CYCLOTRONS2022 - List of Authors (Baumgarten, C.)

Paper	Title	Page
TUAI01	Cyclotron Beam Extraction by Acceleration	110
	C. Baumgarten PSI, Villigen PSI, Switzerland
	One of the decisive issues in the design and operation of cyclotrons is the choice of the beam extraction method. Typical methods are extraction by electrostatic extractors and by stripping. The former method requires DC high voltage electrodes which are notorious for high-voltage breakdowns. The latter method requires beams of atomic or molecular ions which are notorious for rest gas and Lorentz stripping. We discuss the conditions to be met such that a charged particle beam will leave the magnetic field of an isochronous cyclotron purely by fast acceleration.
DOI •	reference for this paper ※ doi:10.18429/JACoW-CYCLOTRONS2022-TUAI01
About •	Received ※ 05 December 2022 — Revised ※ 09 January 2023 — Accepted ※ 09 July 2023 — Issue date ※ 16 July 2023
Cite •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WEAO01	OPAL Simulation on the Beam Transmission in the Central Region of the Medical Cyclotron COMET at Paul Scherrer Institute	148
	H. Zhang, C. Baumgarten, P. Frey, M. Hartmann, R. Kan, M. Kostezer, A. Mülhaupt, J.M. Schippers, A. Schmidt, J. Snuverink PSI, Villigen PSI, Switzerland
	The use of the medical cyclotron COMET for FLASH proton therapy requires a high beam transmission from the ion source through the central region apertures. This paper first presents a model of the COMET cyclotron featuring a rotatable ion source, a movable puller, and an adjustable first fixed slit (FFS), implemented with the OPAL framework. The electromagnetic field is individual-ly created to match each specific configuration. The beam optics parameters, especially beam position and beam size upon approaching and after passing FFS, have been studied in detail. The OPAL simulations demon-strate that an optimal configuration of the ion source, the puller and the FFS is key to achieve a high beam trans-mission. An experimental test gave a 2.8 times higher intensity within COMET cyclotron with the modifications derived on the basis of the simulations: a 0.57 mm shift of puller and a 5.6° rotation of ion source. The simula-tions indicate that, with these modifications, the beam can still be centered and accelerated to the extraction energy of 250 MeV. Next step is to investigate the influ-ence of such modifications upon the acceleration and the extraction, again with an iterative approach combining simulations and experiments.
	Slides WEAO01 [5.351 MB]
DOI •	reference for this paper ※ doi:10.18429/JACoW-CYCLOTRONS2022-WEAO01
About •	Received ※ 13 December 2022 — Revised ※ 09 January 2023 — Accepted ※ 01 February 2023 — Issue date ※ 11 March 2023
Cite •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WEBO05	Upgrade of a Clinical Facility to Achieve a High Transmission and Gantry Angle-Independent Flash Tune	191
	I. Colizzi, C. Baumgarten, A.L. Gabard, R. Künzi, A.L. Lomax, V. Maradia, D. Meer, S. Psoroulas, D.C. Weber PSI, Villigen PSI, Switzerland V. Maradia ETH, Zurich, Switzerland D.C. Weber University of Zurich, University Hospital, Zurich, Switzerland D.C. Weber KRO, Bern, Switzerland
	Funding: This work is supported by the SNF grant 200822 In proton therapy, FLASH-RT, irradiation at ultra-high dose rates (>40 Gy/s) that can minimize radiation-induced harm to healthy tissue without reducing its ability to treat tumors, is a topic of great interest. However, in cyclotron-based proton therapy facilities, losses caused by the energy degradation process reduce the transmission to less than 1% for low energies, making it difficult to achieve high dose rates over the clinical range (70-230 MeV). We will demonstrate how an already existing clinical beamline can be converted into a FLASH beamline by beam optic changes only. To achieve maximum transmission, we have developed a new optics that transports the undegraded 250 MeV beam from the cyclotron to the isocenter. However, this has asymmetric emittance in the transverse planes, leading to gantry angle-dependent beam characteristics at the patient. Particle transport has been simulated with MINT (in-house matrix multiplication transport program with Monte Carlo simulations for scattering effects) and benchmarked with beam profile measurements. We used the method of σ matrix matching (M. Benedikt et al. 1997) to achieve gantry angle-independent optics. MINT simulations and beam profile measurements showed a good agreement, and with FLASH optics, we experimentally achieved almost 90% transmission at the patient, translating to a maximum current of 720 nA (>9000 Gy/s). Further, we demonstrate that using the matrix matching optimization criteria together with fine-tuning of the magnets, we could achieve gantry angle-independent beam profiles at the patient location. In conclusion, we demonstrated how an already existing cyclotron-based proton gantry can be adapted to achieve ultra-high dose rates at 250 MeV, enabling investigations of FLASH radiotherapy with protons. Since most of the modifications are performed on the beam optics, it is entirely transparent to clinical operations, making the method transferable to other facilities.
	Slides WEBO05 [5.057 MB]
DOI •	reference for this paper ※ doi:10.18429/JACoW-CYCLOTRONS2022-WEBO05
About •	Received ※ 31 December 2022 — Revised ※ 10 January 2023 — Accepted ※ 01 February 2023 — Issue date ※ 10 July 2023
Cite •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

Paper

Title

Page

Cyclotron Beam Extraction by Acceleration

110

C. Baumgarten
PSI, Villigen PSI, Switzerland

One of the decisive issues in the design and operation of cyclotrons is the choice of the beam extraction method. Typical methods are extraction by electrostatic extractors and by stripping. The former method requires DC high voltage electrodes which are notorious for high-voltage breakdowns. The latter method requires beams of atomic or molecular ions which are notorious for rest gas and Lorentz stripping. We discuss the conditions to be met such that a charged particle beam will leave the magnetic field of an isochronous cyclotron purely by fast acceleration.

DOI •

reference for this paper ※ doi:10.18429/JACoW-CYCLOTRONS2022-TUAI01

About •

Received ※ 05 December 2022 — Revised ※ 09 January 2023 — Accepted ※ 09 July 2023 — Issue date ※ 16 July 2023

Cite •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WEAO01

OPAL Simulation on the Beam Transmission in the Central Region of the Medical Cyclotron COMET at Paul Scherrer Institute

148

H. Zhang, C. Baumgarten, P. Frey, M. Hartmann, R. Kan, M. Kostezer, A. Mülhaupt, J.M. Schippers, A. Schmidt, J. Snuverink
PSI, Villigen PSI, Switzerland

The use of the medical cyclotron COMET for FLASH proton therapy requires a high beam transmission from the ion source through the central region apertures. This paper first presents a model of the COMET cyclotron featuring a rotatable ion source, a movable puller, and an adjustable first fixed slit (FFS), implemented with the OPAL framework. The electromagnetic field is individual-ly created to match each specific configuration. The beam optics parameters, especially beam position and beam size upon approaching and after passing FFS, have been studied in detail. The OPAL simulations demon-strate that an optimal configuration of the ion source, the puller and the FFS is key to achieve a high beam trans-mission. An experimental test gave a 2.8 times higher intensity within COMET cyclotron with the modifications derived on the basis of the simulations: a 0.57 mm shift of puller and a 5.6° rotation of ion source. The simula-tions indicate that, with these modifications, the beam can still be centered and accelerated to the extraction energy of 250 MeV. Next step is to investigate the influ-ence of such modifications upon the acceleration and the extraction, again with an iterative approach combining simulations and experiments.

Slides WEAO01 [5.351 MB]

DOI •

reference for this paper ※ doi:10.18429/JACoW-CYCLOTRONS2022-WEAO01

About •

Received ※ 13 December 2022 — Revised ※ 09 January 2023 — Accepted ※ 01 February 2023 — Issue date ※ 11 March 2023

Cite •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WEBO05

Upgrade of a Clinical Facility to Achieve a High Transmission and Gantry Angle-Independent Flash Tune

191

I. Colizzi, C. Baumgarten, A.L. Gabard, R. Künzi, A.L. Lomax, V. Maradia, D. Meer, S. Psoroulas, D.C. Weber
PSI, Villigen PSI, Switzerland
V. Maradia
ETH, Zurich, Switzerland
D.C. Weber
University of Zurich, University Hospital, Zurich, Switzerland
D.C. Weber
KRO, Bern, Switzerland

Funding: This work is supported by the SNF grant 200822
In proton therapy, FLASH-RT, irradiation at ultra-high dose rates (>40 Gy/s) that can minimize radiation-induced harm to healthy tissue without reducing its ability to treat tumors, is a topic of great interest. However, in cyclotron-based proton therapy facilities, losses caused by the energy degradation process reduce the transmission to less than 1% for low energies, making it difficult to achieve high dose rates over the clinical range (70-230 MeV). We will demonstrate how an already existing clinical beamline can be converted into a FLASH beamline by beam optic changes only. To achieve maximum transmission, we have developed a new optics that transports the undegraded 250 MeV beam from the cyclotron to the isocenter. However, this has asymmetric emittance in the transverse planes, leading to gantry angle-dependent beam characteristics at the patient. Particle transport has been simulated with MINT (in-house matrix multiplication transport program with Monte Carlo simulations for scattering effects) and benchmarked with beam profile measurements. We used the method of σ matrix matching (M. Benedikt et al. 1997) to achieve gantry angle-independent optics. MINT simulations and beam profile measurements showed a good agreement, and with FLASH optics, we experimentally achieved almost 90% transmission at the patient, translating to a maximum current of 720 nA (>9000 Gy/s). Further, we demonstrate that using the matrix matching optimization criteria together with fine-tuning of the magnets, we could achieve gantry angle-independent beam profiles at the patient location. In conclusion, we demonstrated how an already existing cyclotron-based proton gantry can be adapted to achieve ultra-high dose rates at 250 MeV, enabling investigations of FLASH radiotherapy with protons. Since most of the modifications are performed on the beam optics, it is entirely transparent to clinical operations, making the method transferable to other facilities.

Slides WEBO05 [5.057 MB]

DOI •

reference for this paper ※ doi:10.18429/JACoW-CYCLOTRONS2022-WEBO05

About •

Received ※ 31 December 2022 — Revised ※ 10 January 2023 — Accepted ※ 01 February 2023 — Issue date ※ 10 July 2023

Cite •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)