Particle beam therapy device and irradiation field forming method

1. A particle beam therapy device, comprising:

a scanning unit that performs scanning with a particle beam to form an irradiation field;

a shift unit that shifts the irradiation field by deflecting the particle beam emitted from the scanning unit to form an expanded irradiation field; and

a control unit that dynamically switches operation conditions of the scanning unit in a scanning period in which scanning with the particle beam is performed, and that statically switches operation conditions of the shift unit in an interruption period in which irradiation with the particle beam is not performed.

2. The particle beam therapy device according to claim 1 , wherein

the scanning unit includes:

a first scanning electromagnet that causes scanning with the particle beam in a first scanning direction orthogonal to a scanning central axial direction; and

a second scanning electromagnet that causes scanning with the particle beam in a second scanning direction orthogonal to the scanning central axial direction and the first scanning direction, and

the shift unit includes a first shift electromagnet that shifts the irradiation field in the first scanning direction.

3. The particle beam therapy device according to claim 2 , wherein

a settling time of a magnetic field formed by the first scanning electromagnet is shorter than a settling time of a magnetic field formed by the first shift electromagnet.

4. The particle beam therapy device according to claim 2 , wherein

inductance of the first scanning electromagnet is smaller than inductance of the first shift electromagnet.

5. The particle beam therapy device according to claim 2 , wherein

the number of shift stages in the first scanning direction in the shift unit is m (where m is an odd number of 3 or more).

6. The particle beam therapy device according to claim 2 , wherein

the shift unit includes a second shift electromagnet that shifts the irradiation field in the second scanning direction.

7. The particle beam therapy device according to claim 6 , wherein

the number of shift stages in the first scanning direction in the shift unit is m (where m is an odd number of 3 or more),

the number of shift stages in the second scanning direction in the shift unit is n (where n is an odd number of 3 or more), and

the expanded irradiation field is equivalent to a set of m×n irradiation field divisions.

8. The particle beam therapy device according to claim 1 , wherein

whether to shift the irradiation field is determined according to energy of the particle beam.

9. The particle beam therapy device according to claim 1 , further comprising:

a reference image forming unit that forms a reference image including a tissue image, wherein

the reference image includes a division image that is an image synthesized on the issue image and that represents a plurality of irradiation field divisions formed by shift of the irradiation field, and

the reference image is displayed in at least one of a treatment planning stage and a treatment stage.

10. An irradiation field forming method, comprising the steps of:

forming an irradiation field by performing scanning with a particle beam for treatment; and

forming an expanded irradiation field by shifting the irradiation field through deflecting the particle beam after the scanning;

dynamically switching operation conditions of the scanning in a scanning period in which the scanning with the particle beam is performed, and

statically switching operation conditions of the shifting in an interruption period in which irradiation with the particle beam is not performed.