Spot scanning with a rapid cycling proton beam: Dose delivery algorithms

Chee-Wai Cheng, Honghuan Liu, Shyh-Yuan Lee


A rapid cycling proton beam has several distinct characteristics that are superior to a slow extraction synchrotron: the beam energy and energy spread, beam intensity and spot size can be controlled and varied spot by spot. In this study, we demonstrate the feasibility of using a spot scanning beam from a rapid-cycling-medical-synchrotron (RCMS) at 10 Hz repetition frequency in proton therapy. The versatility of the RCMS beam in proton therapy is illustrated by two examples: (1) a cylindrical volume embedded in a water phantom irradiated by a single field and (2) a spherical volume in a water phantom irradiated by two parallel opposed fields. A uniform dose distribution is to be delivered to the volumes. The Monte Carlo code, Geant4, is used to validate the dose distributions in each example. Monte Carlo codes can also be used in actual treatment plans to optimize beam spot distributions. Transverse delivery algorithms are developed to produce uniform distributions in each transverse plane in the two examples. Longitudinally, different proton energies are used in successive transverse planes to produce the SOBP required to cover the volumes.  In general, uniformity of dose distribution within 3% is obtained for the cylinder and 3.5% for the sphere. The transverse algorithms require only few hundred beam spots for each plane. The algorithms may be applied to larger volumes by increasing the intensity spot by spot for the same delivery time of the same dose. The treatment time can be made shorter than 1 minute for any field configuration and tumor shape. The unique beam characteristics of a spot scanning beam from a RCMS at 10 Hz repetition frequency are used to design transverse and longitudinal algorithms to produce uniform distribution for any arbitrary shape and size of targets. The proposed spot scanning beam is more versatile than the existing spot scanning beams in proton therapy with better beam control and lower neutron dose.


Rapid cycling synchrotron, Proton therapy, Spot scanning, Delivery algorithm, IMPT

Full Text:



Kostjuchenko J, Nichiporov D, Luckjashin V. A compact ridge filter for spread out Bragg peak production in pulsed proton clinical beams. Med Phys. 2001;28:1427-30.

Farr JB, Mascia AE, Hsi WC, et al. Clinical characterization of a proton beam continuous uniform scanning system with dose layer stacking. Med Phys. 2008;35:4945-54.

Nichiporov D, Hsi W, Farr F. Beam characteristics in two different proton uniform scanning systems: A side-by-side comparison. Med Phys. 2012;39:2559-68.

Gillin MT, Sahoo N, Bues M, et al. Commissioning of the discrete spot scanning proton beam delivery system at the University of Texas MD Anderson Cancer Center, Proton Therapy Center, Houston. Med Phys. 2010;37:154-63.

Pedroni E, Bacher R, Blattmann H, et al. The 200 MeV proton therapy project at the Paul Scherer Institute: Conceptual design and practical realization. Med Phys. 1995;22:37-53.

Lin S, Boehringer T, Coray A, et al. More than 10 years experience of beam monitoring with the Gantry 1 spot scanning proton therapy facility at PSI. Med Phys. 2009;36:5331-40.

Grevillot L, Bertrand D, Dessy F, et al. A Monte Carlo pencil beam scanning model for proton treatment plan simulation using GATE/GEANT4. Phys Med Biol. 2011;56:5203-19.

Peggs S, Barton D, Beebe-Wang J. et al. The rapid cycling medical synchrotron, RCMS. Proceedings of European Particle Accelerator Conference, Paris, France. 2002: 2754-56.

Peggs S, Cardona J, Brennan M, et al. RCMS - A second generation medical synchrotron. Proceedings of the 2001 Particle Accelerator Conference, Chicago. 2001:2482-84.

Cardona J, Kewisch J, Peggs S. Design of the RCMS lattice optics. Proceedings of EPAC, Paris, France. 2002:557-59.

Trbojevic D, Alessi J, Blaskiewicz M. et. al. Lattice design of a rapid cycling medical synchrotron for carbon/proton therapy. Proceedings of International Particle Accelerator Conference, San Sebastián, Spain. 2011:2541-43.

Peggs S. (editor), Pre-Conceptual Design of a Rapid Cycling Medical Synchrotron, C-A/AP/6, BNL. 1999.

Agostinelli S, Allison J, Amako K. et al. Geant4—a simulation toolkit. Nuclear Instruments and Methods in Physics Research. 2003;A 506:250-303.


Copyright (c) 2016 Chee-Wai Cheng, Honghuan Liu, Shyh-Yuan Lee

Creative Commons License
This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.


© Journal of Proton Therapy (ISSN 2469-5491)

To make sure that you can receive messages from us, please add the '' and '' domains to your e-mail 'safe list'. If you do not receive e-mail in your 'inbox', please check your 'bulk mail' or 'junk mail' folders.