid machines. We compared the treatment delivery time with/without flattening filter for ten nasopharynx cases and ten prostate cases by observing the variations of the ratio of the beam-on time, segment number, leaf-travel time and the treatment delivery time with dose rate, leaf speed and V&R time. The results show that, without the flattening filter, the beam-on time reduces for both static MLC and compensator-based techniques: the number of segments and the leaf-travel time increase slightly for the static MLC technique; the relative IMRT treatment delivery time decreases more with lower dose rate, higher leaf speed and shorter V&R overhead time. The absolute treatment delivery time reduction depends on the fraction dose. It is not clinically significant at a fraction dose of 2 Gy for the technique of removing the flattening filter, but becomes significant when the fraction dose is as high as that for radiosurgery.

Multisource modeling of flattening filter free (FFF) beam and the optimization of model parameters

“…Cashmore 9 also reported similar results of dosimetric properties for a 6 MV FFF beam using an Elekta Precise linear accelerator. Vassiliev [5][6][7][8]10,11 In addition, some of them suggested novel methods of beam source modeling that could be used to improve the speed of MC-based dose calculation. 8,10 However, these methods are computationally intensive and it is difficult to apply them in clinical treatment planning.…”

Monte Carlo study on a flattening filter-free 18-MV photon beam of a medical linear accelerator

“…Some recent research studies have shown that removing FF from the linac head can increase the dose rate considerably, and it may have applications with IMRT and other multi-leaf collimator (MLC)-based modalities. 4,5 A study on IMRT with the FF free photon beam revealed that its dose distribution properties are comparable with those of the standard beam, and the amount of out-of-fi eld dose was decreased using FF free beams. 5 Monte Carlo (MC) method is a powerful tool for analyzing linac head components and infl uencing factors on beam characteristics.…”

“…4,5 A study on IMRT with the FF free photon beam revealed that its dose distribution properties are comparable with those of the standard beam, and the amount of out-of-fi eld dose was decreased using FF free beams. 5 Monte Carlo (MC) method is a powerful tool for analyzing linac head components and infl uencing factors on beam characteristics. 6,7 Thus, the effect of FF on photon energy spectra, depth doses, and beam profi les could be studied by an MC method.…”

A surface energy spectral study on the bone heterogeneity and beam obliquity using the flattened and unflattened photon beams

“…[1][2][3][4][5] With the removal of the flattening filter which generates a uniform beam profile for 3D-conformal radiotherapy, the output of the photon beam is highly increased. 6,7 For example, the Varian TrueBEAM linear accelerator can produce 1400 monitor units (MU) and 2400 MU per minute for the 6 and 10 MV photon beams, respectively. This dose rate from the flattening-filter free linear accelerator is about 2-3 times higher than the conventional accelerator producing flattened photon beams, and can shorten the treatment time.…”