Beam transport system and particle beam therapy system

A beam transport system which comprises a beam shaping device by which a distribution profile of a charged particle beam having, at an end in a cross-sectional direction of the beam, a steep portion where a particle number varies steeply, is shaped into a moderated form;

• and which transports the charged particle beam to an irradiation target that is positioned so as to include an isocenter as a positional reference for irradiation;
• wherein, assuming that a direction perpendicular to a traveling direction of the charged particle beam and passing from a center of the charged particle beam to the steep portion is an x-direction, and inclinations of charged particles forming the charged particle beam with respect to the traveling direction, are angle components, the beam shaping device comprises:
• a pre-stage quadrupole electromagnet that reduces a distribution width of x-angle components that are the angle components in the x-direction in the charged particle beam;
• a penumbra expander that moderates an end profile of a particle-number distribution of the x-angle components in the charged particle beam having passed through the pre-stage quadrupole electromagnet;
• and
• a post-stage quadrupole electromagnet that adjusts a betatron phase in a phase-space distribution in the x-direction, of the charged particle beam having passed through the penumbra expander;
• and
• wherein the post-stage quadrupole electromagnet adjusts the betatron phase so that a phase advance angle thereof from the penumbra expander to the isocenter is in a range of an odd multiple of 90 degrees±45 degrees.