Characteristics of flattening filter free beams at low monitor unit settings

Akino, Yuichi; Ōta, Shōzō; Inoue, Shinichi; Mizuno, Hirokazu; Sumida, Iori; Yoshioka, Yasuo; Isohashi, Fumiaki; Ogawa, Kazuhiko

doi:10.1118/1.4824920

Cited by 10 publications

(9 citation statements)

References 39 publications

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“…The maximum nominal dose rate is 500 MU/min in FF Mode and 1700 MU/min in FFF mode. Beam profiles, depth doses and dose output were found to be stable for 4 MU and larger in both irradiation modes as also reported by Akino [ 14 ]. Verification of the linac model in Oncentra by collapsed cone dose calculations of percentage depth doses, profiles and output factors was within specifications of Oncentra®, i.e.…”

Section: Methodssupporting

confidence: 83%

“…The latest development in the technology of linear accelerators is therefore the opportunity to irradiate patients without a flattening filter in the beam path to increase dose rate and reduce beam-on times as well as out-of-field doses [ 1 ]. The physical properties of flattening filter free beams have been subject to a wide number of investigations during the last years [ 4 – 14 ]. Several treatment planning studies have been published to assess the clinical value of FFF beams for patient treatment, most of them using Varian linear accelerators [ 15 – 23 ].…”

Section: Introductionmentioning

confidence: 99%

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Re-irradiating spinal column metastases using IMRT and VMAT with and without flattening filter - a treatment planning study

et al. 2016

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BackgroundThe aim of this study was to investigate the potential of the flattening filter free (FFF) mode of a linear accelerator for intensity modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT) for patients with in-field recurrence of vertebral metastases.MethodsAn Elekta Synergy Linac with Agility™ head is used to simulate the treatment of ten patients with locally recurrent spinal column metastases. Four plans were generated for each patient treating the vertebrae sparing the spinal cord: Dual arc VMAT and nine field step and shoot IMRT each with and without flattening filter. Plan quality was assessed considering target coverage and sparing of the spinal cord and normal tissue. All plans were verified by a 2D-ionisation-chamber-array, peripheral doses were measured and compared to calculations. Delivery times were measured and compared. The Wilcoxon test was used for statistical analysis with a significance level of 0.05.ResultsTarget coverage, homogeneity index and conformity index were comparable for both flat and flattening filter free beams. The volume of the spinal cord receiving the allowed maximum dose to keep the risk of radiation myelopathy at 0 % was at the same time significantly reduced to below the clinically relevant 1 ccm using FFF mode. In addition the mean dose deposited in the surrounding healthy tissue was significantly reduced in the FFF mode. All four techniques showed equally good gamma scores for plan verification. FFF plans required considerably more MU per fraction dose. Regardless of the large number of MU, out-of-field point dose was significantly lower for FFF plans, with an average reduction of 33 % and mean delivery time was significantly reduced by 22 % using FFF beams. When compared to IMRT FF, VMAT FFF offered even a reduction of 71 % in delivery time and 45 % in peripheral dose.ConclusionsFFF plans showed a significant improvement in sparing of normal tissue and the spinal cord, keeping target coverage and homogeneity comparable. In addition, delivery times were significantly reduced for FFF treatments, minimizing intrafractional motion as well as strain for the patient. Shortest delivery times were achieved using VMAT FFF. For radiotherapy of spinal column metastases VMAT FFF may therefore be considered the preferable treatment option for the combination of Elekta Synergy Linacs and Oncentra® External Beam v4.5 treatment planning system.

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Section: Methodssupporting

confidence: 83%

Section: Introductionmentioning

confidence: 99%

Re-irradiating spinal column metastases using IMRT and VMAT with and without flattening filter - a treatment planning study

et al. 2016

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“…Due to limitations in the speed of mechanical movements, the maximum dose rate is, however, not applied throughout VMAT treatments. Beam profiles, depth doses and dose output were found to be stable for 4 MU and larger in both irradiation modes as also reported by Akino [24]. Verification of the linac model in Monaco 5.0 with XVMC dose calculations of absolute dose, percentage depth doses, profiles, and output factors was within specifications for both FF and FFF.…”

Section: Methodssupporting

confidence: 82%

Simultaneous integrated boost (SIB) radiation therapy of right sided breast cancer with and without flattening filter - A treatment planning study

et al. 2016

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BackgroundThe aim of the study was to compare the two irradiation modes with (FF) and without flattening filter (FFF) for three different treatment techniques for simultaneous integrated boost radiation therapy of patients with right sided breast cancer.MethodsAn Elekta Synergy linac with Agility collimating device is used to simulate the treatment of 10 patients. Six plans were generated in Monaco 5.0 for each patient treating the whole breast and a simultaneous integrated boost (SIB) volume: intensity modulated radiation therapy (IMRT), volumetric modulated arc therapy (VMAT) and a tangential arc VMAT (tVMAT), each with and without flattening filter. Plan quality was assessed considering target coverage, sparing of the contralateral breast, the lungs, the heart and the normal tissue. All plans were verified by a 2D-ionisation-chamber-array and delivery times were measured and compared. The Wilcoxon test was used for statistical analysis with a significance level of 0.05.ResultsSignificantly best target coverage and homogeneity was achieved using VMAT FFF with V95% = (98.7 ± 0.8) % and HI = (8.2 ± 0.9) % for the SIB and V95% = (98.3 ± 0.7) % for the PTV, whereas tVMAT showed significantly lowest doses to the contralateral organs at risk with a Dmean of (0.7 ± 0.1) Gy for the contralateral lung, (1.0 ± 0.2) Gy for the contralateral breast and (1.4 ± 0.2) Gy for the heart. All plans passed the gamma evaluation with a mean passing rate of (99.2 ± 0.8) %. Delivery times were significantly reduced for VMAT and tVMAT but increased for IMRT, when FFF was used. Lowest delivery times were observed for tVMAT FFF with (1:20 ± 0:07) min.ConclusionBalancing target coverage, OAR sparing and delivery time, VMAT FFF and tVMAT FFF are considered the preferable of the investigated treatment options in simultaneous integrated boost irradiation of right sided breast cancer for the combination of an Elekta Synergy linac with Agility and the treatment planning system Monaco 5.0.

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“…It has been shown in many studies that the characteristics of FFF beams differ from those of flattened beams in terms of the cone‐shaped OCR, lower effective beam energy affecting the percent depth dose (PDD), photon energy spectrum affecting the water–air stopping power ratio, and high dose per pulse affecting the ion recombination coefficient . Moreover, the type of the detector may affect the collected beam data.…”

Section: Introductionmentioning

confidence: 99%

Impact of detector selections on inter‐institutional variability of flattening filter‐free beam data for TrueBeam™ linear accelerators

Tanaka

Akino

Mizuno

et al. 2019

J Applied Clin Med Phys

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This study evaluates the type of detector influencing the inter-institutional variability in flattening filter-free (FFF) beam-specific parameters for TrueBeam™ linear accelerators (Varian Medical Systems,Palo Alto, CA, USA). Twenty-four beam data sets, including the percent depth dose (PDD), off-center ratio (OCR), and output factor (OPF) for modeling within the Eclipse (Varian Medical Systems) treatment planning system, were collected from 19 institutions. Although many institutions collected the data using CC13 (IBA Dosimetry, Schwarzenbruck, Germany) or PTW31010 semiflex (PTW Freiburg, Freiburg, Germany) ionization chambers, some institutions used diode detectors, diamond detectors, and ionization chambers with smaller cavities. The OCR data included penumbra width, full width at half maximum (FWHM), and FFF beam-specific parameters, including unflatness and slope. The data measured by CC13/PTW31010 ionization chambers were compared with those measured by all other detectors. PDD data demonstrated the variations within ±1% at the dose fall-off region deeper than peak depth. The penumbra widths of the OCR measured with the CC13/PTW31010 detectors were significantly larger than those measured with all other detectors (P < 0.05). Especially the EDGE detector (Sun Nuclear Corp., Melbourne, FL, USA) and the microDiamond detectors (model 60019; PTW Freiburg) demonstrated much smaller penumbra values compared to those of the CC13/PTW31010 detectors for the 30 × 30 mm 2 field. There was no difference in the FWHM, unflatness, and slope parameters between the values for the CC13/ PTW31010 detectors and all other detectors. OPF curves demonstrated small variations, and the relative difference from the mean value of each data point was almost within 1% for all field sizes. Although the penumbra region exhibited detector-dependent variations, all other parameters showed tiny interunit variations regardless of the detector type. P A C S 87.56.bd K E Y W O R D S beam data commissioning, detector selection, flattening filter-free beam, TrueBeam

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Characteristics of flattening filter free beams at low monitor unit settings

Cited by 10 publications

References 39 publications

Re-irradiating spinal column metastases using IMRT and VMAT with and without flattening filter - a treatment planning study

Re-irradiating spinal column metastases using IMRT and VMAT with and without flattening filter - a treatment planning study

Simultaneous integrated boost (SIB) radiation therapy of right sided breast cancer with and without flattening filter - A treatment planning study

Impact of detector selections on inter‐institutional variability of flattening filter‐free beam data for TrueBeam™ linear accelerators

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