MC modeling method and equipment based on solid water

Abstract

The invention discloses an MC modeling method and equipment based on solid water, and the method comprises the steps: carrying out the dose detection through a solid water measurement block, and recording a plurality of groups of dose data; calculating to obtain a PDD curve and an OAR curve of the linear accelerator based on the multiple groups of dose data; and based on the PDD curve and the OAR curve, performing MC modeling by using a PSL model. Solid water is used for replacing a water tank to measure PDD and OAR of beams, a PSL model is used for MC modeling, only PDD and OAR are needed for dose measurement, and three-dimensional dose distribution is not needed. The method is simple and has universality.

Description

Technical Field

[0001] The present invention belongs to the technical field of MC modeling, and in particular relates to a MC modeling method and equipment based on solid water. Background Art

[0002] Tumor radiotherapy is a local treatment method that uses radiation to treat tumors. Most cancer patients need radiotherapy during the treatment of cancer. The role and status of radiotherapy in tumor treatment are becoming increasingly prominent, and it has become one of the main means of treating malignant tumors. As a commonly used medical device for radiotherapy, linear accelerators can generate high-energy X-rays and electron beams, with high dose rate, short irradiation time, large irradiation field, good dose uniformity and stability, and small penumbra area.

[0003] Monte Carlo (MC) simulation is generally considered to be the most accurate method for calculating radiation dose. For external irradiation, the accuracy of the overall calculation consists of two parts, namely the accelerator beam model and the transport of particles in the patient. Therefore, it is very important for clinical use to adjust the MC beam model according to the accelerator beam.

[0004] It is a common method to adjust the MC dose model using the phase space file obtained from the accelerator head simulation. Many MC methods directly use phase space files for modeling, such as DOSXYZnrc, MCNP, and VMC++. However, it is difficult to directly adjust the phase space file and correspond it to the measured data. Summary of the invention

[0005] In order to solve the above technical problems, the present invention proposes a MC modeling method and equipment based on solid water.

[0006] In order to achieve the above object, the technical solution of the present invention is as follows:

[0007] In one aspect, the present invention discloses a MC modeling method based on solid water, comprising:

[0008] Step S1: Use a solid water measuring block to perform dose detection and record multiple sets of dose data;

[0009] Step S2: based on multiple sets of dose data, calculating the PDD curve and OAR curve of the linear accelerator;

[0010] Step S3: Based on the PDD curve and OAR curve, MC modeling is performed using the PSL model.

[0011] Based on the above technical solution, the following improvements can be made:

[0012] As a preferred solution, step S1 includes:

[0013] Step S1.1: assembling a number of solid water sub-blocks to form a solid water measurement block;

[0014] Step S1.2: placing a solid water measuring block on the treatment bed and at the measuring position of the linear accelerator, and placing a detector inside the solid water measuring block;

[0015] Step S1.3: The linear accelerator starts detection and records multiple sets of dose data.

[0016] As a preferred solution, in step S2, based on multiple groups of dosage data, the following formula (1) is used for fitting to obtain a PDD curve;

[0017]

[0018] Among them: k, n, μ are fitting parameters;

[0019] D is the thickness of the solid water measuring block.

[0020] As a preferred solution, step S3 includes the following contents:

[0021] The photon PSL is divided according to position and energy (m, n, e), where (m, n) marks the plane position perpendicular to the central axis of the beam and e refers to the energy;

[0022] The modeling problem can be described as solving equation (2);

[0023] Ax=b(2)

[0024] Among them, x is the weight of the PSL corresponding to each (m, n, e);

[0025] A is the PDD and OAR calculated in the solid water measurement block for each unit weight of PSL;

[0026] B is the PDD and OAR measured in the solid water measurement block;

[0027] Assuming that the beam is symmetric and smooth about the central axis, the following problem is obtained:

[0028]

[0029] in, is a function of radius r and energy e;

[0030] B is a linear algorithm, which is used to define the Expanded to two dimensions

[0031] and is the gradient operator;

[0032] The weight of the photon is obtained by solving (3);

[0033] For electrons, all electrons in the phase space file are considered as effective PSLs;

[0034] The effective PSL dose of unit weight in solid water is calculated in advance, and the measured dose is used to solve the effective PSL weight x using equation (4): e ;

[0035]

[0036] Among them, p e is the unit weighted effective PSL dose in the built-up area of ​​solid water;

[0037] p p is the dose calculated by the photon model obtained by equation (3);

[0038] p b is the measured dose;

[0039] <·|·> represents the inner product of vectors.

[0040] In addition, on the other hand, the present invention also discloses a solid water-based MC modeling device, comprising:

[0041] A dose data acquisition module is used to perform dose detection using a solid water measuring block and record multiple sets of dose data;

[0042] A curve calculation module, used to calculate the PDD curve and OAR curve of the linear accelerator based on multiple sets of dose data;

[0043] The MC modeling module is used to perform MC modeling using the PSL model based on the PDD curve and the OAR curve.

[0044] As a preferred solution, the dose data acquisition module includes:

[0045] A splicing unit, used for assembling a plurality of solid water sub-blocks to form a solid water measuring block;

[0046] A placement unit is used to place the solid water measurement block on the treatment bed and at the measurement position of the linear accelerator, and to place the detector inside the solid water measurement block;

[0047] The detection unit is used to start the linear accelerator detection and record multiple sets of dose data.

[0048] As a preferred solution, in step S2, based on multiple groups of dosage data, the following formula (1) is used for fitting to obtain a PDD curve;

[0049]

[0050] Among them: k, n, μ are fitting parameters;

[0051] D is the thickness of the solid water measuring block.

[0052] As a preferred solution, the MC modeling module is used to perform the following method:

[0053] The photon PSL is divided according to position and energy (m, n, e), where (m, n) marks the plane position perpendicular to the central axis of the beam and e refers to the energy;

[0054] The modeling problem can be described as solving equation (2);

[0055] Ax=b(2)

[0056] Among them, x is the weight of the PSL corresponding to each (m, n, e);

[0057] A is the PDD and OAR calculated in the solid water measurement block for each unit weight of PSL;

[0058] B is the PDD and OAR measured in the solid water measurement block;

[0059] Assuming that the beam is symmetric and smooth about the central axis, the following problem is obtained:

[0060]

[0061] in, is a function of radius r and energy e;

[0062] B is a linear algorithm, which is used to define the Expanded to two dimensions

[0063] and is the gradient operator;

[0064] The weight of the photon is obtained by solving (3);

[0065] For electrons, all electrons in the phase space file are considered as effective PSLs;

[0066] The effective PSL dose of unit weight in solid water is calculated in advance, and the measured dose is used to solve the effective PSL weight x using equation (4): e ;

[0067]

[0068] Among them, p eis the unit weighted effective PSL dose in the built-up area of ​​solid water;

[0069] p p is the dose calculated by the photon model obtained by equation (3);

[0070] p b is the measured dose;

[0071] <·|·> represents the inner product of vectors.

[0072] The present invention discloses a MC modeling method and device based on solid water, which has the following beneficial effects:

[0073] First, solid water is used instead of a water tank to measure the PDD and OAR of the beam. Since solid water is low-cost, easy to obtain and easy to preserve, it can achieve the functions of a water tank while avoiding the problems that exist in the water tank, making accelerator modeling more convenient.

[0074] Second, a small amount of dose data is used for fitting to obtain the PDD curve, which can obtain all the data required for modeling, and is highly efficient.

[0075] Third, the present invention adopts the PSL model for MC modeling, and only PDD and OAR are needed to measure the dose, and no three-dimensional dose distribution is required. The method is simple and universal. BRIEF DESCRIPTION OF THE DRAWINGS

[0076] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0077] Figure 1 A flowchart of the MC modeling method provided for an embodiment of the present invention is shown today. DETAILED DESCRIPTION

[0078] The preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0079] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0080] The expression of “comprising” an element is an “open” expression, which merely means that a corresponding component or step exists, and should not be interpreted as excluding additional components or steps.

[0081] In order to achieve the purpose of the present invention, in some embodiments of a solid water-based MC modeling method and device, as Figure 1 As shown, the MC modeling method includes:

[0082] Step S1: Use a solid water measuring block to perform dose detection and record multiple sets of dose data;

[0083] Step S2: based on multiple sets of dose data, calculating the PDD curve and OAR curve of the linear accelerator;

[0084] Step S3: Based on the PDD curve and OAR curve, MC modeling is performed using the PSL model.

[0085] Further, when the PDD curve is measured, step S1 includes:

[0086] Step S1.1: assembling a number of solid water sub-blocks to form a solid water measurement block, such as stacking N-1 1 cm solid water sub-blocks or 2 0.2 cm solid water sub-blocks, one 2 cm solid water sub-block, and at least four 1 cm solid water sub-blocks to form a solid water measurement block;

[0087] Step S1.2: Place the solid water measuring block on the treatment bed and at the measuring position of the linear accelerator (align the vertical laser light with the vertical line on the solid water measuring block, and align the horizontal laser light with the upper surface of the solid water measuring block), and place the detector inside the solid water measuring block. The position of the detector is N cm downward from the upper surface of the solid water measuring block for quality control, which is the depth position of the detector.

[0088] Step S1.3: The linear accelerator starts detection, changes the field size to measure the dose value at the corresponding solid water thickness, and records multiple sets of PDD dose data.

[0089] In step S2, based on multiple groups of PDD dose data, the following formula (1) is used for fitting to obtain a PDD curve;

[0090]

[0091] Among them: k, n, μ are fitting parameters;

[0092] D is the thickness of the solid water measuring block.

[0093] For PDD, it is necessary to measure data from 0-30 cm. Because solid water of corresponding thickness needs to be covered above the ionization chamber when measuring data at different positions, the more data points are collected, the more operations need to be performed, which greatly affects the efficiency. The present invention uses formula (1) to fit the data, and by measuring a small number of data points, all data in the entire range of 0-30 cm can be obtained.

[0094] When measuring the OAR curve, step S1 is specifically as follows:

[0095] Step S1.1: assembling a number of solid water sub-blocks to form a solid water measurement block, such as stacking N-1 1 cm solid water sub-blocks or 2 0.2 cm solid water sub-blocks, one 2 cm solid water sub-block, and at least four 1 cm solid water sub-blocks to form a solid water measurement block;

[0096] Step S1.2: Place the solid water measuring block on the treatment bed and at the measuring position of the linear accelerator (align the vertical laser light with the vertical line on the solid water measuring block, and align the horizontal laser light with the upper surface of the solid water measuring block), and place the detector inside the solid water measuring block. The position of the detector is N cm downward from the upper surface of the solid water measuring block for quality control, which is the depth position of the detector.

[0097] Step S1.3: The linear accelerator starts detection, sets different field sizes, measures dose values ​​at different positions by moving the treatment bed, and records multiple sets of OAR dose data.

[0098] Further, step S3 includes the following contents:

[0099] The photon PSL is divided according to position and energy (m, n, e), where (m, n) marks the plane position perpendicular to the central axis of the beam and e refers to the energy;

[0100] The modeling problem can be described as solving equation (2);

[0101] Ax=b(2)

[0102] Among them, x is the weight of the PSL corresponding to each (m, n, e);

[0103] A is the PDD and OAR calculated in the solid water measurement block for each unit weight of PSL;

[0104] B is the PDD and OAR measured in the solid water measurement block;

[0105] Assuming that the beam is symmetric and smooth about the central axis, the following problem is obtained:

[0106]

[0107] in, is a function of radius r and energy e;

[0108] B is a linear algorithm, which is used to define the Expanded to two dimensions

[0109] and is the gradient operator;

[0110] The weight of the photon is obtained by solving (3);

[0111] For electrons, all electrons in the phase space file are considered as effective PSLs;

[0112] The effective PSL dose of unit weight in solid water is calculated in advance, and the measured dose is used to solve the effective PSL weight x using equation (4): e ;

[0113]

[0114] Among them, p e is the unit weighted effective PSL dose in the built-up area of ​​solid water;

[0115] p p is the dose calculated by the photon model obtained by equation (3);

[0116] p b is the measured dose;

[0117] <·|·> represents the inner product of vectors.

[0118] The present invention discloses a MC modeling based on phase-space-let (PSL). First, PSL is generated by splitting the phase space file, and weight factors related to these PSLs are further introduced. By making the PSL model correspond to any linear beam, the weight of each PSL is adjusted to take into account the difference between the unadjusted PSL and the expected beam. Once the weight is determined, in the subsequent MC dose calculation, each particle carries a weight factor related to the corresponding PSL.

[0119] Specifically, the dose of each unit weighted PSL in water is first calculated. Due to the linear superposition property of dose calculation, the dose of the weighted beam is the superposition of the PSL dose multiplied by the weight. The weight is obtained by comparing the calculated dose with the measured dose to minimize the difference. Only PDD and OAR are required for measuring dose, and no three-dimensional dose distribution is required.

[0120] This method has the advantages of being simple and universal. The weight coefficients of the PSL can be obtained by solving a simple quadratic optimization problem. By assuming that the particle directions of different accelerators are not much different, a universal PSL file can be used to model different accelerators of the same energy.

[0121] At present, the equipment for measuring PDD and OAR is a three-dimensional water tank. As a high-end quality control equipment, the water tank is expensive and the operation is cumbersome. At present, the quality control using the water tank requires the following steps. First, the water tank needs to be positioned; then water is poured into the water tank, the volume of the water tank is 675×645×560mm; after the measurement is completed, the water in the water tank needs to be pumped out. From the volume of the water tank, it can be seen that a large amount of water needs to be prepared for measurement, which affects the efficiency.

[0122] Due to the above disadvantages of the water tank, the use of water for modeling is also affected accordingly. Compared with the traditional use of a water tank to measure PDD and OAR, the present invention uses solid water as a carrier for measurement.

[0123] The present invention proposes a method for measuring the PDD and OAR of a linear accelerator by using solid water instead of a water tank. Solid water is a solid material that can simulate the absorption and scattering properties of water. Because it is easy to use, it has become a commonly used model material in radiotherapy quality control. Items that can be quality controlled with solid water include accelerator output dose measurement, dose repeatability, dose linearity, daily dose stability, etc. Compared with water tanks, solid water is low in cost, easy to obtain, and easy to store. It can achieve the functions of a water tank while avoiding the problems that exist in a water tank.

[0124] After measuring PDD and OAR using solid water, the measured PDD data are fitted, and all the data required for modeling can be obtained by measuring a small amount of data. The dose of each unit weight of PSL in solid water is calculated, and then the weight factor of PSL is determined using the measured dose and the calculated dose to achieve modeling of the MC model.

[0125] The embodiment of the present invention also discloses a solid water-based MC modeling device, comprising:

[0126] A dose data acquisition module is used to perform dose detection using a solid water measuring block and record multiple sets of dose data;

[0127] A curve calculation module, used to calculate the PDD curve and OAR curve of the linear accelerator based on multiple sets of dose data;

[0128] The MC modeling module is used to perform MC modeling using the PSL model based on the PDD curve and the OAR curve.

[0129] Furthermore, the dosage data acquisition module includes:

[0130] A splicing unit, used for assembling a plurality of solid water sub-blocks to form a solid water measuring block;

[0131] A placement unit is used to place the solid water measurement block on the treatment bed and at the measurement position of the linear accelerator, and to place the detector inside the solid water measurement block;

[0132] The detection unit is used to start the linear accelerator detection and record multiple sets of dose data.

[0133] Further, in step S2, based on multiple groups of dosage data, the following formula (1) is used for fitting to obtain a PDD curve;

[0134]

[0135] Among them: k, n, μ are fitting parameters;

[0136] D is the thickness of the solid water measuring block.

[0137] Furthermore, the MC modeling module is used to perform the following methods:

[0138] The photon PSL is divided according to position and energy (m, n, e), where (m, n) marks the plane position perpendicular to the central axis of the beam and e refers to the energy;

[0139] The modeling problem can be described as solving equation (2);

[0140] Ax=b(2)

[0141] Among them, x is the weight of the PSL corresponding to each (m, n, e);

[0142] A is the PDD and OAR calculated in the solid water measurement block for each unit weight of PSL;

[0143] B is the PDD and OAR measured in the solid water measurement block;

[0144] Assuming that the beam is symmetric and smooth about the central axis, the following problem is obtained:

[0145]

[0146]

[0147] in, is a function of radius r and energy e;

[0148] B is a linear algorithm, which is used to define the Expanded to two dimensions

[0149] and is the gradient operator;

[0150] The weight of the photon is obtained by solving (3);

[0151] For electrons, all electrons in the phase space file are considered as effective PSLs;

[0152] The effective PSL dose of unit weight in solid water is calculated in advance, and the measured dose is used to solve the effective PSL weight x using equation (4): e ;

[0153]

[0154] Among them, p e is the unit weighted effective PSL dose in the built-up area of ​​solid water;

[0155] p p is the dose calculated by the photon model obtained by equation (3);

[0156] p b is the measured dose;

[0157] <·|·> represents the inner product of vectors.

[0158] In this embodiment, the specific content of the MC modeling device based on solid water is similar to the content of the MC modeling method based on solid water disclosed in the above embodiment, and will not be repeated here.

[0159] The present invention discloses a MC modeling method and device based on solid water, which has the following beneficial effects:

[0160] First, solid water is used instead of a water tank to measure the PDD and OAR of the beam. Since solid water is low-cost, easy to obtain and easy to preserve, it can achieve the functions of a water tank while avoiding the problems that exist in the water tank, making accelerator modeling more convenient.

[0161] Second, a small amount of dose data is used for fitting to obtain the PDD curve, which can obtain all the data required for modeling, and is highly efficient.

[0162] Third, the present invention adopts the PSL model for MC modeling, and only PDD and OAR are needed to measure the dose, and no three-dimensional dose distribution is required. The method is simple and universal.

[0163] It should be understood that the various techniques described herein can be implemented in combination with hardware or software, or a combination thereof. Thus, the method and apparatus of the present invention, or some aspects or portions of the method and apparatus of the present invention, can take the form of program codes (i.e., instructions) embedded in a tangible medium, such as a floppy disk, a CD-ROM, a hard disk drive, or any other machine-readable storage medium, wherein when the program is loaded into a machine such as a computer and executed by the machine, the machine becomes a device for practicing the present invention.

[0164] The above shows and describes the basic principles and main features of the present invention and the advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions are only for illustrating the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, which shall fall within the scope of the present invention to be protected. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. The MC modeling method based on solid water is characterized by: include: Step S1: Use a solid water measuring block to perform dose detection and record multiple sets of dose data; Step S2: based on multiple sets of dose data, calculating the PDD curve and OAR curve of the linear accelerator; Step S3: Based on the PDD curve and OAR curve, MC modeling is performed using the PSL model.

2. The MC modeling method according to claim 1, characterized in that: The step S1 comprises: Step S1.1: assembling a number of solid water sub-blocks to form a solid water measurement block; Step S1.2: placing a solid water measuring block on the treatment bed and at the measuring position of the linear accelerator, and placing a detector inside the solid water measuring block; Step S1.3: The linear accelerator starts detection and records multiple sets of dose data.

3. The MC modeling method according to claim 1, characterized in that: In the step S2, based on multiple groups of dosage data, the following formula (1) is used for fitting to obtain a PDD curve; Among them: k, n, μ are fitting parameters; D is the thickness of the solid water measuring block.

4. The MC modeling method according to claim 1, characterized in that: The step S3 includes the following contents: The photon PSL is divided according to position and energy (m, n, e), where (m, n) marks the plane position perpendicular to the central axis of the beam and e refers to the energy; The modeling problem can be described as solving equation (2); Ax=b(2) Among them, x is the weight of the PSL corresponding to each (m, n, e); A is the PDD and OAR calculated in the solid water measurement block for each unit weight of PSL; B is the PDD and OAR measured in the solid water measurement block; Assuming that the beam is symmetric and smooth about the central axis, the following problem is obtained: in, is a function of radius r and energy e; B is a linear algorithm, which is used to define the Expanded to two dimensions and is the gradient operator; The weight of the photon is obtained by solving (3); For electrons, all electrons in the phase space file are considered as effective PSLs; The effective PSL dose of unit weight in solid water is calculated in advance, and the measured dose is used to solve the effective PSL weight x using equation (4): e ; Among them, p e is the unit weighted effective PSL dose in the built-up area of ​​solid water; p p is the dose calculated by the photon model obtained by equation (3); p b is the measured dose; <·|·> represents the inner product of vectors.

5. MC modeling equipment based on solid water, characterized in that, include: A dose data acquisition module is used to perform dose detection using a solid water measuring block and record multiple sets of dose data; A curve calculation module, used to calculate the PDD curve and OAR curve of the linear accelerator based on multiple sets of dose data; The MC modeling module is used to perform MC modeling using the PSL model based on the PDD curve and the OAR curve.

6. The MC modeling device according to claim 5, characterized in that: The dosage data acquisition module comprises: A splicing unit, used for assembling a plurality of solid water sub-blocks to form a solid water measuring block; A placement unit is used to place the solid water measurement block on the treatment bed and at the measurement position of the linear accelerator, and to place the detector inside the solid water measurement block; The detection unit is used to start the linear accelerator detection and record multiple sets of dose data.

7. The MC modeling device according to claim 5, characterized in that: In the step S2, based on multiple groups of dosage data, the following formula (1) is used for fitting to obtain a PDD curve; Among them: k, n, μ are fitting parameters; D is the thickness of the solid water measuring block.

8. The MC modeling device according to claim 5, characterized in that: The MC modeling module is used to perform the following methods: The photon PSL is divided according to position and energy (m, n, e), where (m, n) marks the plane position perpendicular to the central axis of the beam and e refers to the energy; The modeling problem can be described as solving equation (2); Ax=b(2) Among them, x is the weight of the PSL corresponding to each (m, n, e); A is the PDD and OAR calculated in the solid water measurement block for each unit weight of PSL; B is the PDD and OAR measured in the solid water measurement block; Assuming that the beam is symmetric and smooth about the central axis, the following problem is obtained: in, is a function of radius r and energy e; B is a linear algorithm, which is used to define the Expanded to two dimensions and is the gradient operator; The weight of the photon is obtained by solving (3); For electrons, all electrons in the phase space file are considered as effective PSLs; The effective PSL dose of unit weight in solid water is calculated in advance, and the measured dose is used to solve the effective PSL weight x using equation (4): e ; Among them, p e is the unit weighted effective PSL dose in the built-up area of ​​solid water; p p is the dose calculated by the photon model obtained by equation (3); p b is the measured dose; <·|·> represents the inner product of vectors.

Images