RU2786345C1 - Method for controlling beam parameters during proton therapy and device for its implementation - Google Patents

Abstract

FIELD: radiation therapy.

SUBSTANCE: inventions group relates to the field of radiation therapy using protons. The method for controlling the beam parameters in the process of proton therapy additionally comprises the steps at which the measurement of the beam parameters is carried out by irradiating each area of the surface of the coordinate-sensitive plane of the multichannel pad ionization chamber and the plane of the phosphor screen located in front of it, divided into cells that coincide in geometric dimensions with the surface area a multichannel pad ionization chamber, while additionally identifying and reading the beam parameters by means of a digital video camera, a cell number analyzer and an analog multiplexer.

EFFECT: increasing the accuracy of determining the dose released in the target for each pulse of the accelerator, increasing reliability, simplifying the design.

4 cl, 2 dwg

Description

Technical field

The present invention relates to the field of radiation therapy using protons, and can be used for practical dosimetry in determining the absorbed dose from a proton beam for medical purposes, in particular, for proton therapy when irradiating large pathological foci with a low-intensity "pencil beam" with high dose adjustment accuracy to the source area along the coordinate.

Prior Art

From the dissertation “Development of optical diagnostic methods in cyclic particle accelerators”, Dorokhov V.L., publ. 2021, a method for measuring the beam profile is known, which is carried out using a phosphor screen placed in the vacuum chamber of the accelerator in front of a fast video camera recording the luminous beam profile. The visible light emitted by the phosphor screen as the beam passes through it is recorded and measured by a digital video camera, and the resulting image is displayed on a computer.

From patent RU2654838, publ. 22.05.2018, and patent RU179244, publ. 05/07/2018, a device is known for controlling the proton and ion beam before a proton therapy session and a method for measuring the energy release from ionizing radiation. The device for measuring the energy release from ionizing radiation, disclosed in the above patents, namely the digital imaging detector (CDPI), after monitoring the beam of the proton accelerator, is moved out of the beam and a patient is placed in its place for a proton therapy session. The CDPI device allows, in the range of all therapeutic energies of a scanning low-intensity proton beam with an accuracy regulated by the IAEA, to restore the depth of the Bragg peak for the upcoming control of the dose field in depth and width before irradiating the patient for an accelerator pulse [Series of technical reports No. 398. Absorbed Dose Determination in External Beam Therapy: International Practice Guidelines for Dosimetry Based on Absorbed Dose Unit Standards in Water, IAEA, Vienna, 2004].

A known method for controlling beam parameters in the process of proton therapy, known from patent SU1338154, publ. One camera is installed after the last quadrupole lens, and the second in front of the patient. The disadvantages of this method include low accuracy in determining the flow of protons passing through them, and the inability to determine the total dose of proton particles that have passed through them per full pulse of the accelerator.

The closest analogue is the method and device for controlling beam parameters in the process of proton therapy known from patent RU2747365, publ. which turns off the accelerator beam when the profile deviates from the profiles specified in the system. The disadvantage of the prototype is the complexity of the device itself and the readout electronics and the SCOO system.

Disclosure of the essence of the invention

The objective of the invention is to increase the conformity of the control of the process of irradiation of the patient during a proton therapy session, namely, the accuracy of monitoring the correspondence of the radiation beam to the pathological focus, when determining the profile of the absorbed dose along the x- and y-coordinates.

The technical result of the invention is to increase the accuracy in determining the dose released in the target for each pulse of the accelerator. In addition, increasing the reliability, reducing the cost of the device, simplifying the design by simplifying the design of the readout electronics while maintaining a large number of camera channels.

The claimed technical result is achieved in a method for controlling beam parameters in the process of proton therapy, including measuring the allowable values of dose profiles and beam intensity density before irradiating the patient using a pad chamber installed between the last scanning magnet and the patient, quantitative comparison of the measured dose profiles and beam intensity density with allowable values, and turning off the beam when the parameters deviate from the allowable values, while the measurement of the beam parameters is carried out by irradiating each area of the surface of the coordinate-sensitive plane of the multichannel pad ionization chamber and the plane of the phosphor screen located in front of it, divided into cells that coincide in geometric dimensions with the area surfaces of the multichannel pad ionization chamber, while additionally identifying and reading the beam parameters and processing the beam parameters by means of a digital video camera, cell number analyzer and analog multiplexer.

The claimed technical result is achieved by using a beam parameters control device in the process of proton therapy, including an accelerator with a proton beam focused by quadrupole lenses, a pad camera installed between the last scanning magnet and the patient, reading electronics for signal processing from the camera, and an electronic circuit for comparison and detection control deviations, while a multichannel pad ionization chamber is used as a camera, the coordinate-sensitive plane of which is divided into sections, and a phosphor screen installed in front of it, the plane of which is divided into cells that match in size with the sensitive areas of the camera, while additionally includes a digital video camera , cell number analyzer and analog multiplexer.

A digital video camera, together with a cell number analyzer, identifies the cell number on the phosphor screen through which the beam spot has passed, the cell number analyzer generates a code for the number of the surface area of the coordinate-sensitive plane of the multichannel pad ionization chamber and transmits it to an analog multiplexer connected via current outputs to each surface area camera, and the analog multiplexer transmits the beam parameters to the readout electronics for processing and comparing the parameters with acceptable values.

The claimed invention uses one large multi-channel ionization pad chamber, and a control and deviation detection circuit (OCDS). The COMS has a smaller number of controllable parameters during a proton therapy session than in analogs, which simplifies the process of conducting a therapy session and processing the results. The main essential distinguishing feature of the proposed invention is a fundamentally different electronic reading of beam profiles during target irradiation.

A distinctive feature of the proposed device is the use of a large multichannel ionization pad chamber (MIC) with a coordinate-sensitive plane divided into sections, which is installed between the last scanning magnet and the patient, and an electronic cell number analyzer that determines the number of the "triggered" section of the chamber surface, which is transmitted to the reading electronics (SE).

The entire sensitive surface of the multichannel pad ionization chamber is divided into N-sections, with each surface section containing only a part of the sensitive pads (for example, in Fig.2, 5x5, i.e. 25 pads). The scanning beam sequentially passes through all sensitive areas, each of which has its own number from 1 to N. When the beam passes through each area, the reading electronics collects information only from a small part of the channels of the pad chamber, namely from n-pads included in the area of the chamber surface , which significantly reduces the number of channels for processing by the readout electronics. Therefore, a multi-channel pad chamber can also be called "phased", i.e. divided into separate independent sensitive areas.

The main feature is the ability to determine the coordinates of the area where the scanning beam passes for a given spot of the beam. Inside the camera device (MIC), in front of each area with n-pads, a phosphor screen is installed, which, using a grid applied to the screen, is divided into cells that match in size with the sensitive areas of the MIC camera plane and determine which area of the camera surface the spot passed through. The read-out electronics (SE) of the MIC camera reads the profile from one of the sensitive sections of the MIC camera plane, and after checking it on the control and deviation detection circuit (SCDS), transfers the profile to the computer. The OCCS system is made in a simplified form with a smaller number of controlled parameters, which makes it possible to simplify the training of maintenance personnel, which also significantly reduces the cost of the device.

Description of the invention

The general scheme of the proposed device is shown in Fig.1. The device includes a synchrotron-type accelerator (1) with a proton beam (2) for irradiating a target (3), for example, a tumor. To bind the position of the target (3) to the beam axis, the coordinate system xyz (4) was introduced. The proton beam extracted from the accelerator (1), focused by two quadrupole lenses (5), passes through the scanning magnets (6). The coordinate-sensitive MIC camera (7) (the area is indicated by a dotted line) is located between the second scanning magnet and the irradiated target (3) (7), consists of a coordinate-sensitive plane (9) divided into sensitive areas (19) and a phosphor screen ( 8) located in front of the plane (9). Each section (19) contains n-pads (10). The planes of the phosphor screen (8) and the coordinate-sensitive plane of the camera (9) divided into sections are perpendicular to the z-axis (11). The proton scanning beam (2) from the accelerator, divided into spots, sequentially irradiates the section (19) of the MIC ionization chamber (7). The z(11) axis, which determines the depth, strictly passes through the center of the axial cell of the phosphor screen (8) and through the center of the axial section of the sensitive surface of the MIC chamber (9).

The x-axis (12) determines the width, and the y-axis (13) determines the height. The phosphor screen (8) is divided into cells (14) in the form of a grid deposited on the screen (8). Each of the cells (14) of the phosphor screen (8) is displayed on the frame of a fast digital video camera (15), for example, GigaVision. The cell numbers of the phosphor screen (8) through which the beam spot passed are identified by a fast digital video camera (15) and a cell number analyzer (16). The cell number analyzer (16) outputs a code to an analog multiplexer (17), which is connected via current leads (18) to each of the sensitive areas (19) of the sensitive area of the MIC chamber (9). The cell number analyzer (16) generates the code for the number of the section through which the beam passed during the current spot. The maximum value of the cell number of the phosphor screen (8) is N, and inside each of the sensitive sections of the camera plane there are n-coordinate-sensitive pads (10).

Figure 1 shows two spot beams of the beam (2), one of the beams passes through the number N(i) (20) cells (14) of the phosphor screen (8) and the sensitive surface of the camera (9). The second spot beam, for example, passes through the number N(i+4) (21) cells (14) and "phases" (19). Moreover, for any spot beam, the number of the cell of the phosphor screen (8) and the number of the section of the sensitive area of the MIC camera (9) always coincide. Geometrically, the dimensions and position of the sensitive areas of the MIC coincide with the boundaries of each corresponding cell of the phosphor screen (8). Therefore, if the spot of the beam has passed through some section number with N(i) (20), then the luminous spot will be detected by the camera (15) on the phosphor screen (8) in the cell with the same number N(i) (20). After determining the number of the cell with a luminous spot using the analyzer (16), the number N(i) is determined, which is transmitted in the form of a code to the analog multiplexer (17), the number of inputs (18), which is equal to N and coincides with the number of sensitive areas on the surface in the MIC chamber (9). Signals (18) from each sensitive section of the MIC chamber, where the beam profile is recorded on the n-pads of each “triggered” section of the MIC surface, are fed to the input of the analog multiplexer (17) and, according to the code of the received number, are sent to the reading electronics (22). Starting the reading electronics initiates the accelerator (1). For each release of the accelerator for scanning magnets, the scanning "pencil beam" irradiates the target (3) according to a given program. The integrated signals for each spot from the sensitive area of the MIC chamber surface (9) are read through the analog multiplexer (17) into the memory buffer of the reading electronics (22). Control each spot passing through each sensitive area of the chamber in one release. For one spot passing through the sensitive area of the MIC chamber (7), two-dimensional profiles (x, y) and densities (dose profiles) are measured. The readout electronics memory buffer stores profile and density information for each sensitive area. Further, the data for all sections for one complete release of the accelerator is transmitted to the deviation control and detection circuit (OCDS) (23). During the calibration of the MIC chamber (7), admissible values of beam profiles and densities are recorded in advance on the RMSD scheme (23). The RMSD circuit (23) is connected to a programmable matrix (24), in which the applied algorithms are programmed, which determine the state of the passing beam per pulse. If the RMSD circuit (23) and the programmable FPGA matrix (24) detect during control a deviation of the allowable and measured parameters, then the matrix (24) turns off the beam. If no deviations are detected during the release of the accelerator, then the beam profiles for one release of the accelerator are transmitted via the communication line (25) to the computer (26) for recording and visualization. The main control signals from the accelerator are transmitted via line (27). The scheme of the "phase" device and control of the beam stability during the irradiation of the patient (target) is illustrated in Fig.2.

Example 1 Implementation of a method for monitoring the detection of deviations.

The operator sets the controlled parameters in the program of the programmable matrix (24). As a coordinate and dose meter, a pad chamber MIC (7) is used with an N-number of sensitive areas, each of which has n-pads. The control of dose parameters of the beam is explained in Fig.2. The boundary of the "triggered" sensitive area (19) of the MIC surface, through which the beam spot passed, is marked (28).

The beam spot that passed through the sensitive area is designated as (29). One pad inside the site is indicated as (30). The MIC pad chamber determines not only the x and y coordinates, but also the dose of each spot. Therefore, figure 2 on the right shows the dose profile, which measured the sensitive area, for the spot along the x and y coordinates. The spot of the beam passed through pad number 4 along the x coordinate and number 3 along the y coordinate. On FIG. 2 d20, d50, d80 and d90 (33) are dose parameters used in clinical proton therapy. For control, we select the parameter d50 - the dose at the level of 50% of the measured profile along the x and y coordinates (34). Figure 2 shows 5x5 pads in one sensitive area. The profiles are given along the x(31) and y(32) coordinates, measured by the site, and transmitted over the spot through the reading electronics to the computer.

From the dose profiles measured by the MIC camera for each spot for the full release of the accelerator, doses are calculated at the level of 50% of the distribution maximum, the so-called medical parameter d50.

d (x,y)50L= f(x,y) - dose on the left wing of the dose profile at the level of 50% of the maximum, measured by the camera for coordinates x and y;

d (x,y)50R= f(x,y) - dose on the right wing of the dose profile at the level of 50% of the maximum, measured by the camera for x and y coordinates;

We calculate the controlled parameter (1) according to the following relations:

Кx,y= d(x,y)50L/ d(x,y)50R (1)

The parameter Kx,y is controlled by the RMSD scheme and recorded in the computer for each release of the accelerator. The ratio of this parameter is most sensitive for any beam deflection during target irradiation according to a given program. If parameter (1) deviates from the specified one, the accelerator will be switched off. If this parameter goes beyond the limits set by the operator in the programmable FPGA matrix, the COMS circuit gives a signal to turn off the accelerator. The method makes it possible to achieve full compliance between the planned parameters of the medical proton beam and those actually used in the patient's irradiation session.

Claims (4)

1. A method for controlling beam parameters in the process of proton therapy, including measuring the allowable values of dose profiles and beam intensity density before irradiating a patient using a pad chamber installed between the last scanning magnet and the patient, quantitative comparison of the measured dose profiles and beam intensity density with allowable values, and turning off the beam when the parameters deviate from the permissible values, characterized in that the measurement of the beam parameters is carried out by irradiating each area of the surface of the coordinate-sensitive plane of the multichannel pad ionization chamber and the plane of the phosphor screen located in front of it, divided into cells that coincide in geometric dimensions with the surface area a multichannel pad ionization chamber, while additionally identifying and reading the beam parameters by means of a digital video camera, a cell number analyzer and an analog multiplexer. 2. The method according to claim 1, characterized in that the digital video camera, together with the cell number analyzer, identifies the cell number on the phosphor screen through which the beam spot has passed, the cell number analyzer generates a code for the number of the surface area of the coordinate-sensitive camera plane and transmits it to the analog multiplexer connected via current leads to each section of the chamber plane, and the analog multiplexer transmits the beam parameters to the readout electronics for processing and comparing the parameters with acceptable values. 3. A device for controlling beam parameters in the process of proton therapy, including an accelerator with a proton beam focused by quadrupole lenses, a pad camera installed between the last scanning magnet and the patient, reading electronics for processing the signal from the camera, and an electronic circuit for comparing and controlling deviation detection, characterized in that that a multichannel pad ionization chamber is used as a camera, the plane of which is divided into sensitive areas, and a phosphor screen installed in front of it, the plane of which is divided into cells that match in size with the sensitive areas of the camera, while additionally includes a digital video camera, a cell number analyzer and analog multiplexer. 4. The device according to claim 3, characterized in that the digital video camera, together with the cell number analyzer, identifies the cell number on the phosphor screen through which the beam spot has passed, the cell number analyzer generates a code for the number of the sensitive area of the camera and transmits it to an analog multiplexer connected via current leads to each section of the sensitive plane of the camera, the analog multiplexer transmits the beam parameters to the readout electronics.

Images