Dosimetric impact of failing to apply correction factors to ion recombination in percentage depth dose measurements and the volume-averaging effect in flattening filter-free beams

Abstract Purpose: This study aims to evaluate dosimetric parameters like percentage depth dose, dosimetric field size, depth of maximum dose surface dose, penumbra and output factors measured using IBA CC01 pinpoint chamber, IBA stereotactic field diode (SFD), PTW microDiamond against Monte Carlo (MC) simulation for 6 MV flattening filter-free small fields. Materials and Methods: The linear accelerator used in the study was a Varian TrueBeam® STx. All field sizes were defined by jaws. The required shift to effective point of measurement was given for CC01, SFD and microdiamond for depth dose measurements. The output factor of a given field size was taken as the ratio of meter readings normalised to 10 × 10 cm2 reference field size without applying any correction to account for changes in detector response. MC simulation was performed using PRIMO (PENELOPE-based program). The phase space files for MC simulation were adopted from the MyVarian Website. Results and Discussion: Variations were seen between the detectors and MC, especially for fields smaller than 2 × 2 cm2 where the lateral charge particle equilibrium was not satisfied. Diamond detector was seen as most suitable for all measurements above 1 × 1 cm2. SFD was seen very close to MC results except for under-response in output factor measurements. CC01 was observed to be suitable for field sizes above 2 × 2 cm2. Volume averaging effect for penumbra measurements in CC01 was observed. No detector was found suitable for surface dose measurement as surface ionisation was different from surface dose due to the effect of perturbation of fluence. Some discrepancies in measurements and MC values were observed which may suggest effects of source occlusion, shift in focal point or mismatch between real accelerator geometry and simulation geometry. Conclusion: For output factor measurement, TRS483 suggested correction factor needs to be applied to account for the difference in detector response. CC01 can be used for field sizes above 2 × 2 cm2 and microdiamond detector is suitable for above 1 × 1 cm2. Below these field sizes, perturbation corrections and volume averaging corrections need to be applied.

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Planning study and dose measurements of intracranial stereotactic radiation surgery with a flattening filter-free linac

Practical Radiation Oncology ◽

10.1016/j.prro.2013.04.004 ◽

2014 ◽

Vol 4 (2) ◽

pp. e109-e116 ◽

Cited By ~ 7

Author(s):

Yvonne Dzierma ◽

Frank G. Nuesken ◽

Jan Palm ◽

Norbert P. Licht ◽

Christian Ruebe

Keyword(s):

Planning Study ◽

Stereotactic Radiation ◽

Flattening Filter Free ◽

Flattening Filter ◽

Dose Measurements

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Technical Note: Preferred dosimeter size and associated correction factors in commissioning high dose per pulse, flattening filter free x-ray beams

Medical Physics ◽

10.1118/1.4941691 ◽

2016 ◽

Vol 43 (3) ◽

pp. 1507-1513 ◽

Cited By ~ 6

Author(s):

A. Sudhyadhom ◽

N. Kirby ◽

B. Faddegon ◽

C. F. Chuang

Keyword(s):

Technical Note ◽

High Dose ◽

Correction Factors ◽

X Ray ◽

Flattening Filter Free ◽

Flattening Filter

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Open beam dosimetric characteristics of True Beam medical linear accelerator with flattening filter (WFF) and flattening filter free (FFF) beam

Polish Journal of Medical Physics and Engineering ◽

10.2478/pjmpe-2018-0011 ◽

2018 ◽

Vol 24 (2) ◽

pp. 79-89 ◽

Cited By ~ 1

Author(s):

Karthick Raj Mani ◽

Md Anisuzzaman Bhuiyan ◽

Md. Shakilur Rahman ◽

S. M. Azharur Islam

Keyword(s):

Dose Rate ◽

Linear Accelerator ◽

Maximum Dose ◽

Published Data ◽

Depth Dose ◽

Medical Linear Accelerator ◽

Flattening Filter Free ◽

Dosimetric Data ◽

Flattening Filter ◽

Maximum Dose Rate

Abstract True Beam medical linear accelerator is capable of delivering flattening filter free (FFF) and with flattening filter (WFF) photon beams. True Beam linear accelerator is equipped with five photon beam energies (6 FFF, 6 WFF, 10 FFF, 10 WFF and 15 WFF) as well as six electron beam energies (6 MeV, 9 MeV, 12 MeV, 15 MeV and 18 MeV). The maximum dose rate for the 6 WFF, 10 WFF and 15 WFF is 600 MU/min, whereas 6 FFF has a maximum dose rate of 1400 MU/min and 10 FFF with a maximum dose rate of 2400 MU/min. In this report we discussed the open beam dosimetric characteristics of True Beam medical linear accelerator with FFF and WFF beam. All the dosimetric data (i.e. depth dose, cross-line profiles, diagonal profiles, output factors, MLC transmission, etc.) for 6 MV, 6 FFF, 10 MV, 10 FFF and 15 MV were measured and compared with the published data of the True Beam. Multiple detectors were used in order to obtain a consistent dataset. The measured data has a good consistency with the reference golden beam data. The measured beam quality index for all the beams are in good agreement with the published data. The percentage depth dose at 10 cm depth of all the available photon beams was within the tolerance of the Varian acceptance specification. The dosimetric data shows consistent and comparable results with the published data of other True Beam linear accelerators. The dosimetric data provide us an appreciated perception and consistent among the published data and may be used for future references.

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Study of unflattened photon beams shaped by multileaf collimator using BEAMnrc code

Journal of Radiotherapy in Practice ◽

10.1017/s1460396916000340 ◽

2016 ◽

Vol 15 (4) ◽

pp. 392-401

Author(s):

Ankit kajaria ◽

Neeraj Sharma ◽

Shiru Sharma ◽

Satyajit Pradhan ◽

Abhijit Mandal ◽

...

Keyword(s):

Beam Line ◽

Photon Beam ◽

Field Size ◽

Photon Beams ◽

Multileaf Collimators ◽

Depth Dose ◽

Beamnrc Code ◽

Flattening Filter Free ◽

Flattening Filter ◽

Beam Delivery

AbstractPurposeIn our study basic dosimetric properties of a flattening filter free 6 MV photon beam shaped by multileaf collimators (MLC) is examined using the Monte Carlo (MC) method.Methods and MaterialsBEAMnrc code was used to make a MC simulation model for 6 MV photon beam based on Varian Clinic 600 unique performance linac, operated with and without a flattening filter in beam line. Dosimetric features including central axis depth dose, beam profiles, photon and electron spectra were calculated and compared for flattened and unflattened cases.ResultsDosimetric field size and penumbra were found to be smaller for unflattened beam, and the decrease in field size was less for MLC shaped in comparison with jaw-shaped unflattened beam. Increase in dose rate of >2·4 times was observed for unflattened beam indicating a shorter beam delivery time for treatment. MLC leakage was found to decrease significantly when the flattening filter was removed from the beam line. The total scatter factor showed slower deviation with field sizes for unflattened beam indicating a reduced head scatter.ConclusionsOur study demonstrated that improved accelerator characteristics can be achieved by removing flattening filter from beam line.

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Depth Dose Enhancement on Flattening-Filter-Free Photon Beam: A Monte Carlo Study in Nanoparticle-Enhanced Radiotherapy

Applied Sciences ◽

10.3390/app10207052 ◽

2020 ◽

Vol 10 (20) ◽

pp. 7052

Author(s):

James C. L. Chow

Keyword(s):

Monte Carlo ◽

Monte Carlo Study ◽

Photon Beam ◽

Depth Range ◽

Photon Beams ◽

Dose Enhancement ◽

Au Nps ◽

Depth Dose ◽

Flattening Filter Free ◽

Flattening Filter

The aim of this study is to investigate the variations of depth dose enhancement (DDE) on different nanoparticle (NP) variables, when using the flattening-filter-free (FFF) photon beam in nanoparticle-enhanced radiotherapy. Monte Carlo simulation under a macroscopic approach was used to determine the DDE ratio (DDER) with variables of NP material (gold (Au) and iron (III) oxide (Fe2O3)), NP concentration (3–40 mg/mL) and photon beam (10 MV flattening-filter (FF) and 10 MV FFF). It is found that Au NPs had a higher DDER than Fe2O3 NPs, when the depths were shallower than 6 and 8 cm for the 10 MV FF and 10 MV FFF photon beams, respectively. However, in a deeper depth range of 10–20 cm, DDER for the Au NPs was lower than Fe2O3 NPs mainly due to the beam attenuation and photon energy distribution. It is concluded that DDER for the Au NPs and Fe2O3 NPs decreased with an increase of depth in the range of 10–20 cm, with rate of decrease depending on the NP material, NP concentration and the use of FF in the photon beam.

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