A method for synchronous verification of point dose and plane dose in CyberKnife radiotherapy planning

Abstract

The present invention relates to the technical field of radiotherapy dose verification, and specifically discloses a method for synchronous verification of point dose and plane dose of CyberKnife radiotherapy plan, comprising: constructing a CyberKnife patient dose verification device by a pinpoint ionization chamber, EBT3 film, solid water and a gold mark; using a simulated positioning CT scan verification device to obtain a verification device CT image; importing the verification device CT image into the CyberKnife patient treatment plan to generate a gold mark tracking phantom plan; registering the CT image of the patient radiotherapy plan with the CT image corresponding to the phantom plan, and transplanting the beam information in the patient radiotherapy plan to the phantom plan; using a high-resolution beam tracking algorithm to recalculate the dose distribution of the treatment beam on the phantom plan image; recording the median dose of the sensitive volume of the ionization chamber, and exporting the dose distribution map of the layer where the film plane is located in the phantom plan to perform absolute point dose analysis and plane dose analysis. The present invention can improve the error detection rate of patient plan verification.

Description

Technical Field

[0001] The present invention relates to the technical field of radiotherapy dose verification, and more specifically, to a method for synchronously verifying a point dose and a plane dose of a CyberKnife radiotherapy plan. Background Art

[0002] As a special device for stereotactic radiotherapy, CyberKnife is increasingly used in the treatment of whole-body tumors in modern radiotherapy. CyberKnife uses non-coplanar and non-isocentric beam irradiation to achieve a rapid drop in the dose outside the tumor target area, forming a distribution pattern of high dose inside the tumor and low dose outside the tumor. This pattern can not only better improve the tumor control rate, but also better protect the endangered organs. However, compared with conventional linear accelerator radiotherapy beams, the irradiation method of stereotactic radiotherapy based on CyberKnife non-isocentric and non-coplanar beams is more complicated. Complex radiotherapy plans will inevitably lead to deviations between the dose distribution calculated in the treatment planning system (TPS) and the dose distribution during the actual execution of the plan. As the complexity of the treatment plan increases, the uncertainty of dose calculation and plan execution will continue to increase. In order to ensure the safety and reliability of the execution of CyberKnife radiotherapy plans, it is required to verify the dose of the patient's radiotherapy plan before the treatment plan is executed. The quality of the dose verification results is crucial to the patient's treatment effect, so it is an indispensable part of the quality control link.

[0003] At present, the conventional method for verifying CyberKnife radiotherapy plans is to determine whether the plan meets clinical treatment needs by detecting the absolute point dose in the ionization chamber. Absolute dose verification focuses on the accuracy of the overall dose, but cannot reflect the dose distribution in the entire treatment area. If the dose distribution shape is deviated, or even the tissue outside the target area is over-irradiated or the dose coverage is insufficient, the point dose verification will not be able to identify it, so the verification result is one-sided. Conventional linear accelerators can verify the plane dose based on a two-dimensional matrix ionization chamber or a semiconductor matrix. However, these devices can only be used to detect isocentric coplanar beams, so it is impossible to verify the plane dose of CyberKnife. In addition, CyberKnife stereotactic radiotherapy plans mostly use small fields for irradiation, and detection requires a high-resolution detector for accurate measurement. Commercial electronic detection equipment has no way to accurately verify the treatment plan for small lesions due to process limitations. Therefore, how to improve the verification of the absolute point dose and small field plane dose of CyberKnife plans is of great significance to the safety and effectiveness of cancer patient treatment. Summary of the invention

[0004] The present invention provides a method for synchronously verifying point dose and plane dose of CyberKnife radiotherapy plan, which solves the problems of one-sidedness and insufficient accuracy of existing CyberKnife patient radiotherapy plan dose verification, improves the error detection rate of patient plan verification, reduces radiotherapy risks, and avoids clinical risks of insufficient target area dose or excessive irradiation of endangered organs due to insufficient verification.

[0005] To achieve the above objectives, the present invention provides the following technical solutions:

[0006] A method for synchronously verifying point dose and plane dose of CyberKnife radiotherapy plan, comprising:

[0007] The CyberKnife patient dose verification device is constructed from pinpoint ionization chamber, EBT3 film, solid water and gold standard;

[0008] Use simulated positioning CT scanning to verify the device to obtain CT images for verification of the device;

[0009] Importing the verification device CT image into the CyberKnife patient treatment plan, generating a phantom plan for gold standard tracking, and generating a patient dose verification plan based on the phantom plan;

[0010] Registering the CT image of the patient's radiotherapy plan with the CT image corresponding to the phantom plan, and transplanting the beam information in the patient's radiotherapy plan to the phantom plan;

[0011] A high-resolution beam tracking algorithm is used to recalculate the dose distribution of the treatment beam on the phantom planning images;

[0012] The median dose of the sensitive volume of the ionization chamber is recorded, and the dose distribution map of the layer where the film plane in the phantom plan is located is exported to perform absolute point dose analysis and plane dose analysis, thereby verifying whether the patient's radiotherapy plan is suitable for patient treatment.

[0013] Preferably, it also includes:

[0014] The accuracy of the dose output of the radiotherapy equipment is verified by measuring the two-dimensional dose distribution of the patient's radiotherapy plan at the effective measurement point in the ionization chamber and on the film plane and comparing it with the measured values ​​of the actual patient's radiotherapy plan.

[0015] Preferably, the construction of CyberKnife patient dose verification equipment includes:

[0016] The solid water is composed of 11 PTW RW3 water equivalent solid water stacks, each with a size of 30cm x 30cm x 1cm. A hole is drilled in the center of the sixth solid water in the middle in the horizontal direction, and the top of the hole is located exactly at the center of mass of the solid water, which is used to insert the pinpoint ionization chamber for point dose measurement;

[0017] The EBT3 film is placed at the bottom of the fifth solid water block to perform planar dose measurement, and the effective measurement point of the ionization chamber is 0.5 cm away from the EBT3 film;

[0018] Four non-coplanar gold labels were set in the 11 pieces of solid water, and the size of the gold labels was 2.7 x 1.2 x 0.6 mm.

[0019] Preferably, the construction of the CyberKnife patient dose verification device further includes:

[0020] According to the dose response characteristics of EBT3 film, a dose-grayscale curve is created through the film scale to convert the grayscale information of film development into absorbed dose, which is used to verify the dose accuracy of the patient's radiotherapy plan.

[0021] Preferably, the step of creating a dose and grayscale curve by film scale comprises:

[0022] Prepare the film and cut it into a size of 5 cm × 5 cm according to the experimental requirements;

[0023] Mark the number, irradiation dose and placement direction on each film;

[0024] According to the dose range actually used in clinical practice, different dose gradients are selected for irradiation. The dose gradients are 0.1Gy, 0.25Gy, 0.5Gy, 1Gy, 2Gy, 4Gy, 6Gy, 8Gy, and 10Gy. Each film corresponds to a different dose.

[0025] Scan radiation film to obtain 24-color true color images of the film;

[0026] Preprocess the film image to remove background noise and complete non-uniformity correction;

[0027] The dose and grayscale curves were obtained using a polynomial fitting algorithm.

[0028] Preferably, the absolute point dose analysis comprises:

[0029] After the patient dose verification plan is executed, the dosimeter readings are obtained and corrected for temperature and air pressure to the actual measurement results of the absolute point dose;

[0030] Compare the deviation between the median dose of the effective measurement point of the ionization chamber in the patient dose verification plan and the actual measurement result;

[0031] If the deviation value is less than the set threshold, it means that the consistency of the beam parameters and dose output of the CyberKnife in executing the patient's radiotherapy plan has been verified. Otherwise, the patient's radiotherapy plan cannot be used for patient treatment.

[0032] Preferably, the planar dose analysis includes:

[0033] Import the film-level dose distribution map derived from the patient dose verification plan, the blank film of the same production batch, and the scanned image of the film after irradiation into the film analysis software;

[0034] Use blank film to perform background denoising on the test film;

[0035] Retrieve the film dose-grayscale correction file to convert the verification film from grayscale image to dose image;

[0036] Perform image registration between the film-level dose distribution map derived from the patient dose verification plan and the film dose image;

[0037] Gamma analysis method was used to analyze the dose and position consistency of the registered images;

[0038] If the Gamma pass rate is ≥90%, it means that the results of the patient's radiotherapy plan executed by CyberKnife are consistent with the calculation results of the treatment planning system, and the treatment plan meets the preset requirements, otherwise the treatment plan will not be executed.

[0039] Preferably, it also includes:

[0040] Before executing the patient dose verification plan, the verification equipment is positioned and preheated, the absolute point dose detection device is preheated to remove the measurement interference signal, and after the EBT3 film for patient dose plan verification is placed in solid water, the verification equipment is placed at the center of image registration;

[0041] The patient verification plan is retrieved, and the fine positioning is further completed based on the gold standard in solid water, so that the positioning error satisfies the translation direction deviation ≤±0.2mm and the angle rotation deviation ≤±0.2°. The CyberKnife beam is emitted to execute the patient verification plan and the output of the absolute dose is measured;

[0042] After the patient verification plan is completed, wait 24 hours and scan the radiation film.

[0043] Preferably, preheating the verification device includes:

[0044] When preheating the verification equipment, connect the ionization chamber to the dosimeter. After turning on the dose, the CyberKnife aims at the effective measurement area of ​​the ionization chamber to emit a beam of 100MU, preheat the hot dose measurement equipment and remove background noise and dark current signals, reducing measurement disturbance factors.

[0045] Preferably, positioning the verification device includes:

[0046] Place the verification device horizontally on the CyberKnife treatment bed, turn on the positioning laser light, and adjust the position of the solid water so that the center line of the solid water coincides with the positioning laser light line to ensure that the solid water can be placed at the center of the image registration during the initial positioning.

[0047] The present invention provides a method for synchronously verifying point dose and plane dose of a CyberKnife radiotherapy plan. A CyberKnife patient dose verification device is constructed by a pinpoint ionization chamber, an EBT3 film, solid water and a gold standard. The CyberKnife patient treatment plan is verified by the verification device. The ionization chamber and the EBT3 film are used for synchronous verification, so that the absolute accuracy of the point dose verification is combined with the relative verification of the plane dose distribution. The method is adapted to the complex non-coplanar small field treatment characteristics of the CyberKnife, makes up for the limitation of a single verification method, solves the problems of one-sidedness and insufficient accuracy of the existing CyberKnife patient radiotherapy plan dose verification, improves the error detection rate of the patient plan verification, reduces the risk of radiotherapy, and avoids the clinical risk of insufficient target area dose or excessive irradiation of endangered organs due to insufficient verification. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] In order to more clearly illustrate the specific embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below.

[0049] Figure 1 It is a schematic diagram of a method for synchronously verifying a CyberKnife radiotherapy plan point dose and a plane dose provided by the present invention.

[0050] Figure 2 It is a schematic diagram of a CyberKnife patient dose verification device provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0051] In order to enable persons skilled in the art to better understand the solutions of the embodiments of the present invention, the embodiments of the present invention are further described in detail below in conjunction with the accompanying drawings and implementation modes.

[0052] In view of the problem that the current CyberKnife patient radiotherapy plan dose adopts a single verification method, which has the problems of one-sidedness and insufficient accuracy, the present invention provides a method for synchronously verifying the point dose and plane dose of a CyberKnife radiotherapy plan, which solves the problems of one-sidedness and insufficient accuracy in the existing CyberKnife patient radiotherapy plan dose verification, can improve the error detection rate of patient plan verification, reduce radiotherapy risks, and avoid clinical risks of insufficient target area dose or excessive irradiation of endangered organs due to insufficient verification.

[0053] like Figure 1 As shown, a method for synchronously verifying point dose and plane dose of CyberKnife radiotherapy plan includes:

[0054] S1: A CyberKnife patient dose verification device was constructed using a pinpoint ionization chamber, EBT3 film, solid water, and a gold standard.

[0055] S2: Use a simulated positioning CT scan to verify the device to obtain a CT image of the verification device.

[0056] S3: Import the verification device CT image into the CyberKnife patient treatment plan, generate a phantom plan for gold standard tracking, and generate a patient dose verification plan based on the phantom plan.

[0057] S4: registering the CT image of the patient's radiotherapy plan with the CT image corresponding to the phantom plan, and transplanting the beam information in the patient's radiotherapy plan to the phantom plan.

[0058] S5: Recalculate the dose distribution of the treatment beam on the phantom planning image using a high-resolution beam tracking algorithm.

[0059] S6: Record the median dose of the sensitive volume of the ionization chamber, and export the dose distribution map of the layer where the film plane in the phantom plan is located to perform absolute point dose analysis and plane dose analysis, thereby verifying whether the patient's radiotherapy plan is suitable for the patient's treatment.

[0060] Specifically, for the selection of verification equipment, the detection of absolute point dose requires the use of an ionization chamber detector with the smallest possible sensitive volume to adapt to the small field high dose gradient area of ​​the CyberKnife high-precision radiotherapy equipment, and a pinpoint ionization chamber is generally used. For two-dimensional plane dose detection equipment, first of all, the detector is required to be able to perform non-coplanar and non-isocentric beam detection, without angle dependence, and to achieve complete dose response for beams irradiated at any angle. Secondly, the resolution of the detector should be high to meet the requirements of small field dose measurement. Finally, the detector mass density needs to meet the water equivalent characteristics to achieve accurate delivery and verification of doses in radiotherapy. Therefore, it is most rational to select EBT3 film through research and testing. As a self-developing film, EBT3 film does not require fixing and developing operations, and is more convenient to use. In addition, the film has good water equivalence, high resolution, independent energy response, excellent dose response linearity, and no beam angle dependence, so it is very suitable for CyberKnife two-dimensional plane dose verification.

[0061] Patient dose verification plan creation: Place the verification device on the simulated positioning CT treatment bed. Set the tube exposure parameters; tube voltage 120kV, photocurrent 320mA, scanning layer thickness 1mm, and perform CT scanning. Use the CyberKnife data management system to import the verification device CT image into the CyberKnife planning system.

[0062] Patient dose verification plan generation: First, load the verification device CT image, generate the gold standard tracking phantom plan, and then regenerate the dose verification plan based on the phantom plan. The dose verification plan is established in three steps. The first step is to align the CT image of the patient treatment plan with the CT image of the verification device. Since the absolute point dose of the verification plan should be measured in the high-dose area of ​​the target area. Therefore, image registration requires that the high-dose flat area in the target area in the patient treatment plan image should be aligned with the effective measurement area (sensitive volume) of the ionization chamber in the phantom plan image. The effective measurement area of ​​the ionization chamber is located in the uniform dose area of ​​the treatment plan target area, and ideally the maximum dose gradient is less than 3%. The second step is to transfer the information of the beam in the treatment plan, such as the robot control node coordinates, target coordinates, collimator size, monitoring unit, etc., to the phantom plan. The third step is to recalculate the dose distribution of the treatment beam on the phantom plan image using a high-resolution beam tracking algorithm. Finally, the median dose of the sensitive volume of the ionization chamber is recorded, and the DICM dose file of the layer where the film plane in the verification plan is located is exported.

[0063] This method uses absolute point dose analysis and plane dose analysis to determine whether the patient's radiotherapy plan is suitable for the patient's treatment. The method uses ionization chamber and EBT3 film for synchronous verification, combining the absolute accuracy of point dose verification with the relative verification of plane dose distribution, adapting to the complex non-coplanar small field treatment characteristics of CyberKnife, making up for the limitations of a single verification method, improving the error detection rate of patient plan verification, and reducing the risk of radiotherapy.

[0064] Furthermore, the method also includes: measuring the two-dimensional dose distribution of the patient's radiotherapy plan at the effective measurement point in the ionization chamber and on the film plane, and comparing and verifying it with the measured values ​​of the actual patient's radiotherapy plan to verify whether the dose output of the radiotherapy equipment is accurate.

[0065] Specifically, the principle of patient plan dose verification is to measure the two-dimensional dose distribution of the patient's radiotherapy plan at the effective measurement point in the ionization chamber and on the film plane, and compare it with the dose calculated by the treatment planning system (TPS) to verify whether the dose output of the radiotherapy equipment is accurate and ensure that the treatment plan can achieve the expected dose distribution in the patient's body. Therefore, dose verification mainly compares the calculated values ​​of the verification plan generated by TPS (point dose in the ionization chamber and two-dimensional dose distribution on the film plane) with the measured values ​​of the actual plan execution.

[0066] like Figure 2 As shown, further, the construction of the CyberKnife patient dose verification device includes:

[0067] The solid water 3 is composed of 11 PTW RW3 water equivalent solid water stacks, each with a size of 30cm x 30cm x 1cm. A hole is drilled horizontally in the center of the sixth solid water block, and the top of the hole is located exactly at the center of mass of the solid water for inserting the pinpoint ionization chamber 1 for point dose measurement.

[0068] The EBT3 film 2 is placed at the bottom of the fifth block of solid water for planar dose measurement, and the effective measurement point of the ionization chamber is spaced 0.5 cm from the EBT3 film 2.

[0069] Four non-coplanar gold labels 4 are set in the 11 pieces of solid water, and the size of the gold labels is: 2.7x1.2x0.6mm.

[0070] Specifically, the selection of solid water must meet water equivalence, physical stability, multi-energy response, and compatibility with the detector. Selecting the appropriate solid water material according to these standards can ensure the accuracy of the dose verification results and improve the quality control level of radiotherapy. Based on the above requirements, 11 pieces of PTW RW3 water-equivalent solid water are used, each with a size of 30cm x 30cm x 1cm and a physical density of 1.04g / cm 3 . A hole is drilled horizontally in the center of the sixth solid water block in the middle, and the top of the hole is located exactly at the center of mass of the solid water, which is used to insert the PinPoint ionization chamber for point dose measurement. The shape of the hole matches the ionization chamber. Four high-density metal markers (gold labels) are implanted in the solid water, with a size of 2.7x1.2x0.6mm. The arrangement of the four gold labels needs to meet the following requirements: the distance between any two gold labels is greater than 2cm; the angle between any three gold labels is ≥1.5°; the X-ray is projected along the 45° direction on the phantom, and the gold labels in the phantom cannot be coplanar in the image.

[0071] The verification equipment consists of three parts: pinpoint ionization chamber, EBT3 film and solid water. As shown in the figure, there are 11 layers of solid water, with four non-coplanar gold labels. The ionization chamber is placed in the middle hole of the solid water layer, and the top of the ionization chamber is required to fit tightly in the hole to ensure the repeatability and stability of the ionization chamber position. There is 6.5 cm of built-up solid water above the effective measurement point of the ionization chamber, and 6.5 cm of back-scattered solid water below. The EBT3 film is placed at the bottom of the fifth piece of solid water, with 5 cm of built-up solid water above the film and 7 cm of built-up solid water below. The effective measurement point of the ionization chamber is 0.5 cm away from the film. In order to ensure the verification of a small target area, the ionization chamber and the film can simultaneously verify the dose accuracy of the high-dose area of ​​the target area.

[0072] Furthermore, the construction of the CyberKnife patient dose verification device also includes:

[0073] According to the dose response characteristics of EBT3 film, a dose-grayscale curve is created through the film scale to convert the grayscale information of film development into absorbed dose, which is used to verify the dose accuracy of the patient's radiotherapy plan.

[0074] Specifically, the principle of using film for dose verification is based on the dose response characteristics of radiation-sensitive film. By analyzing the correspondence between the optical density change of the film after radiation exposure (the grayscale of film development) and the absorbed dose, the quantitative measurement and distribution verification of the dose can be achieved. The film scale is to create a dose-grayscale curve, through which the grayscale information of film development can be converted into absorbed dose.

[0075] Further, the step of creating a dose and grayscale curve by using a film scale includes:

[0076] Prepare the film and cut it into a size of 5 cm × 5 cm according to the experimental requirements.

[0077] Mark each film with the number, radiation dose and placement direction.

[0078] According to the dose range actually used in clinical practice, different dose gradients are selected for irradiation. The dose gradients are 0.1Gy, 0.25Gy, 0.5Gy, 1Gy, 2Gy, 4Gy, 6Gy, 8Gy, and 10Gy, and each film corresponds to a different dose.

[0079] Scan the radiation film to obtain the film's 24-color true color image.

[0080] Film images are preprocessed to remove background noise and perform non-uniformity correction.

[0081] The dose and grayscale curves were obtained using a polynomial fitting algorithm.

[0082] In one embodiment, to generate the curve, the tool PTW RW solid water, size 30cmx30cmx1cm, EBT3 self-developing film, pinpoint ionization chamber PTW TW31016, sensitive volume 0.4cc, measurement conditions SAD=80cm, solid water built-up thickness of 3cm, backscatter thickness of 6cm are required.

[0083] The EBT3 film graduation process is as follows:

[0084] 1. Preparation of film:

[0085] (1) Film cutting: According to experimental requirements, cut the EBT3 film into 5 cm × 5 cm size, a total of 10 sheets.

[0086] (2) Film identification: Mark the number, irradiation dose and placement direction on each film to ensure that the direction and dose of each film can be correctly identified during subsequent processing and analysis.

[0087] 2. Irradiated film:

[0088] (1) Setting irradiation conditions: According to the dose range actually used in clinical practice, different dose gradients are selected for irradiation. The dose gradients are 0.1Gy, 0.25Gy, 0.5Gy, 1Gy, 2Gy, 4Gy, 6Gy, 8Gy, and 10Gy, and each film uses a different dose.

[0089] (2) Irradiated film: 10 films are irradiated on the accelerator according to the marked dose. In order to ensure the accuracy and uniformity of the dose, the 10 films are placed in the water equivalent phantom and placed in the same direction, with a layer thickness of 3 cm and a backscatter thickness of 5 cm, and irradiated with the corresponding dose. After irradiation, the film will develop different grayscales (different films will display different grayscales due to different irradiation doses, and the higher the dose, the darker the color).

[0090] (3) Irradiation record: Record the beam energy and irradiation time of each film in detail, and then store it away from light.

[0091] 3. Scan film:

[0092] BET3 film has a time-dependent response to dose deposition. In order to ensure the stability of the film dose response, the film is generally required to be irradiated for 24 hours before scanning. It is recommended to use a high-resolution scanner (such as Epson PerfectionV700 / V800) for scanning, with the resolution set to 96 dpi, and a 24-color true color transmission scanning mode to ensure sufficient resolution and grayscale to reflect the changes in dose distribution. The image is not color corrected to avoid image distortion. Before scanning the film, check whether there are scratches, fingerprints, dust and other stains on the film surface to avoid introducing interference factors when scanning the image, reducing the image quality and authenticity. It should be noted that all films need to be placed in the same direction during scanning to ensure that the development of the film's photosensitive crystals is not affected by the uneven light source of the scanner.

[0093] 4. Film image processing:

[0094] Use image processing software (such as ImageJ or MATLAB) to remove image background noise and perform non-uniformity calibration to improve the consistency of film dose response.

[0095] 5. Create dose-grayscale correction file:

[0096] Use film analysis software (such as Film QA or RIT113, etc.) to establish a dose-grayscale curve: Draw a dose-grayscale curve based on the known gradient dose and the corresponding film grayscale value. Usually, a polynomial fitting method is used to obtain a higher fitting accuracy, thereby establishing a dose-grayscale calibration curve. This curve can be used to convert the grayscale value of an unknown dose film into an actual dose to verify the dose accuracy of the radiotherapy plan.

[0097] Further, the absolute point dose analysis includes:

[0098] After the patient dose verification plan is executed, the dosimeter readings are obtained and corrected for temperature and air pressure to the actual measurement results of the absolute point dose;

[0099] Compare the deviation between the median dose of the effective measurement point of the ionization chamber in the patient dose verification plan and the actual measurement result;

[0100] If the deviation value is less than the set threshold, it means that the consistency of the beam parameters and dose output of the CyberKnife in executing the patient's radiotherapy plan has been verified. Otherwise, the patient's radiotherapy plan cannot be used for patient treatment.

[0101] Specifically, after the patient verification plan is executed, the dosimeter readings obtained are corrected for temperature and air pressure to the actual measurement results of the absolute point dose. Compare the deviation between the median dose (calculated value) of the effective measurement point of the ionization chamber in the patient verification plan and the actual measurement result (measured value), as shown below: △ = (measured value - calculated value) / calculated value x 100%, with a requirement of △ ≤ 3%. If the deviation is less than 3%, it means that the consistency of the beam parameters and dose output of the CyberKnife in executing the treatment plan has been verified. Otherwise, the plan cannot be used for patient treatment, and further investigation is required to determine whether there are risks in the treatment plan and treatment equipment.

[0102] Further, the planar dose analysis includes:

[0103] Import the film-level dose distribution map derived from the patient dose verification plan, the blank film of the same production batch, and the scanned image of the film after irradiation into the film analysis software;

[0104] Use blank film to perform background denoising on the test film;

[0105] Retrieve the film dose-grayscale correction file to convert the verification film from grayscale image to dose image;

[0106] Perform image registration between the film-level dose distribution map derived from the patient dose verification plan and the film dose image;

[0107] Gamma analysis method was used to analyze the dose and position consistency of the registered images;

[0108] If the Gamma pass rate is ≥90%, it means that the results of the patient's radiotherapy plan executed by CyberKnife are consistent with the calculation results of the treatment planning system, and the treatment plan meets the preset requirements, otherwise the treatment plan will not be executed.

[0109] In one embodiment, the planar two-dimensional dose analysis, the specific analysis process is as follows:

[0110] (1) Import the film-level dose distribution map derived from the patient verification plan, the blank film of the same production batch, and the scanned image of the irradiated film into the film analysis software. Use the blank film to perform background denoising on the test film.

[0111] (2) Retrieve the film dose-grayscale correction file and convert the verification film from a grayscale image to a dose image.

[0112] (3) Perform image registration between the film-level dose distribution map derived from the verification plan and the film dose image.

[0113] (4) Gamma analysis method was used to analyze the dose and position consistency of the registered images. The gamma analysis parameters were selected as grayscale threshold 30%, dose deviation 2%, and distance deviation 2 mm, and the gamma pass rate was analyzed by software.

[0114] (5) Evaluation criteria: The Gamma pass rate is required to be ≥ 90%. If the pass rate is greater than 90%, it means that the results of the plan executed by CyberKnife are highly consistent with the TPS plan calculation results in terms of equipment mechanical accuracy, image guidance system, and relative dose output accuracy, and the plan can be used to treat patients. Otherwise, the difference is large, the treatment plan should not be executed, and multiple inspections are required to check and correct the problems.

[0115] The method further includes:

[0116] Before executing the patient dose verification plan, the verification equipment is positioned and preheated, and the absolute point dose detection device is preheated to remove the measurement interference signal. After the EBT3 film used for patient dose plan verification is placed in solid water, the verification equipment is placed at the center of the image registration.

[0117] The patient verification plan is retrieved, and the fine positioning is further completed based on the gold standard in solid water, so that the positioning error satisfies the translation direction deviation ≤±0.2mm and the angular rotation deviation ≤±0.2°. The CyberKnife beam is emitted to execute the patient verification plan and perform output measurement of the absolute dose.

[0118] After the patient verification plan is completed, wait 24 hours and scan the radiation film.

[0119] In one embodiment, the X-ray tube filming parameters are set as follows: tube voltage 120Kv, tube current 100mA, exposure time 100ms. X-ray orthogonal images are taken, and the verification plan image is registered with the real-time tracking image based on the gold standard implanted in solid water to obtain the positioning error. The positioning error is corrected by moving the treatment bed. When the positioning error satisfies the translation direction deviation ≤±0.2mm and the angle rotation deviation ≤±0.2°, the beam can be emitted to execute the verification plan. At the same time, the dosimeter measures the dose output of the verification plan beam by beam, and records the ionization chamber reading at the end of the plan.

[0120] When scanning the EBT3 verification film, the irradiated film should be kept away from light after being taken out of the phantom, and scanned 24 hours after the film is irradiated. The film scanning conditions are required to be consistent with the film scale. The film placement direction is consistent with the scanner scanning direction; the film scanning parameters are resolution 96bpi, 24 true colors, and no color correction. Image processing is performed through image software to remove noise and reduce image non-uniformity.

[0121] Furthermore, the verification equipment is preheated, including:

[0122] When preheating the verification equipment, connect the ionization chamber to the dosimeter. After turning on the dose, the CyberKnife aims at the effective measurement area of ​​the ionization chamber to emit a beam of 100MU, preheat the hot dose measurement equipment and remove background noise and dark current signals, reducing measurement disturbance factors.

[0123] Furthermore, the verification equipment is positioned, including:

[0124] Place the verification device horizontally on the CyberKnife treatment bed, turn on the positioning laser light, and adjust the position of the solid water so that the center line of the solid water coincides with the positioning laser light line to ensure that the solid water can be placed at the center of the image registration during the initial positioning.

[0125] It can be seen that the present invention provides a method for synchronously verifying the point dose and plane dose of a CyberKnife radiotherapy plan. A CyberKnife patient dose verification device is constructed by a pinpoint ionization chamber, an EBT3 film, solid water and a gold standard. The CyberKnife patient treatment plan is verified by the verification device. The ionization chamber and the EBT3 film are used for synchronous verification, so that the absolute accuracy of the point dose verification is combined with the relative verification of the plane dose distribution, which adapts to the complex non-coplanar small field treatment characteristics of the CyberKnife, makes up for the limitations of a single verification method, solves the problems of one-sidedness and insufficient accuracy of the existing CyberKnife patient radiotherapy plan dose verification, can improve the error detection rate of patient plan verification, reduce the risk of radiotherapy, and avoid the clinical risk of insufficient target dose or excessive irradiation of endangered organs due to insufficient verification.

[0126] The above describes in detail the structure, features and effects of the present invention based on the embodiments shown in the drawings. The above is only a preferred embodiment of the present invention, but the present invention is not limited to the scope of implementation shown in the drawings. Any changes made in accordance with the concept of the present invention, or modifications to equivalent embodiments with equivalent changes, which still do not exceed the spirit covered by the description and drawings, should be within the protection scope of the present invention.

Claims

1. A method for synchronous verification of point dose and plane dose of CyberKnife radiotherapy plan, characterized in that: include: The CyberKnife patient dose verification device is constructed from pinpoint ionization chamber, EBT3 film, solid water and gold standard; Use simulated positioning CT scanning to verify the device to obtain CT images for verification of the device; Importing the verification device CT image into the CyberKnife patient treatment plan, generating a phantom plan for gold standard tracking, and generating a patient dose verification plan based on the phantom plan; Registering the CT image of the patient's radiotherapy plan with the CT image corresponding to the phantom plan, and transplanting the beam information in the patient's radiotherapy plan to the phantom plan; A high-resolution beam tracking algorithm is used to recalculate the dose distribution of the treatment beam on the phantom planning images; Recording the median dose of the sensitive volume of the ionization chamber, and exporting the dose distribution map of the layer where the film plane in the phantom plan is located, so as to perform absolute point dose analysis and plane dose analysis, and further verify whether the patient's radiotherapy plan is suitable for the patient's treatment; By measuring the two-dimensional dose distribution of the patient's radiotherapy plan at the effective measurement point in the ionization chamber and on the film plane, the dose distribution is compared with the measured values ​​of the actual patient's radiotherapy plan to verify whether the dose output of the radiotherapy equipment is accurate; The CyberKnife patient dose verification device is constructed, comprising: The solid water is composed of 11 PTW RW3 water equivalent solid water stacks, each with a size of 30cm x 30cm x 1cm. A hole is drilled in the center of the sixth solid water in the middle in the horizontal direction, and the top of the hole is located exactly at the center of mass of the solid water, which is used to insert the pinpoint ionization chamber for point dose measurement; The EBT3 film is placed at the bottom of the fifth solid water block to perform planar dose measurement, and the effective measurement point of the ionization chamber is 0.5 cm away from the EBT3 film; Four non-coplanar gold labels were set in the 11 pieces of solid water, and the size of the gold labels was 2.7 x 1.2 x 0.6 mm.

2. The method for synchronous verification of point dose and plane dose of CyberKnife radiotherapy plan according to claim 1, characterized in that: The CyberKnife patient dose verification device is constructed, and further comprises: According to the dose response characteristics of EBT3 film, a dose-grayscale curve is created through the film scale to convert the grayscale information of film development into absorbed dose, which is used to verify the dose accuracy of the patient's radiotherapy plan.

3. The method for synchronous verification of point dose and plane dose of CyberKnife radiotherapy plan according to claim 2, characterized in that: The step of creating a dose and grayscale curve by film gradation includes: Prepare the film and cut it into a size of 5 cm × 5 cm according to the experimental requirements; Mark the number, irradiation dose and placement direction on each film; According to the dose range actually used in clinical practice, different dose gradients are selected for irradiation. The dose gradients are 0.1Gy, 0.25Gy, 0.5Gy, 1Gy, 2Gy, 4Gy, 6Gy, 8Gy, and 10Gy. Each film corresponds to a different dose. Scan radiation film to obtain 24-color true color images of the film; Preprocess the film image to remove background noise and complete non-uniformity correction; The dose and grayscale curves were obtained using a polynomial fitting algorithm.

4. The method for synchronous verification of point dose and plane dose of CyberKnife radiotherapy plan according to claim 3, characterized in that: The absolute point dose analysis includes: After the patient dose verification plan is executed, the dosimeter readings are obtained and corrected for temperature and air pressure to the actual measurement results of the absolute point dose; Compare the deviation between the median dose of the effective measurement point of the ionization chamber in the patient dose verification plan and the actual measurement result; If the deviation value is less than the set threshold, it means that the consistency of the beam parameters and dose output of the CyberKnife in executing the patient's radiotherapy plan has been verified. Otherwise, the patient's radiotherapy plan cannot be used for patient treatment.

5. The method for synchronous verification of point dose and plane dose of CyberKnife radiotherapy plan according to claim 4, characterized in that: The planar dose analysis includes: Import the film-level dose distribution map derived from the patient dose verification plan, the blank film of the same production batch, and the scanned image of the film after irradiation into the film analysis software; Use blank film to perform background denoising on the test film; Retrieve the film dose-grayscale correction file to convert the verification film from grayscale image to dose image; Perform image registration between the film-level dose distribution map derived from the patient dose verification plan and the film dose image; Gamma analysis method was used to analyze the dose and position consistency of the registered images; If the Gamma pass rate is ≥90%, it means that the results of the patient's radiotherapy plan executed by CyberKnife are consistent with the calculation results of the treatment planning system, and the treatment plan meets the preset requirements, otherwise the treatment plan will not be executed.

6. The method for synchronous verification of point dose and plane dose of CyberKnife radiotherapy plan according to claim 5, characterized in that: Also includes: Before executing the patient dose verification plan, the verification equipment is positioned and preheated, the absolute point dose detection device is preheated to remove the measurement interference signal, and after the EBT3 film for patient dose plan verification is placed in solid water, the verification equipment is placed at the center of image registration; The patient verification plan is retrieved, and the fine positioning is further completed based on the gold standard in solid water, so that the positioning error satisfies the translation direction deviation ≤±0.2mm and the angle rotation deviation ≤±0.2°. The CyberKnife beam is emitted to execute the patient verification plan and the output of the absolute dose is measured; After the patient verification plan is completed, wait 24 hours and scan the radiation film.

7. The method for synchronous verification of point dose and plane dose of CyberKnife radiotherapy plan according to claim 6, characterized in that: Preheat the verification equipment, including: When preheating the verification equipment, connect the ionization chamber to the dosimeter. After turning on the dose, the CyberKnife aims at the effective measurement area of ​​the ionization chamber to emit a beam of 100MU, preheat the hot dose measurement equipment and remove background noise and dark current signals, reducing measurement disturbance factors.

8. The method for synchronous verification of point dose and plane dose of CyberKnife radiotherapy plan according to claim 7, characterized in that: Position the verification equipment, including: Place the verification device horizontally on the CyberKnife treatment bed, turn on the positioning laser light, and adjust the position of the solid water so that the center line of the solid water coincides with the positioning laser light line to ensure that the solid water can be placed at the center of the image registration during the initial positioning.

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