Evaluation of the dosimetric characteristics of 6 MV flattened and unflattened photon beam

Mohammed, Maged; Chakir, E.; Boukhal, H.; Mroan, S.; Bardouni, T. El

doi:10.1016/j.jksus.2016.09.008

Cited by 13 publications

(14 citation statements)

References 21 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…6 Also, Monte Carlo (MC) studies have shown that the fluence of contamination electrons is greater in FFF beams, which contributes further to the rise in superficial dose. 7,8 Published studies have demonstrated an increase in mean energy at the surface and superficial dose for standard C-arm linacs in FFF mode in both MC simulations 7,8 and commissioning beam data. 5,9 Another important consequence of the Halcyon design that may affect superficial dose is the presence of the bore cover in the beam path, which may act like a beam spoiler increasing the superficial dose to the patient.…”

Section: Introductionmentioning

confidence: 99%

Increase in Superficial Dose in Whole-Breast Irradiation With Halcyon Straight-Through Linac Compared With Traditional C-arm Linac With Flattening Filter: In vivo Dosimetry and Planning Study

O’grady

Barsky

Anamalayil

et al. 2020

Advances in Radiation Oncology

View full text Add to dashboard Cite

Superficial dose is an important parameter in breast cancer radiation therapy. When treated with conventional linacs, bolus is commonly applied to improve target coverage near the surface while also managing the risk of severe skin reactions and negative cosmesis. With the introduction of modern linacs with 6X flattening filter free (FFF) photon beams, the effect on superficial dose and the need for bolus must be evaluated. Methods and Materials:In vivo measurements of superficial dose were made with optically stimulated luminescence dosimeters on 11 breast cancer patients treated with the Halcyon 6X FFF linac (Varian Medical Systems, Palo Alto, CA). Additionally, measurements were made with the Halycon 6X FFF beam and a 6X beam with flattening filter (FF) delivered to an anthropomorphic phantom. A planning study was carried out in which 14 patients treated on the Halcyon were replanned with a conventional linac to determine the difference in superficial dose predicted by the treatment planning system. Measures were taken to increase the accuracy of the treatment planning system superficial dose.

show abstract

Section: Introductionmentioning

confidence: 99%

Increase in Superficial Dose in Whole-Breast Irradiation With Halcyon Straight-Through Linac Compared With Traditional C-arm Linac With Flattening Filter: In vivo Dosimetry and Planning Study

O’grady

Barsky

Anamalayil

et al. 2020

Advances in Radiation Oncology

View full text Add to dashboard Cite

show abstract

“…In addition, the flatness of each depth was approximately 9–13%, which was high owing to the flattening filter‐free (FFF) beam characteristics. The penumbra was not sufficiently steep in this case compared to the existing commercial equipment owing to differences in the focal spot size, jaw, and MLC tip shape, which will be compensated for by improving this aspect in future work 34 …”

Section: Resultsmentioning

confidence: 99%

Medical X‐band linear accelerator for high‐precision radiotherapy

et al. 2021

View full text Add to dashboard Cite

Purpose Recently, high‐precision radiotherapy systems have been developed by integrating computerized tomography or magnetic resonance imaging to enhance the precision of radiotherapy. For integration with additional imaging systems in a limited space, miniaturization and weight reduction of the linear accelerator (linac) system have become important. The aim of this work is to develop a compact medical linac based on 9.3 GHz X‐band RF technology instead of the S‐band RF technology typically used in the radiotherapy field. Methods The accelerating tube was designed by 3D finite‐difference time‐domain and particle‐in‐cell simulations because the frequency variation resulting from the structural parameters and processing errors is relatively sensitive to the operating performance of the X‐band linac. Through the 3D simulation of the electric field distribution and beam dynamics process, we designed an accelerating tube to efficiently accelerate the electron beam and used a magnetron as the RF source to miniaturize the entire linac. In addition, a side‐coupled structure was adopted to design a compact linac to reduce the RF power loss. To verify the performance of the linac, we developed a beam diagnostic system to analyze the electron beam characteristics and a quality assurance (QA) experimental environment including 3D lateral water phantoms to analyze the primary performance parameters (energy, dose rate, flatness, symmetry, and penumbra) The QA process was based on the standard protocols AAPM TG‐51, 106, 142 and IAEA TRS‐398. Results The X‐band linac has high shunt impedance and electric field strength. Therefore, even though the length of the accelerating tube is 37 cm, the linac could accelerate an electron beam to more than 6 MeV and produce a beam current of more than 90 mA. The transmission ratio is measured to be approximately 30% ~ 40% when the electron gun operates in the constant emission region. The percent depth dose ratio at the measured depths of 10 and 20 cm was approximately 0.572, so we verified that the photon beam energy was matched to approximately 6 MV. The maximum dose rate was measured as 820 cGy/min when the source‐to‐skin distance was 80 cm. The symmetry was smaller than the QA standard and the flatness had a higher than standard value due to the flattening filter‐free beam characteristics. In the case of the penumbra, it was not sufficiently steep compared to commercial equipment, but it could be compensated by improving additional devices such as multileaf collimator and jaw. Conclusions A 9.3 GHz X‐band medical linac was developed for high‐precision radiotherapy. Since a more precise design and machining process are required for X‐band RF technology, this linac was developed by performing a 3D simulation and ultraprecision machining. The X‐band linac has a short length and a compact volume, but it can generate a validated therapeutic beam. Therefore, it has more flexibility to be coupled with imaging systems such as CT or MRI and can reduce the bore size of the gantry. In add...

show abstract

“…Our obtained relative surface dose of the flat 6 MV beam line tended to decrease by about 21% (22%) for 10×10 cm 2 (20×20 cm 2 ) field size when the flattening filter was removed from the beam line. Contrarily, the Mohammed et al [41] showed an increase in relative surface dose by about 19% (12%) for 10×10 cm 2 (20×20 cm 2 ) field size by removing the flattening filter from a Varian 2100 linac. For the Siemens FFF, our results converge with the results of Sigamani and Nambiray [3] who evaluated the buildup region and surface dose the Siemens Artiste 7MV-FFF and 6MV flattened photon beams using GafChromic film and two different dosimeters.…”

Section: Discussionmentioning

confidence: 99%

Monte-Carlo simulation of the Siemens Artiste linear accelerator flat 6 MV and flattening-filter-free 7 MV beam line

et al. 2019

View full text Add to dashboard Cite

The aim of our work is to provide the up-to-now missing information on the Siemens Artiste FFF 7 MV beam line using a Monte-Carlo model fit to the realistic dosimetric measurements at the linear accelerator in clinical use at our department. The main Siemens Artiste 6MV and FFF 7MV beams were simulated using the Geant4 toolkit. The simulations were compared with the measurements with an ionization chamber in a water phantom to verify the validation of simulation and tuning the primary electron parameters. Hereafter, other parameters such as surface dose, spectrum, electron contamination, symmetry, flatness/unflatness, slope, and characteristic off-axis changes were discussed for both Flat and FFF mode. The mean electron energy for the FFF beam was 8.8 MeV and 7.5 MeV for Flat 6 MV, the spread energy and spot size of the selected Gaussian distribution source were 0.4 MeV and 1mm, respectively. The dose rate of the FFF beam was 2.8 (2.96) times higher than for the flattened beam for a field size of 10×10 (20×20) cm2. The electron contamination has significant contribution to the surface dose especially for the flattened beam. The penumbra, surface dose and the mean energy of photons decrease by removing the flattening filter. Finally, the results show that off-axis changes have no strong effect on the mean energy of FFF beams, while this effect was more considerable for the flattened beam.

show abstract

Evaluation of the dosimetric characteristics of 6 MV flattened and unflattened photon beam

Cited by 13 publications

References 21 publications

Increase in Superficial Dose in Whole-Breast Irradiation With Halcyon Straight-Through Linac Compared With Traditional C-arm Linac With Flattening Filter: In vivo Dosimetry and Planning Study

Increase in Superficial Dose in Whole-Breast Irradiation With Halcyon Straight-Through Linac Compared With Traditional C-arm Linac With Flattening Filter: In vivo Dosimetry and Planning Study

Medical X‐band linear accelerator for high‐precision radiotherapy

Monte-Carlo simulation of the Siemens Artiste linear accelerator flat 6 MV and flattening-filter-free 7 MV beam line

Contact Info

Product

Resources

About