Method for measuring intraoperative radiotherapy Intrabeam water absorbed dose based on air kerma

Abstract

The invention discloses a method for measuring intraoperative radiotherapy Intrabeam water absorbed dose based on air kerma. The method comprises the following steps: characterizing a spectrum; a radiation substance matched with or close to the spectrum is selected, and the energy spectrum of the radiation substance is represented; acquiring measurement parameters of the air kerma rate; calculating a first correction factor by adopting a Monte Carlo method; calculating a second correction factor based on ionization chamber rod scattering; creating a conversion factor from air kerma energy to 1cm water absorbed dose at the measurement point; and calculating the water absorption dose rate at the position of 1cm. The active measurement method is adopted, the ionization chamber is used for measuring the absorbed dose of the rays generated by the spherical source applicator in water, namely the measured value is the absorbed dose at the position of 1 cm in water, the advantages of being easy to operate and short in measurement time are achieved, real-time reading can be achieved, and waiting is not needed.

Description

Technical Field

[0001] This invention relates to the field of X-ray water absorbent measurement technology, and in particular to a method for measuring the water absorbed dose of Intrabeam during intraoperative radiotherapy based on air kerma. Background Technology

[0002] With the continuous development of clinical medicine and the constant updating and application of medical diagnostic and treatment technologies, intraoperative radiation therapy (IORT) has been widely used in the field of tumor treatment. The Intrabeam system consists of an X-ray source, control console, photodiode array, ionization chamber for quality control, and water tank. Different applicators are used depending on the type and shape of the tumor being treated, with a 4cm diameter spherical applicator being the most commonly used clinically. The X-ray tube is the core component; it is a small accelerator operating at 50kV and 40μA, generating X-rays through bremsstrahlung radiation using electron beams.

[0003] Before clinical treatment, it is necessary to accurately determine the absorbed water dose output by the Intrabeam system to provide the prescribed dose to the patient. Absorbed water dose is defined as the average energy imparted to water of mass dm by ionizing radiation. For the Intrabeam system, the quantity to be measured is the absorbed water dose at a depth of 1 cm.

[0004] Passive dosimeters (such as film dosimeters and thermoluminescent dosimeters) require pre-calibration of the dose-density relationship curve. The accuracy of measurement results fluctuates significantly due to factors such as calibration precision and environmental conditions. After use, the data must be allowed to stand for 24 hours before it can be read out using a dedicated device, making real-time dose values ​​impossible. The entire process is time-consuming and inefficient. Furthermore, post-measurement processing (such as reading and calculation) is required to obtain the dose value, hindering immediate feedback and impacting timeliness in clinical use. Therefore, a method for measuring the intraoperative water-absorbed dose of Intrabeam radiotherapy based on air kerma is needed. Summary of the Invention

[0005] The purpose of this invention is to provide a method for measuring the intraoperative water absorption dose of Intrabeam radiotherapy based on air kerma, which can reduce the fluctuation in the accuracy of the measurement results.

[0006] To achieve the above objectives, the present invention is implemented according to the following technical solution:

[0007] The first aspect of this invention provides a method for measuring the water absorption dose of Intrabeam during intraoperative radiotherapy based on air kerma, comprising the following steps:

[0008] Characterize the spectrum; select a radiative quality that matches or closely approximates the spectrum, and characterize the energy spectrum of the radiative quality;

[0009] Obtain the measurement parameters of air kerma rate; calculate the first correction factor using the Monte Carlo method; calculate the second correction factor based on rod scattering in the ionization chamber; and create a conversion factor from air kerma rate at the measurement point to the 1cm water absorption dose.

[0010] The formula for calculating the water absorption dose rate at a depth of 1 cm is as follows:

[0011] D W =k Q ·K air,IB ·F K,D ·k stem

[0012] Where, k stem As the second correction factor, F K,D k is the conversion factor. Q K is the first correction factor. air,IB For measuring air kerma rate.

[0013] Furthermore, the first correction factor k of the radiation quality was adjusted using the Monte Carlo method. Q The calculation is performed using the following formula:

[0014]

[0015] In the formula: D gas The absorbed dose within the sensitive volume of the ionization chamber; K a Q is the air kerma of the ionization chamber; Q0 is the reference radiation mass; Q is the radiation mass of the system at 1 cm water when equipped with a spherical emitter.

[0016] Furthermore, the feature is that the ionization chamber is calibrated based on a reference radiation quality to obtain the calibration coefficient Nk;

[0017] The ionization current I in the ionization chamber is obtained in the radiation field of the Intrabeam source, and the air levitation rate K is calculated. air,IB The formula is as follows:

[0018] K air,IB =N K I

[0019] Where I is the ionization current, N k This is the calibration coefficient.

[0020] Furthermore, the second correction factor is calculated as follows:

[0021] The ionization chamber response was measured under different radiation field conditions in a reference radiation field, and then a curve of ionization chamber response versus radiation field size was established.

[0022] The Intrabeam radiation field was measured, and the size of the radiation field was substituted into the curve of the ionization chamber response versus the size of the radiation field to obtain the response R2 of the ionization chamber.

[0023] Based on the response R1 of the ionization chamber under calibration conditions, the second correction factor k is calculated. stem =R1 / R2;

[0024] Furthermore, the radiometric material is CCRI 50b radiometric material; the spherical applicator is 4 cm.

[0025] Compared with the prior art, the embodiments of the present invention have at least the following advantages or beneficial effects:

[0026] This invention employs an active measurement method, utilizing an ionization chamber to measure the absorbed dose of radiation generated by a spherical applicator in water. The measured value is the absorbed dose at a depth of 1 cm in water. It has the advantages of simple operation, short measurement time, and real-time reading without waiting. Attached Figure Description

[0027] Figure 1 This is a flowchart illustrating the key steps of an embodiment of the present invention;

[0028] Figure 2 This is a schematic diagram of the Intrabeam fluence spectrum data of the reference radiation quality (CCRI 50b) and a 4cm spherical applicator + 1cm water in this invention; Detailed Implementation

[0029] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0030] Reference Figure 1 As shown, this invention provides a method for measuring the intraoperative water absorption dose of Intrabeam radiotherapy based on air kerma, comprising the following steps:

[0031] Characterize the spectrum; select a radiative quality that matches or closely approximates the spectrum, and characterize the energy spectrum of the radiative quality;

[0032] Obtain the measurement parameters of air kerma rate; calculate the first correction factor using the Monte Carlo method; calculate the second correction factor based on rod scattering in the ionization chamber; and create a conversion factor from air kerma rate at the measurement point to the 1cm water absorption dose.

[0033] Calculate the water absorption dose rate at 1 cm.

[0034] The specific steps in this implementation example are as follows:

[0035] Step 1: Characterize the photon energy spectrum of the INTRABEAM source equipped with a 4cm spherical donor and 1cm of water;

[0036] Step Two: Select or construct a reference radiation quality that closely approximates the energy spectrum characterized in Step One. Figure 2 As shown, CCRI 50b radiometric material is selected in this invention;

[0037] Radiative matter Tube voltage / kV Tube current / mA Half-value layer / mmAl CCRI50b 50 12 1.012

[0038] Step 3: Compare the energy spectrum obtained in Step 1 with the energy spectrum obtained in Step 2.

[0039] The correction factor k for these two radioactive materials was determined using the Monte Carlo method. Q Perform calculations;

[0040]

[0041] In the formula: D gas The absorbed dose within the sensitive volume of the ionization chamber; K a Q is the air kerma of the ionization chamber; Q0 is the reference radiation mass; Q is the radiation mass of the Intrabeam system at 1 cm water when equipped with a 4 cm spherical emitter.

[0042]

[0043]

[0044] Select an ionization chamber (PTW 23342), and perform ionization chamber calibration using the reference radiation quality from step two to obtain the calibration coefficient N. k ;

[0045] I ionization current was measured using an ionization chamber in the Intrabeam source radiation field, and the air kerma rate was calculated using the ionization chamber. air,IB The formula is

[0046] K air,IB =N K I (1)

[0047] Step Six: Use the Monte Carlo program to create the conversion factor F from the air kerma at the measurement point to the water absorbance at 1 cm.K,D ;

[0048]

[0049] Step 7: Calculate k stem This correction factor is primarily due to the difference in radiation field size between the reference radiation field and the Intrabeam radiation field, resulting in different scattering patterns in the ionization chamber rod. The specific method involves first measuring the ionization chamber response of the PTW 23342 ionization chamber under different radiation field conditions in the reference radiation field, and then establishing a curve comparing the ionization chamber response with the radiation field size. Next, the Intrabeam radiation field is measured, and the radiation field size is substituted into the curve comparing the ionization chamber response with the radiation field size to obtain the ionization chamber response R2. Then, based on the ionization chamber response R1 under the calibration conditions in step three, k is obtained. stem =R1 / R2;

[0050] Step 8 calculates the water absorbed dose rate at 1 cm based on air kerma and radiation quality correction factor. The core idea is to use the existing air kerma rate under radiation quality, radiation quality conversion factor, and air kerma to water absorbed dose conversion factor to measure the water absorbed dose.

[0051] D W =k Q ·K air,IB ·F K,D ·k stem (2)

[0052] In the formula: D W k is the water absorption dose rate. stem The second correction factor (ionization chamber rod correction factor) is used to take into account the difference between the radiation field size under the reference radiation quality and the actual measured radiation field size. This difference will cause the scattering contributions of the ionization chamber rod and the main body to differ. K,D k is the air kerma conversion factor to water absorbed dose calculated by MC simulation. Q K is the first correction factor (radiation quality correction factor). air,IB For measuring air kerma rate.

[0053] The above description is merely an example and illustration of the structure of the present invention. Those skilled in the art can make various modifications or additions to the specific embodiments described, or use similar methods to replace them, as long as they do not deviate from the structure of the invention or exceed the scope defined in the claims, all of which should fall within the protection scope of the present invention.

Claims

1. A method for measuring the water absorption dose of Intrabeam during intraoperative radiotherapy based on air kerma, characterized in that, Includes the following steps: Characterize the spectrum; select a radiative quality that matches or closely approximates the spectrum, and characterize the energy spectrum of the radiative quality; Obtain the measurement parameters of air kerma rate; The first correction factor was calculated using the Monte Carlo method; The second correction factor is calculated based on rod scattering in the ionization chamber; a conversion factor is created from the air kerma at the measurement point to the water absorbed dose at 1 cm. The formula for calculating the water absorption dose rate at a depth of 1 cm is as follows: D W =k Q ·K air,IB ·F K,D ·k stem Where, k stem As the second correction factor, F K,D k is the conversion factor. Q K is the first correction factor. air,IB For measuring air kerma rate.

2. The method for measuring the intraoperative water absorption dose of Intrabeam radiotherapy based on air kerma as described in claim 1, characterized in that, The first correction factor k of the radiometric quality using the Monte Carlo method Q The calculation is performed using the following formula: In the formula: D gas The absorbed dose within the sensitive volume of the ionization chamber; K a Q is the air kerma of the ionization chamber; Q0 is the reference radiation mass; Q is the radiation mass of the system at 1 cm water when equipped with a spherical emitter.

3. The method for measuring the intraoperative water absorption dose of Intrabeam radiotherapy based on air kerma as described in claim 1, characterized in that, Ionization chamber calibration was performed based on reference radiation quality to obtain calibration coefficient N. k ; The ionization current I in the ionization chamber is obtained in the radiation field of the Intrabeam source, and the air kerma rate measurement K is calculated. air,IB The formula is as follows: K air,IB =N K I Where I is the ionization current, N k This is the calibration coefficient.

4. The method for measuring the intraoperative water absorption dose of Intrabeam radiotherapy based on air kerma as described in claim 1, characterized in that, The second correction factor is calculated as follows: The ionization chamber response was measured under different radiation field conditions in the reference radiation field, and then a curve of ionization chamber response versus radiation field size was established. The Intrabeam radiation field was measured, and the size of the radiation field was substituted into the curve of the ionization chamber response versus the size of the radiation field to obtain the response R2 of the ionization chamber. Based on the response R1 of the ionization chamber under calibration conditions, the second correction factor k is calculated. stem =R1 / R2.

5. The method for measuring the intraoperative water absorption dose of Intrabeam radiotherapy based on air kerma as described in claim 1, characterized in that, The radiometric material is CCRI50b radiometric material; the diameter of the spherical applicator is 4 cm.

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