Energy compensation of slow extracted beams with RF acceleration

In a conventional carbon-ion radiotherapy facility, a carbon-ion beam is typically accelerated up to an optimum energy, slowly extracted from a synchrotron ring by a resonant slow extraction method, and ultimately delivered to a patient through a beam-delivery system. At Japan’s Gunma University, a method employing slow-beam extraction along with beam-acceleration has been adopted. This method slightly alters the extracted-beam’s energy owing to the acceleration component of the process, which subsequently results in a residual-range variation of approximately 2 mm in water-equivalent length. However, this range variation does not disturb a distal dose distribution with broad-beam methods such as the single beam-wobbling method. With the pencil-beam 3D scanning method, however, such a range variation disturbs a distal dose distribution because the variation is comparable to slice thickness. Therefore, for pencil-beam 3D scanning, an energy compensation method for a slow extracted beam is proposed in this paper. This method can compensate for the aforementioned energy variances by controlling net energy losses through a rotatable energy absorber set fixed between the synchrotron exit channel and the isocenter. Experimental results demonstrate that beam energies can be maintained constant, as originally hypothesized. Moreover, energy-absorber positions were found to be significantly enhanced by optimizing beam optics for reducing beam-size growth by implementation of the multiple-scattering effect option

STUDY OF SCATTERER METHOD TO OMPENSATE ASYMMETRIC DISTRIBUTION OF SLOWLY EXTRACTED BEAM AT HIMAC SYNCHROTRON

In ion beam cancer therapy, it is generally essential for a scanning-irradiation method and a rotating gantry system to deliver a circular beam profile with a Gaussian distribution. A slow beam extraction method utilized in a synchrotron ring, however, can not deliver a beam with a Gaussian distribution in the horizontal phase space, because of its extraction mechanism. Thus, we haveproposed a thin scatterer method in order to compensate for the phase-space distribution of a slowly extracted beam, although the emittance is slightly enlarged by scattering. As a result of particle tracking, we verified thatthe proposed method could change an asymmetric distribution to a Gaussian one in the horizontal phase space and realize a symmetric beam condition for therotating gantry

STUDY OF SCATTERER METHOD TO COMPENSATE ASYMMETRIC DISTRIBUTION OF SLOWLY EXTRACTED BEAM AT HIMAC SYNCHROTRON

In ion beam cancer therapy, it is generally essential for a scanning-irradiation method and a rotating gantry system to deliver a circular beam profile with a Gaussian distribution. A slow beam extraction method utilized in a synchrotron ring, however, can not deliver a beam with a Gaussian distribution in the horizontal phase space, because of its extraction mechanism. Thus, we haveproposed a thin scatterer method in order to compensate for the phase-space distribution of a slowly extracted beam, although the emittance is slightly enlarged by scattering. As a result of particle tracking, we verified thatthe proposed method could change an asymmetric distribution to a Gaussian one in the horizontal phase space and realize a symmetric beam condition for therotating gantry

Development of superconducting wiggler at NIRS

EPAC 200