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Spot Scanning Dose Delivery with Rapid Cycling Proton Beams From RCMS

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H Liu

C Cheng1 , H Liu2,3*, S Lee3 , (1) University Hospitals Case Medical Center, Cleveland, OH, (2) UT Southwestern Medical Center, Dallas, Texas, (3) Indiana University Bloomington, Bloomington, IN


SU-E-T-303 Sunday 3:00PM - 6:00PM Room: Exhibit Hall


A rapid cycling proton beam has several distinct characteristics superior to a slow extraction synchrotron: The beam energy and energy spread, beam intensity and spot size can be varied spot by spot. The feasibility of using a spot scanning beam from a rapidc-ycling-medical-synchrotron (RCMS) at 10 Hz repetition frequency is investigated in this study for its application in proton therapy.


The versatility of the beam is illustrated by two examples in water phantoms: (1) a cylindrical PTV irradiated by a single field and (2) a spherical PTV irradiated by two parallel opposed fields. A uniform dose distribution is to be delivered to the volumes. Geant4 Monte Carlo code is used to validate the dose distributions in each example.


Transverse algorithms are developed to produce uniform distributions in each transverse
plane in the two examples with a cylindrical and a spherical PTV respectively.
Longitudinally, different proton energies are used in successive transverse planes to
produce the SOBP required to cover the PTVs. In general, uniformity of dose
distribution within 3% is obtained for the cylinder and 3.5% for the sphere. The transverse
algorithms requires 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 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 existing spot scanning beams in proton therapy with better beam
control and lower neutron dose.

Funding Support, Disclosures, and Conflict of Interest: This work is supported in part by grants from the US Department of Energy under contract DE-FG02-12ER41800 and the National Science Foundation NSF PHY-1205431.

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