skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: SU-F-T-467: A Cross-Checking Approach for Dosimetric Verification of Beam- Matched Elekta Linear Accelerators

Abstract

Purpose: To verify the similarity of the dosimetric characteristics between two Elekta linear accelerators (linacs) in order to treat patients interchangeably on these two machines without re-planning. Methods: To investigate the viability of matching the 6 MV flattened beam on an existing linac (Elekta Synergy with Agility head) with a recently installed new linca (Elekta Versa HD), percent depth doses (PDD), flatness and symmetry output factors were compared for both machines. To validate the beam matching among machines, we carried out two approaches to cross-check the dosimetrical equivalence: 1) the prior treatment plans were re-computed based on the newly built Versa HD treatment planning system (TPS) model without changing the beam control points; 2) The same plans were delivered on both machines and the radiation dose measurements on a MapCheck2 were compared with TPS calculations. Three VMAT plans (Head and neck, lung, and prostate) were used in the study. Results: The difference between the PDDs for 10×10 cm{sup 2} field at all depths was less than 0.8%. The difference of flatness and symmetry for 30×30 cm{sup 2} field was less than 0.8%, and the measured output factors varies by less than 1% for each field size ranging from 2×2 cm2more » to 40×40 cm{sup 2}. For the same plans, the maximum difference of the two calculated dose distributions is 2% of prescription. For the QA measurements, the gamma index passing rates were above 99% for 3%/3mm criteria with 10% threshold for all three clinical plans. Conclusion: A beam modality matching between two Elekta linacs is demonstrated with a cross-checking approach.« less

Authors:
; ; ; ; ; ;  [1]
  1. University Hospitals Case Medical Center, Dept of Radiation Oncology, Cleveland, OH (United States)
Publication Date:
OSTI Identifier:
22649057
Resource Type:
Journal Article
Resource Relation:
Journal Name: Medical Physics; Journal Volume: 43; Journal Issue: 6; Other Information: (c) 2016 American Association of Physicists in Medicine; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
60 APPLIED LIFE SCIENCES; 61 RADIATION PROTECTION AND DOSIMETRY; 43 PARTICLE ACCELERATORS; BEAMS; DEPTH DOSE DISTRIBUTIONS; HEAD; LINEAR ACCELERATORS; PLANNING; RADIATION DOSES

Citation Formats

Zheng, Y, Yuan, J, Geis, P, Colussi, V, Machtay, M, Ellis, R, and Wessels, B. SU-F-T-467: A Cross-Checking Approach for Dosimetric Verification of Beam- Matched Elekta Linear Accelerators. United States: N. p., 2016. Web. doi:10.1118/1.4956652.
Zheng, Y, Yuan, J, Geis, P, Colussi, V, Machtay, M, Ellis, R, & Wessels, B. SU-F-T-467: A Cross-Checking Approach for Dosimetric Verification of Beam- Matched Elekta Linear Accelerators. United States. doi:10.1118/1.4956652.
Zheng, Y, Yuan, J, Geis, P, Colussi, V, Machtay, M, Ellis, R, and Wessels, B. 2016. "SU-F-T-467: A Cross-Checking Approach for Dosimetric Verification of Beam- Matched Elekta Linear Accelerators". United States. doi:10.1118/1.4956652.
@article{osti_22649057,
title = {SU-F-T-467: A Cross-Checking Approach for Dosimetric Verification of Beam- Matched Elekta Linear Accelerators},
author = {Zheng, Y and Yuan, J and Geis, P and Colussi, V and Machtay, M and Ellis, R and Wessels, B},
abstractNote = {Purpose: To verify the similarity of the dosimetric characteristics between two Elekta linear accelerators (linacs) in order to treat patients interchangeably on these two machines without re-planning. Methods: To investigate the viability of matching the 6 MV flattened beam on an existing linac (Elekta Synergy with Agility head) with a recently installed new linca (Elekta Versa HD), percent depth doses (PDD), flatness and symmetry output factors were compared for both machines. To validate the beam matching among machines, we carried out two approaches to cross-check the dosimetrical equivalence: 1) the prior treatment plans were re-computed based on the newly built Versa HD treatment planning system (TPS) model without changing the beam control points; 2) The same plans were delivered on both machines and the radiation dose measurements on a MapCheck2 were compared with TPS calculations. Three VMAT plans (Head and neck, lung, and prostate) were used in the study. Results: The difference between the PDDs for 10×10 cm{sup 2} field at all depths was less than 0.8%. The difference of flatness and symmetry for 30×30 cm{sup 2} field was less than 0.8%, and the measured output factors varies by less than 1% for each field size ranging from 2×2 cm2 to 40×40 cm{sup 2}. For the same plans, the maximum difference of the two calculated dose distributions is 2% of prescription. For the QA measurements, the gamma index passing rates were above 99% for 3%/3mm criteria with 10% threshold for all three clinical plans. Conclusion: A beam modality matching between two Elekta linacs is demonstrated with a cross-checking approach.},
doi = {10.1118/1.4956652},
journal = {Medical Physics},
number = 6,
volume = 43,
place = {United States},
year = 2016,
month = 6
}
  • Purpose: The increasing application of VMAT demands a more efficient workflow and QA solution. This study aims to investigate the feasibility of performing VMAT QA measurements on one linac for plans treated on other beam-matched Elekta Agility linacs. Methods: A single model was used to create 24 clinically approved VMAT plans (12 head-and-neck and 12 prostate using 6MV and 10MV respectively) on Pinnacle v9.10 (Philips, Einhoven, Netherlands). All head-and-neck plans were delivered on three beam-matched machines while all prostate cases were delivered on two beam-matched 10MV Agility machines. All plans were delivered onto PTW Octavius 4D phantom with 1500 detectormore » array (PTW, Freiburg, Germany). Reconstructed volume doses were then compared with the Pinnacle reference plans in Verisoft 6.1 under 3%/3mm gamma criteria at local dose. Plans were considered clinically acceptable if >90% of the voxels passing the gamma criteria. Results: All measurements were passed (3D gamma passing rate >90%) and the result shows that the mean difference of 3D gamma of 12 head-and-neck cases is 1.2% with standard deviation of 0.6%. While for prostate cases, the mean difference of 3D gamma is 0.9% with standard deviation of 0.7%. Maximum difference of 3D gamma of all measurements between beam-matched machines is less than 2.5%. The differences of passing rates between different machines were statistically insignificant (p>0.05). Conclusion. The result suggests that ther Conclusion: The result suggests that there exists a 3D gamma threshold, in our case 92.5%, above which the VMAT QA performed in any one of beam-matched machine will also pass in another one. Therefore, VMAT QA efficiency may be increased and phantom set up time can be saved by implementing such method. A constant performance across all beam matched machines must be maintained to make this QA approach feasible.« less
  • The purpose of this study is to analyze the dosimetric effect of Elekta Beam Modulator in 3-dimensional conformal radiation therapy (3DCRT) and in intensity-modulated radiation therapy (IMRT) for localized prostate cancer. We compared treatment plans developed with 2 different Elekta multileaf collimators (MLC): Beam Modulator micro-MLC (mMLC) (4-mm leaf width at the isocenter) and standard MLC (10-mm leaf width at the isocenter). The comparison was performed for 15 patients with localized prostate cancer in 3DCRT and IMRT delivery; a total of 60 treatment plans were processed. The dose-volume histograms were used to provide the quantitative comparison between plans. In particular,more » we analyzed differences between rectum and bladder sparing in terms of a set of appropriate Vx (percentage of organ at risk [OAR] volume receiving the x dose) and differences between target conformity and coverage in terms of coverage factor and conformation number. Our analysis demonstrates that in 3DCRT there is an advantage in the use of Elekta Beam Modulator mMLC in terms of organ sparing; in particular, a significant decrease in rectal V{sub 60} and V{sub 50} (p = 0.001) and in bladder V{sub 70} and V{sub 65} (p = 0.007 and 0.002, respectively) was found. Moreover, a better target dose conformity was obtained (p = 0.002). IMRT plans comparison demonstrated no significant differences between the use of the 4 or 10-mm MLCs. Our analysis shows that in 3DCRT the use of the Elekta Beam Modulator mMLC gives a gain in target conformity and in OARs dose sparing whereas in IMRT plans there is no advantage.« less
  • Purpose The purpose of this work is to publish beam data from Elekta Synergy(R) linear accelerators with Agility(TM) MLC for total skin electron beam (TSEB) therapy using the HDRE1 (High Dose Rate Electron 6MeV) energy. Method & Materials The optimal gantry angles for TSEB were determined using ion chamber measurements along a vertical profile at 450cm SSD. After gantry angles were chosen, field uniformity was measured over the entire treatment area. Uniformity was measured with and without the patient support device, allowing the dosimetric effect of the support device to be determined. Beam output and PDD were measured at themore » calibration point (450cm SSD) for a dual beam using a parallel plate chamber in solid water. These measurements were repeated with the chamber and phantom rotated about the patient isocenter at various angles, in order to measure the contribution from oblique beams. This technique provides a precise measurement of the treatment skin dose (TSD). Lastly, ion chamber measurements were verified by film and diodes. Results The optimal gantry angle for 450 cm SSD was determined to be 90±16°. This achieved uniformity better than 96% on the vertical axis, and 92% along the horizontal axis. HDRE1 was calibrated to deliver 10 cGy/MU at standard geometry (100 cm SSD, 1.2 cm depth). Thus at TSEB geometry (450 cm SSD, 0.1 cm depth) the output of the AP dual field was measured to be 0.35 cGy/MU. The TSD of a 20 cm radius cylinder for six (equally, 60° spaced) dual fields was measured to be 1.19 cGy/MU. Percent Depth Dose data for the AP dual field and TSD are shown in Figure 2. Conclusion This paper provides a modern procedure for commissioning TSEB therapy on a linear accelerator, and clinical beam data for the Elekta Synergy(R) with Agility(TM) MLC.« less
  • Purpose: Accurately determining out-of-field doses when using electron beam radiotherapy is of importance when treating pregnant patients or patients with implanted electronic devices. Scattered doses outside of the applicator field in electron beams have not been broadly investigated, especially since manufacturers have taken different approaches in applicator designs. Methods: In this study, doses outside of the applicator field were measured for electron beams produced by a 10×10 applicator on two Varian 21iXs operating at 6, 9, 12, 16, and 20 MeV, a Varian TrueBeam operating at 6, 9, 12, 16, and 20 MeV, and an Elekta Versa HD operating atmore » 6, 9, 12 and 15 MeV. Peripheral dose profiles and percent depth doses were measured in a Wellhofer water phantom at 100 cm SSD with a Farmer ion chamber. Doses were compared to peripheral photon doses from AAPM’s Task Group #36 report. Results: Doses were highest for the highest electron energies. Doses typically decreased with increasing distance from the field edge but showed substantial increases over some distance ranges. Substantial dose differences were observed between different accelerators; the Elekta accelerator had much higher doses than any Varian unit examined. Surprisingly, doses were often similar to, and could be much higher than, doses from photon therapy. Doses decreased sharply with depth before becoming nearly constant; the dose was found to decrease to a depth of approximately E(MeV)/4 in cm. Conclusion: The results of this study indicate that proper shielding may be very important when utilizing electron beams, particularly on a Versa HD, while treating pregnant patients or those with implanted electronic devices. Applying a water equivalent bolus of Emax(MeV)/4 thickness (cm) on the patient would reduce fetal dose drastically for all clinical energies and is a practical solution to manage the potentially high peripheral doses seen from modern electron beams. Funding from NIH Grant number: #CA180803.« less
  • Purpose: Log file based IMRT and VMAT QA is a system that analyzes treatment log files and uses delivery parameters to compute the dose to the patient/phantom. This system was previously commissioned for Varian machines, the purpose of this work is to describe the process for commissioning Mobius for use with Elekta machines. Methods: Twelve IMRT and VMAT plans (6×) were planned and delivered and dose was measured using MapCheck, the results were compared to that computed by Mobius. For 10x and 18x, plans were generated, copied to a phantom and delivered, the dose was measured using a single ionmore » chamber. The difference in measured dose to computed dose (Mobius) was used to adjust the dynamic leaf gap (DLG) in Mobius to achieve optimal agreement between measurements, Mobius and treatment plans. Results: For the measured dose comparison, the average 3%/3mm gamma 97.1% of pixels passed criteria using MapCheck where Mobius computed 96.9% of voxels passing. For 10×, a DLG of −5.5 was determined to achieve optimal results for TPS and measured ion chamber data with an average 0.1% difference and −1.7% respectively. For 18×, a DLG of −3 was determined to achieve optimal results from the TPS and measured data with an average of −0.7% and −1.4% difference on average from a set of IMRT and VMAT plans. The 6x data needed no DLG correction to arrive at agreement with the TPS and the MapCheck measured data. Conclusion: We have validated with measurements for IMRT and VMAT cases the use of Mobius FX with Elekta treatment machines for IMRT and VMAT QA. For 6×, no adjustments to the DLG were required to obtain good results utilizing Mobius whereas for 10× and 18×, the DLG had to be adjusted to obtain optimum agreement with measured data and our TPS.« less