Commissioning and dosimetric characteristics of TrueBeam system: Composite data of three TrueBeam machines

The dose measurements of the small field sizes, such as conical collimators used in stereotactic radiosurgery (SRS), are a significant challenge due to many factors including source occlusion, detector size limitation, and lack of lateral electronic equilibrium. One useful tool in dealing with the small field effect is Monte Carlo (MC) simulation. In this study, we report a comparison of Monte Carlo simulations and measurements of output factors for the Varian SRS system with conical collimators for energies of 6 MV flattening filter‐free (6 MV) and 10 MV flattening filter‐free (10 MV) on the TrueBeam accelerator. Monte Carlo simulations of Varian's SRS system for 6 MV and 10 MV photon energies with cones sizes of 17.5 mm, 15.0 mm, 12.5 mm, 10.0 mm, 7.5 mm, 5.0 mm, and 4.0 mm were performed using EGSnrc (release V4 2.4.0) codes. Varian's version‐2 phase‐space files for 6 MV and 10 MV of TrueBeam accelerator were utilized in the Monte Carlo simulations. Two small diode detectors Edge (Sun Nuclear) and Small Field Detector (SFD) (IBA Dosimetry) were applied to measure the output factors. Significant errors may result if detector correction factors are not applied to small field dosimetric measurements. Although it lacked the machine‐specific kQitalicclin,Qitalicmsrfitalicclin,fitalicmsr correction factors for diode detectors in this study, correction factors were applied utilizing published studies conducted under similar conditions. For cone diameters greater than or equal to 12.5 mm, the differences between output factors for the Edge detector, SFD detector, and MC simulations are within 3.0% for both energies. For cone diameters below 12.5 mm, output factors differences exhibit greater variations.PACS number(s): 87.55.k, 87.55.Qr

Section: Introductionmentioning

confidence: 99%

Output factor comparison of Monte Carlo and measurement for Varian TrueBeam 6 MV and 10 MV flattening filter‐free stereotactic radiosurgery system

Cheng

Ning

Arora

et al. 2016

“…On gated treatments, the high dose rate can also be an advantage. Varian's flagship is called True Beam to honor the FFF modes 19 , 20 , 21 , 22 …”

Section: Introductionmentioning

confidence: 99%

On flattening filter‐free portal dosimetry

Pardo

Novais

López

et al. 2016

Varian introduced (in 2010) the option of removing the flattening filter (FF) in their C‐Arm linacs for intensity‐modulated treatments. This mode, called flattening filter‐free (FFF), offers the advantage of a greater dose rate. Varian's “Portal Dosimetry” is an electronic portal imager device (EPID)‐based tool for IMRT verification. This tool lacks the capability of verifying flattening filter‐free (FFF) modes due to saturation and lack of an image prediction algorithm. (Note: the latest versions of this software and EPID correct these issues.) The objective of the present study is to research the feasibility of said verifications (with the older versions of the software and EPID). By placing the EPID at a greater distance, the images can be acquired without saturation, yielding a linearity similar to the flattened mode. For the image prediction, a method was optimized based on the clinically used algorithm (analytical anisotropic algorithm (AAA)) over a homogeneous phantom. The depth inside the phantom and its electronic density were tailored. An application was developed to allow the conversion of a dose plane (in DICOM format) to Varian's custom format for Portal Dosimetry. The proposed method was used for the verification of test and clinical fields for the three qualities used in our institution for IMRT: 6X, 6FFF and 10FFF. The method developed yielded a positive verification (more than 95% of the points pass a 2%/2 mm gamma) for both the clinical and test fields. This method was also capable of “predicting” static and wedged fields. A workflow for the verification of FFF fields was developed. This method relies on the clinical algorithm used for dose calculation and is able to verify the FFF modes, as well as being useful for machine quality assurance. The procedure described does not require new hardware. This method could be used as a verification of Varian's Portal Dose Image Prediction.PACS number(s): 87.53.Kn, 87.55.T‐, 87.56.bd, 87.59.‐e

“…In particular, the bending magnet, carrousel, and electron scattering foils have been redesigned, the primary collimator is thicker than in older units, and an antibackscatter foil has been added 1 , 2 , 3 …”

Section: Introductionmentioning

confidence: 99%

“…Chang et al, (1) Beyer, (2) and Glide‐Hurst et al (3) performed comparisons of select photon and electron fields from unmatched TrueBeam units; in the Beyer and Glide‐Hurst et al studies, the units were installed in different centers. All three studies found their respective machines to be in excellent agreement with one another, Beyer citing percent depth dose (PDD), profile, and output measurements to be reproducible between machines within 2%.…”

Section: Introductionmentioning

confidence: 99%

Comparison of measured Varian Clinac 21EX and TrueBeam accelerator electron field characteristics

Lloyd

Zavgorodni

Gagne

2015

Dosimetric comparisons of radiation fields produced by Varian's newest linear accelerator, the TrueBeam, with those produced by older Varian accelerators are of interest from both practical and research standpoints. While photon fields have been compared in the literature, similar comparisons of electron fields have not yet been reported. In this work, electron fields produced by the TrueBeam are compared with those produced by Varian's Clinac 21EX accelerator. Diode measurements were taken of fields shaped with electron applicators and delivered at 100 cm SSD, as well as those shaped with photon MLCs without applicators and delivered at 70 cm SSD for field sizes ranging from 5×5 to 25×25 cm2 at energies between 6 and 20 MeV. Additionally, EBT2 and EBT3 radio‐chromic film measurements were taken of an MLC‐shaped aperture with closed leaf pairs delivered at 70 cm SSD using 6 and 20 MeV electrons. The 6 MeV fields produced by the TrueBeam and Clinac 21EX were found to be almost indistinguishable. At higher energies, TrueBeam fields shaped by electron applicators were generally flatter and had less photon contamination compared to the Clinac 21EX. Differences in PDDs and profiles fell within 3% and 3 mm for the majority of measurements. The most notable differences for open fields occurred in the profile shoulders for the largest applicator field sizes. In these cases, the TrueBeam and Clinac 21EX data differed by as much as 8%. Our data indicate that an accurate electron beam model of the Clinac 21EX could be used as a starting point to simulate electron fields that are dosimetrically equivalent to those produced by the TrueBeam. Given that the Clinac 21EX shares head geometry with Varian's iX, Trilogy, and Novalis TX accelerators, our findings should also be applicable to these machines.PACS number: 87.56.bd