Patent Number: 
Section: claims

1. A method implemented on a computing device having at least one processor and at least one computer-readable storage medium for correcting position errors for a multi-leaf collimator (MLC), the MLC including a plurality of leaves to shape a radiation field, each of the plurality of leaves being associated with a driving component including a main encoder, the method comprising:determining a first position for each of the plurality of leaves, information associated with the first position including a first movement direction and a first angle, wherein a movement of the each of the plurality of leaves along the first movement direction is configured to move toward or away from a center of the radiation field;obtaining a first reference offset value associated with the first position of the each of the plurality of leaves from a pre-determined offset table;determining an offset value associated with the first position based on the first angle, the first movement direction, and the first reference offset value; anddetermining a target position of the each of the plurality of leaves based on the offset value. 2. The method of claim 1, wherein the determining a first position for each of the plurality of leaves includes:obtaining an angle of a gantry corresponding to the first position of the each of the plurality of leaves;obtaining an angle of a collimator corresponding to the first position of the each of the plurality of leaves, wherein the MLC is mounted in the collimator and rotates along with the collimator; anddetermining the first angle of the each of the plurality of leaves based on the angle of the gantry and the angle of the collimator. 3. The method of claim 1, wherein the determining a first position for each of the plurality of leaves includes:obtaining a first velocity relating to the driving component;in response to a determination that the first velocity relating to the driving component is lower than a first threshold, determining the first movement direction as a backward movement direction, the each of the plurality of leaves being configured to move away from the center of the radiation field along the backward movement direction; andin response to a determination that the first velocity relating to the driving component is greater than a second threshold, determining the first movement direction as a forward movement direction, the each of the plurality of leaves being configured to move toward the center of the radiation field along the forward movement direction. 4. The method of claim 1, wherein the determining a target position of the each of the plurality of leaves based on the offset value includes:subtracting the offset value from a preprogrammed position of the each of the plurality of leaves. 5. The method of claim 1, wherein the information associated with the first position includes a first main encoder value, the determining an offset value associated with the first position based on the first angle, the first movement direction, and the first reference offset value includes:obtaining a first main encoder value corresponding to the first position of the each of the plurality of leaves, the first main encoder value being acquired by the main encoder;obtaining a second main encoder value corresponding to a second position of the each of the plurality of leaves, the second main encoder value being acquired by the main encoder, and the second position being a position at where a movement direction of the each of the plurality of leaves changes from a second movement direction to the first movement direction; anddetermining the offset value associated with the first position based on the first movement direction, the first reference offset value, and a difference between the first main encoder value and the second main encoder value. 6. The method of claim 5, wherein the determining the offset value associated with the first position based on the first movement direction, the first reference offset value, and a difference between the first main encoder value and the second main encoder value includes:if the each of the plurality of leaves moves away from the center of the radiation field along the first movement direction, designating a minimum value among the first reference offset value and a sum of a second reference offset value associated with the second position and the difference between the first main encoder value and the second main encoder value as the offset value associated with the first position; andif the each of the plurality of leaves moves toward the center of the radiation field along the first movement direction, designating a maximum value among the first reference offset value and a sum of the second reference offset value associated with the second position and the difference between the first main encoder value and the second main encoder value as the offset value associated with the first position. 7. The method of claim 1, wherein the determining an offset value associated with the first position based on the first angle, the first movement direction, and the first reference offset value includes:if the each of the plurality of leaves moves toward the center of the radiation field along the first movement direction and the first angle is equal to 0 degrees, designating the offset value associated with the first position as 0. 8. The method of claim 1, wherein the determining a target position of the each of the plurality of leaves based on the offset value includes:obtaining a first main encoder value corresponding to a first position of each of the plurality of leaves acquired by the main encoder; andcorrecting the first main encoder value based on the offset value to obtain the target position of the each of the plurality of leaves. 9. The method of claim 8, wherein the correcting the first main encoder value based on the offset value includes:adding the offset value to the first main encoder value to obtain the target position of the each of the plurality of leaves. 10. A method implemented on a computing device having at least one processor and at least one computer-readable storage medium for correcting position errors for a multi-leaf collimator (MLC), the MLC including a plurality of leaves to shape a radiation field, each of the plurality of leaves being associated with a driving component including a main encoder, the method comprising:determining a first position for each of the plurality of leaves, information associated with the first position including a first movement phase, wherein a movement of the each of the plurality of leaves moves in the first movement phase is configured to move toward or away from a center of the radiation field;determining an offset value associated with the first position based on the first movement phase; anddetermining a target position of the each of the plurality of leaves based on the offset value;wherein the first movement phase associated with the first position of each of the plurality of leaves is determined based on a difference between a first measurement value and a second measurement value acquired by one of the main encoder and an auxiliary encoder in two adjacent sampling periods. 11. The method of claim 10, whereinthe first measurement value corresponds to the first position, the auxiliary encoder is associated with each of the plurality of leaves and configured to determine a position of each of the plurality of leaves; andthe first movement phase includes one of:a first phase in which the each of the plurality of leaves is moving toward the center of the radiation field;a second phase in which the each of the plurality of leaves is static relative to a carriage of the MLC and is directed to move away from the center of the radiation field;a third phase in which the each of the plurality of leaves is moving away from the center of the radiation field; anda fourth phase in which the each of the plurality of leaves is static relative to the carriage of the MLC and is directed to move toward the center of the radiation field. 12. The method of claim 11, wherein the determining an offset value associated with the first position based on the first movement phase includes:in response to a determination that the first movement phase is the second phase or the fourth phase, determining a reference offset value associated with a second position of the each of the plurality of leaves, the second position corresponding to a position at where a movement phase of the each of the plurality of leaves changes from a second movement phase to the first movement phase;obtaining a first main encoder value corresponding to the first position of the each of the plurality of leaves, the first main encoder value being acquired by the main encoder;obtaining a second main encoder value corresponding to the second position of the each of the plurality of leaves, the second main encoder value being acquired by the main encoder; anddetermining the offset value associated with the first position based on a difference between the first main encoder value and the second main encoder value and the reference offset value associated with the second position. 13. The method of claim 11, wherein the determining an offset value associated with the first position based on the first movement phase includes:in response to a determination that the first movement phase is the first phase or the third phase, the offset value associated with the first position is constant. 14. The method of claim 13, wherein the offset value associated with the first position is equal to a reference offset value associated with a second position at where a movement phase of the each of the plurality of leaves changes from a second movement phase to the first movement phase. 15. The method of claim 14, further comprising:determining whether an angle change value of the each of the plurality of leaves between the first position and the second position exceeds a preprogrammed threshold, the information associated with the first position including a first angle; andin response to a determination that the angle change value exceeds the preprogrammed threshold, correcting the offset value associated with the first position of the each of the plurality of leaves. 16. The method of claim 14, further comprising:obtaining a first main encoder value and a first auxiliary encoder value corresponding to the first position of the each of the plurality of leaves, the first main encoder value being acquired by the main encoder, the first auxiliary encoder value being acquired by the auxiliary encoder;obtaining a second main encoder value and a second auxiliary encoder value corresponding to the second position, the second main encoder value being acquired by the main encoder, the second auxiliary encoder value being acquired by the auxiliary encoder;determining a first difference between the first main encoder value and the second main encoder value;determining a second difference between the first auxiliary encoder value and the second auxiliary encoder value;determining whether the offset value associated with the first position needs to be corrected based on the first difference and the second difference; andcorrecting the offset value associated with the first position of the each of the plurality of leaves. 17. The method of claim 15, wherein the first angle of each of the plurality of leaves is determined by:obtaining an angle of a gantry corresponding to the first position of the each of the plurality of leaves;obtaining an angle of a collimator corresponding to the first position of the each of the plurality of leaves, wherein the MLC is mounted in the collimator and rotates along with the collimator; anddetermining the first angle of the each of the plurality of leaves based on the angle of the gantry and the angle of the collimator. 18. The method of claim 11, wherein the information of the first position includes a first angle, and if the first movement phase is the first phase and the first angle is equal to 0 degrees, the offset value associated with the first position is equal to 0. 19. The method of claim 10, wherein the determining a target position of the each of the plurality of leaves based on the offset value includes:subtracting the offset value from a preprogrammed position of the each of the plurality of leaves. 20. A system for correcting position errors for a multi-leaf collimator (MLC), the MLC including a plurality of leaves to shape a radiation field, each of the plurality of leaves being associated with a driving component including a main encoder, the system comprising:at least one storage device storing executable instructions, andat least one processor in communication with the at least one storage device, when executing the executable instructions, causing the system to:determine a first position for each of the plurality of leaves, information associated with the first position including a first movement direction and a first angle, wherein the each of the plurality of leaves moves toward or away from a center of the radiation field along the first movement direction;obtain a first reference offset value associated with the first position of the each of the plurality of leaves from a pre-determined offset table;determine an offset value associated with the first position based on the first angle, the first movement direction, and the first reference offset value; anddetermine a target position of the each of the plurality of leaves based on the offset value.