Concept of scanning magnet with distributed winding coils for particle beam therapy

Abstract

To reduce the size of a rotating gantry for a particle therapy system, it is desirable to reduce the size of the scanning system by substituting separated scanning magnets with a combined-function scanning magnet. A two-dimensionally designed scanning magnet with distributed winding coils (DW-SCM) is proposed. The DW-SCM can generate a rotating dipole magnetic field using a single power supply. The two-dimensional static magnetic field distributions of the DW-SCM were calculated using poisson superfish code and compared with those of an octupole scanning magnet (CW-SCM) and cos-theta-type scanning magnet ($\mathrm{Cos}\ensuremath{\theta}$-SCM) with the same bore diameter of 98 mm. The calculated two-dimensional magnetic field showed that the DW-SCM had the highest magnetic field strength of the three types of scanning magnets, and compared with the CW-SCM, the DW-SCM was 129% higher and the $\mathrm{cos}\text{ }\ensuremath{\theta}$-SCM was 72% higher. The good field region (radius) of field homogeneity within $\ifmmode\pm\else\textpm\fi{}0.5%$ of the DW-SCM had a symmetrical shape centered on a current phase of 30\ifmmode^\circ\else\textdegree\fi{}, and the minimum value was 24 mm. Also compared with the CW-SCM, the minimum good field region was 11% higher for the DW-SCM and 65% higher for the $\mathrm{cos}\text{ }\ensuremath{\theta}$-SCM. The results indicate that the proposed scanning magnet could generate a high-strength rotating dipole magnetic field, and it might be possible to reduce the size of a scanning system by substituting separated scanning magnets with the DW-SCM.