Optimization algorithm for balancing quality and irradiation efficiency of proton arc treatment plan

Abstract

The invention discloses an optimization algorithm for balancing the plan quality and irradiation efficiency of proton arc therapy, and belongs to the field of radiotherapy, and the optimization algorithm comprises the steps: S1, reading the image and structure data of a patient; s2, generating a beam spot position according to the patient image and the structure data; s3, setting clinical requirements, including target region prescription dose, organ-endangering dose limit value, weight of each objective function item and weight of constraint conditions; s4, a dose calculation engine is called, dose distribution under current beam parameters is calculated, and the beam parameters comprise an energy layer, a beam spot position and a beam spot weight; and S5, continuously updating beam parameters according to an objective function and constraints by adopting an optimization algorithm in combination with machine parameter limitation, and searching an optimal solution in a beam parameter space. An optimization algorithm is adopted, the dose and the irradiation efficiency are directly combined, the rack rotation speed, the energy layer switching and the beam spot scanning time are considered in the calculated irradiation time, the contradiction between the proton arc treatment plan quality and the irradiation efficiency is allowed to be directly optimized and processed, and a proper plan is selected according to the clinical background.

Description

Technical Field

[0001] The present invention relates to the field of radiotherapy, and in particular to an optimization algorithm for balancing proton arc therapy plan quality and irradiation efficiency. Background Art

[0002] Proton arc therapy (PAT) uses a rotating gantry to deliver continuous irradiation at multiple angles. Combining the physical advantages of proton therapy with the geometric advantages of arc therapy, it can achieve better dose distribution and relative biological effects than intensity-modulated proton therapy, greater treatment robustness, and a similar or lower risk of secondary cancers, potentially further improving proton therapy efficiency. The most significant feature of PAT is the synchronization of proton beam delivery and gantry rotation during irradiation. However, the rotational inertia of the PAT gantry is significant, and its rotational speed and acceleration are strictly limited. Furthermore, to fully cover the target volume, proton therapy systems require the use of protons with a variety of energies and beam spot positions. The non-instantaneous switching of energy and beam spot positions increases irradiation time. Consequently, plan quality and irradiation efficiency are conflicting objectives. Currently, it is unclear to what extent irradiation efficiency and plan quality can achieve an ideal balance. To improve the irradiation efficiency of treatment plans while ensuring their quality, treatment plan information (gantry angle, beam energy, beam spot position, and beam intensity, etc.) and machine parameter limitations (maximum gantry rotation speed and acceleration, energy layer switching time, magnet scanning speed, and beam intensity, etc.) must be optimally integrated to produce an optimal treatment plan with high quality and irradiation efficiency.

[0003] So far, there is no optimization algorithm that can balance the quality of proton arc therapy plans and the hardware limitations of proton therapy equipment. Therefore, there is an urgent need for an optimization algorithm to balance the contradiction between plan quality and irradiation efficiency. Summary of the Invention

[0004] The present invention aims to overcome the shortcomings of the prior art in that it is difficult to balance the contradiction between plan quality and hardware limitations of proton therapy equipment, and provides an optimization algorithm for balancing proton arc therapy plan quality and irradiation efficiency.

[0005] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0006] An optimization algorithm for balancing proton arc therapy plan quality and irradiation efficiency includes the following steps:

[0007] S1: read patient images and structural data;

[0008] S2: generating a beam spot position according to the patient image and structural data;

[0009] S3: Set clinical requirements, including target volume prescription dose, organ-at-risk dose limit, and weights for each objective function term and constraint condition;

[0010] S4: calling a dose calculation engine to calculate the dose distribution under the current beam parameters, wherein the beam parameters include: energy layer, beam spot position, and beam spot weight;

[0011] S5: Combined with the machine parameter limitations, an optimization algorithm is used to continuously update the beam parameters according to the objective function and constraints, and the optimal solution is searched in the beam parameter space;

[0012] The objective function of the optimization algorithm is:

[0013] Obj Total =γ1×Obj Dose +γ2×Obj MP

[0014] Where: γ is the weight factor of each objective function, Obj MP is the objective function of equipment irradiation efficiency, Obj Dose is the dose objective function.

[0015] As a preferred embodiment of the present invention, the calculation formula of the objective function of the equipment irradiation efficiency is:

[0016]

[0017] Where: f is the weight factor, N is the number of arc control points of the proton therapy device, θ represents the angle of the arc control point of the proton therapy device, v max is the maximum rotational speed allowed by the device.

[0018] As a preferred embodiment of the present invention, the calculation formula for the irradiation time is:

[0019] T BDTi =T LSW +T SSpi +T SSw

[0020] Among them, T LSW is the energy layer switching time, T SSw is the magnet scanning speed, T LSW and T SSw are the intrinsic parameters of the proton accelerator, T SSpi is the parameter to be optimized related to the beam intensity.

[0021] As a preferred embodiment of the present invention, when the dose objective function is a quadratic objective function, the calculation formula is:

[0022]

[0023] Where: p is the anatomical structure weight, Dose i，pre The prescribed dose for the target area or the dose limit for the organ at risk, Dose i，TAR(OARs) is the dose value of the i-th element, H is the step function, for the target area, when Dose i，TAR <Dose i，pre 1 when Dose is high, otherwise 0. i，OARS >Dose i,pre 1 if yes, 0 otherwise.

[0024] As a preferred embodiment of the present invention, the three-dimensional dose distribution calculation formula is:

[0025] Dose=∑T SSp ×InfMax

[0026] Among them, T SSp is the irradiation time of the beam spot, and InfMax is the dose influence matrix of the beam spot per unit time in three-dimensional space.

[0027] Compared with the prior art, the advantages of the present invention are:

[0028] Using a new PAT plan optimization algorithm, dose and irradiation efficiency are directly combined. The irradiation time calculated by this patent takes into account the gantry rotation speed, energy layer switching, and beam spot scanning time. This allows users to directly optimize the conflict between proton arc therapy plan quality and irradiation efficiency and select an appropriate plan based on the clinical context. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Various other advantages and benefits will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiment below. The accompanying drawings are for illustration purposes only and are not to be considered as limiting the present invention. Throughout the drawings, the same reference numerals are used to denote the same components. In the drawings:

[0030] Figure 1 This is a flow chart of an optimization algorithm for balancing proton arc therapy plan quality and irradiation efficiency according to Example 1 of the present invention. DETAILED DESCRIPTION

[0031] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of the embodiments. The components of the embodiments of the present invention generally described and shown in the drawings herein can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without making creative work are within the scope of protection of the present invention.

[0032] It should be noted that similar numbers and letters represent similar items in the following figures. Therefore, once an item is defined in one figure, it does not need to be further defined or explained in subsequent figures. At the same time, in the description of the present invention, the terms "first" and "second" are used only to distinguish the description and should not be understood as indicating or implying relative importance, or implying any actual relationship or order between these entities or operations. In addition, the terms "connected" and "connected" can refer to direct connection between components or indirect connection through other components.

[0033] Example 1

[0034] An optimization algorithm for balancing proton arc therapy plan quality and irradiation efficiency, such as Figure 1 As shown, the following steps are included:

[0035] S1: read patient images and structural data;

[0036] S2: generating a beam spot position according to the patient image and structural data;

[0037] S3: Set clinical requirements, including target volume prescription dose, organ-at-risk dose limit, and weights for each objective function term and constraint condition;

[0038] S4: calling a dose calculation engine to calculate the dose distribution under the current beam parameters, wherein the beam parameters include: energy layer, beam spot position, and beam spot weight;

[0039] S5: Use optimization algorithms to continuously update beam parameters and search for the optimal solution in the beam parameter space.

[0040] Specifically, calculate the irradiation time:

[0041] In the present invention, each control point is used to balance the irradiation time (T BDTi ) including the energy layer switching time (T LSW ), beam spot irradiation time (TSSp ) and beam position switching time (T SSw ).

[0042] T BDTi =T LSW +T SSpi +T SSw (1)

[0043] Among them, T LSW and T SSw is the intrinsic parameter of the proton accelerator, T SSpi is the parameter to be optimized.

[0044] In the PAT system, given the initial velocity v of the i-th control point i and final velocity v i+1 , the adjacent angles of control points (θ i ,θ i+1 ), that is, the acceleration a i It should be limited to a certain range.

[0045]

[0046] where v i <v max ;a i <a max .

[0047] It can be seen from formula (2) that the optimization problem of irradiation time is to find the optimal rotation speed of each control point limited by the gantry rotation speed and acceleration parameters.

[0048] The actual rotation speed v should be close to the maximum rotation speed v allowed by the equipment max In addition, to ensure the accuracy of irradiation and the feasibility of the plan, the difference between the gantry rotation speeds in two adjacent beam directions should be minimized, that is, the value of a is minimized.

[0049] By optimizing the irradiation time of each control point (T BDT ) as low as possible and keep it constant, the above ideal state can be achieved. BDT May affect the quality of treatment plans.

[0050] Based on the above considerations, this patent intends to define the objective function of equipment irradiation efficiency as:

[0051]

[0052] Where: f is the weight factor, N is the number of arc control points of the proton therapy device, θ represents the angle of the arc control point of the proton therapy device, v maxis the maximum rotational speed allowed by the device.

[0053] Based on the above foundation, the objective function of an optimization algorithm that can handle the balance between the quality of proton arc therapy plans and the hardware limitations of proton therapy equipment can be expressed as:

[0054] Obj Total =γ1×Obj Dose +γ2×Obj MP (4)

[0055] Where: γ is the weight factor of each objective function, Obj Dose is the dose objective function.

[0056] Example 2

[0057] This embodiment is a preferred calculation method for the dose objective function in the optimization algorithm for balancing the proton arc therapy plan quality and irradiation efficiency described in the first embodiment;

[0058] There are many methods for calculating the dose objective function. Taking the common quadratic objective function as an example, the following calculation method is used:

[0059] Obj Dose =∑ i∈TAR p TAR ·H TAR ·(Dose i，pre -Dose i，TAR ) 2 +∑ i∈OARs p OARs ·H OARs ·(Dose i，pre -RDose i，OARS ) 2 (5)

[0060] Where: p is the anatomical structure weight, Dose i，pre The prescribed dose for the target area or the dose limit for the organ at risk, Dose i，TAR(OARs) is the dose value of the i-th element, H is the step function, for the target area, when Dose i，TAR <Dose i，pre 1 when Dose is high, otherwise 0. i，OARS >Dose i，pre 1 if yes, 0 otherwise.

[0061] The three-dimensional dose distribution can be calculated by the following formula:

[0062] Dose=∑T SSp ×InfMax (6)

[0063] Among them, T LSW is the energy layer switching time, T SSw is the magnet scanning speed, T LSW and T SSw are the intrinsic parameters of the proton accelerator, T SSpi is the parameter to be optimized related to the beam intensity.

[0064] Although formula (4) contains multiple sub-objective functions, they all optimize the variable of beam weight (TSSp), which can be solved by existing optimization algorithms and can be completed by the optimizer of any treatment planning system.

[0065] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any appropriate manner without contradiction. In order to avoid unnecessary repetition, the present disclosure will not further describe various possible combinations.

[0066] In addition, the various embodiments of the present disclosure may be arbitrarily combined, and as long as they do not violate the concept of the present disclosure, they should also be regarded as the contents disclosed by the present disclosure.

Claims

1. An optimization algorithm for balancing proton arc therapy plan quality and irradiation efficiency, characterized in that: The following steps are involved: S1: read patient images and structural data; S2: generating a beam spot position according to the patient image and structural data; S3: Set clinical requirements, including target volume prescription dose, organ-at-risk dose limit, and weights for each objective function term and constraint condition; S4: calling a dose calculation engine to calculate the dose distribution under the current beam parameters, wherein the beam parameters include: energy layer, beam spot position, and beam spot weight; S5: Combined with the machine parameter limitations, the optimization algorithm is used to continuously update the beam parameters and search for the optimal solution in the beam parameter space; The objective function of the optimization algorithm is: Obj Total =γ1×Obj Dose +γ2×Obj MP Where: γ is the weight factor of each objective function, Obj MP is the objective function of equipment irradiation efficiency, Obj Dose is the dose objective function.

2. The optimization algorithm for balancing proton arc therapy plan quality and irradiation efficiency according to claim 1, characterized in that: The calculation formula of the objective function of the equipment irradiation efficiency is: Where: f is the weight factor, N is the number of arc control points of the proton therapy device, θ represents the angle of the arc control point of the proton therapy device, v max is the maximum rotational speed allowed by the device.

3. The optimization algorithm for balancing proton arc therapy plan quality and irradiation efficiency according to claim 2, characterized in that: The calculation formula of the irradiation time is: T BDTi =T LSW +T SSpi +T SSw Among them, T LSW is the energy layer switching time, T SSw is the magnet scanning speed, T LSW and T SSw are the intrinsic parameters of the proton accelerator, T SSpi is the parameter to be optimized related to the beam intensity.

4. The optimization algorithm for balancing proton arc therapy plan quality and irradiation efficiency according to claim 1, characterized in that: When the dose objective function is a quadratic objective function, the calculation formula is: Where: p is the anatomical structure weight, Dose i，pre The prescribed dose for the target area or the dose limit for the organ at risk, Dose i,TAR(OARs) is the dose value of the i-th element, H is the step function, for the target area, when Dose i,TAR <Dose i，pre 1 when Dose is high, otherwise 0. i,OARS >Dose i,pre 1 if yes, 0 otherwise.

5. The optimization algorithm for balancing proton arc therapy plan quality and irradiation efficiency according to claim 4, characterized in that: The three-dimensional dose distribution calculation formula is: Dose=∑T SSp ×InfMax Among them, T SSp is the irradiation time of the beam spot, and InfMax is the dose influence matrix of the beam spot per unit time in three-dimensional space.

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