CN111474572A

CN111474572A - Finger-shaped ionization chamber for measuring high-energy photon water dosage distribution

Info

Publication number: CN111474572A
Application number: CN202010444675.0A
Authority: CN
Inventors: 龚岚; 张从华; 刘操; 黄秋; 杨勇
Original assignee: Institute Of Radiation Research China Academy Of Testing Technology
Current assignee: Institute Of Radiation Research China Academy Of Testing Technology
Priority date: 2020-05-23
Filing date: 2020-05-23
Publication date: 2020-07-31

Abstract

A finger-shaped ionization chamber for high-energy photon water dosage distribution measurement, an outer electrode is connected to an outer electrode support rod; one end of the collector extends into the ionization cavity volume, and the other end of the collector is connected to the collector plug; one end of the collector plug tightly clamps the collector, and the other end of the collector plug is welded on the inner core of the cable; one end of the protective electrode is tightly pressed and connected to the protective ground of the cable through the brim, and the other end of the protective electrode extends to the edge of the sensitive volume to be flush; the cable penetrates through the first insulator and then is connected to the collector and the protective electrode; one end of the outer electrode supporting rod is an internal thread connected with the locking stud, and the other end of the outer electrode supporting rod is an external thread connected to the outer electrode. The invention has the advantages of small inter-polar distance, stability, easy determination of effective measuring points and the like, and has obvious advantages and higher measuring precision on the calibration of photon absorption dose and the measurement of a region with larger dose gradient change along the incident direction of the beam.

Description

Finger-shaped ionization chamber for measuring high-energy photon water dosage distribution

Technical Field

The invention relates to the field of detection of dose distribution of high-energy photon rays in water, in particular to a finger-shaped ionization chamber for measuring the dose distribution of high-energy photon rays in water.

Background

The medical linear accelerator is an accelerating device which accelerates electrons by using a microwave electromagnetic field and has a linear motion track, is mainly used for radiotherapy of tumor patients, and is widely used at present. However, for the detection of the dose distribution of high-energy photon rays in water, the ionization chamber is required to have small measuring points, the peak value of point dose can be accurately reflected, and particularly, the conventional famer graphite type finger-shaped ionization chamber cannot meet the measuring requirement in places with large dose gradient change in water.

In 1958, article of conductive plastic equivalent tissue, air and polystyrene was published by Shonka, F.R, Rose, j.e, Failla, G and the like, research on air equivalent plastic was developed, and air equivalent material was applied to the manufacturing of ionization chambers. The wall of the ionization chamber is made of air equivalent material, has approximately the same absorption coefficient to primary radiation and air and approximately the same atomic stopping power to secondary electrons, has firm, durable and stable physical characteristics, and is an excellent material for manufacturing the ionization chamber.

The development of air equivalent materials in foreign countries starts very early, and existing products are available, such as: c-552 air equivalent material. Air equivalent materials have been used abroad for the production of standard ionization chambers, such as FC23-C Farmer, PR-06CFarmer, PR-06G Farmer, and the like. The radiation technology limited company for measuring in Sichuan is engaged in the research and development of the material, and the produced CT long-rod ionization chamber is already used for CT dose measurement, and the energy response is less than 3 percent.

At present, the finger-shaped ionization chamber is generally adopted in China to measure the radiation dose of high-energy photons, but the finger-shaped ionization chamber has large sensitive volume and cannot truly reflect the characteristic of steep change of dose distribution in water. The finger-shaped ionization chamber for measuring the dose distribution in water is specially used abroad, but the outer electrode of the finger-shaped ionization chamber adopts an organic glass coated graphite conductive layer, the effective atomic number of the conductive layer is slightly smaller than that of air, and therefore, the ionization charge generated in the cavity is slightly less than that of a free air ionization chamber. Overall, the disadvantages of the prior art are mainly two: 1. the measurement is usually carried out by using a finger-type ionization chamber with a large cavity volume. At present, a finger-shaped ionization chamber is generally adopted for measuring water absorbed dose in China, but under the condition of steep radiation dose change, the finger-shaped ionization chamber with a large cavity volume needs to smooth a dose curve, and the characteristic of radiation beam gradient change cannot be truly reflected. 2. Organic glass coated graphite is used as a chamber wall material. There is a special ionization chamber with small cavity volume abroad, but the wall of the ionization chamber is made of organic glass coated graphite conductive layer, the effective atomic number of the ionization chamber is slightly less than that of air, so the ionization charge generated in the cavity is slightly less than that of the free air ionization chamber.

Related terms

An ionization chamber: an ionization detector for an appropriate gas contained within a sensitive volume, an electric field applied between the detector electrodes and of insufficient strength to cause amplification of the gas, but capable of collecting on the electrodes electrons, ion-related charges generated within the sensitive volume by ionizing radiation.

Disclosure of Invention

The invention aims to solve the technical problem of providing a finger-shaped ionization chamber for measuring the dose distribution in high-energy photon water, which adopts air equivalent plastic as a chamber wall material and epoxy resin as an adhesive, has the advantages of small inter-polar distance, stability, easy determination of effective measuring points and the like, and has obvious advantages and higher measuring precision on the calibration of photon absorption dose and the measurement of a region with larger dose gradient change along the incident direction of a beam.

In order to solve the technical problems, the invention adopts the technical scheme that:

a finger-shaped ionization chamber for measuring the dose distribution in high-energy photon water comprises an outer electrode, an outer electrode supporting rod, a collector and a protective electrode, wherein the outer electrode is connected to the outer electrode supporting rod to form an independent ionization cavity; one end of the collector extends into the ionization cavity volume, and the other end of the collector is connected to the collector plug; one end of the collector plug tightly clamps the collector, and the other end of the collector plug is welded on the inner core of the cable; one end of the protective electrode is tightly pressed and connected to the protective ground of the cable through the brim, and the other end of the protective electrode extends to the edge of the sensitive volume to be flush; the insulator is provided with a first insulator, a second insulator, a third insulator and a fourth insulator; the third insulator is plugged into the fourth insulator, the second insulator isolates the protective electrode from the outer electrode, and the cable passes through the first insulator and then is connected to the collector and the protective electrode; one end of the outer electrode supporting rod is an internal thread connected with the locking stud, and the other end of the outer electrode supporting rod is an external thread connected to the outer electrode.

Further, the outer electrode is made of an air equivalent material.

Furthermore, the top end of the outer electrode is a hemisphere, and the diameter of the hemisphere is the same as that of the cylinder.

Furthermore, the collector is made of pure aluminum with the diameter of 1 mm.

Further, the collector plug is plated with gold by pure copper, and the surface of the collector plug is provided with a welding hole.

Further, the first insulator, the second insulator, the third insulator and the fourth insulator are all processed by polychlorotrifluoroethylene.

Furthermore, the locking stud is machined from copper.

Further, the external seams of the whole finger ionization chamber are bonded by epoxy resin.

Compared with the prior art, the invention has the beneficial effects that: 1. the device has the characteristic of small sensitive volume and can truly reflect the gradient change of the radiation beam. 2. The air equivalent material is used as an outer electrode, so that the measurement is more accurate. 3. The structure has the advantages of simple assembly, good contact and less air gap, improves the consistency of the cavity ionization chamber, improves the qualification rate of products, and simultaneously realizes the firmness and the durability of the products.

Drawings

FIG. 1 is a cross-sectional view of a finger ionization chamber structure for high energy photon in-water dose distribution measurement according to the present invention.

Fig. 2 is a perspective view of a finger ionization chamber structure for high-energy photon water dose distribution measurement according to the present invention.

In the figure: 1-locking stud, 2-outer electrode support rod, 3-first insulator, 4-second insulator, 5-third insulator, 6-fourth insulator, 7-protective electrode, 8-collector plug, 9-collector and 10-outer electrode.

Detailed Description

The present invention will be described in further detail with reference to the accompanying drawings and specific embodiments. The invention designs a finger-shaped ionization chamber, which adopts air equivalent materials as an ionization chamber outer electrode to keep the firmness and durability of the ionization chamber; the collector 9 is made of pure aluminum material with the diameter of 1mm, and the outer electrode 10 is made of air equivalent material to form an ionization air cavity. The volume of the air cavity is composed of a cylinder with the diameter of 5mm and a hemisphere, the length of the cylinder is 5mm, the diameter of the hemisphere is 5mm, and the protective electrode 7 extends to the edge of the sensitive volume to be flushed, so that the stability of collecting charges by the collector is ensured, and leakage current is reduced.

Specifically, the structure of the invention is as follows:

the outer electrode 10 is made of an air equivalent material, has a smooth surface, is connected to the outer electrode support rod 2 to form an independent electric field space, reduces the interference of an outer electric field, and has a hemispherical top end with the same diameter as a cylinder, thereby ensuring good directivity and angular response; the collector 9 is made of pure aluminum (with the purity of 99.99%) with the diameter of 1mm, is easy to process and small in deformation, one end of the collector extends into the volume of the ionization cavity to collect charges, and the other end of the collector is connected to the collector plug 8; the collector plug 8 is fastened to the collector 9 at one end and transfers the collected charge to the host by welding the other end to the inner core of the cable. The collector 9 plug is plated with gold by pure copper, and the surface of the collector is provided with a welding hole, so that the welding is convenient; one end of the protective electrode 7 is tightly pressed and connected to a protective ground of the cable through a cap brim, and the other end of the protective electrode extends to the edge of the sensitive volume to be flush, so that the distortion of an electric field is reduced, the stability of collecting electric charges by the collector 9 is ensured, and the leakage current is reduced; the fourth insulator 6 isolates the protective electrode 7 and the collector 9, is processed by polychlorotrifluoroethylene, and has smooth appearance, strong insulation and high hardness; the third insulator 5 is a small plug and is plugged into the fourth insulator 6 to prevent the collector 9 and the guard electrode 7 from short circuit, and is processed by adopting polychlorotrifluoroethylene, so that the appearance is bright and clean, the insulativity is strong, and the hardness is high; the second insulator 4 isolates the protective electrode 7 and the outer electrode 10, is processed by polychlorotrifluoroethylene, and has smooth appearance, strong insulation and high hardness; the cable passes through the first insulator 3 and then connects to the collector 8 and the guard 7; the first insulator 3 is processed by polychlorotrifluoroethylene, and has smooth appearance, strong insulation and high hardness; the outer electrode support rod 2 is processed by aluminum alloy, one end of the outer electrode support rod is provided with an internal thread which is convenient for connecting the locking stud 1, and the other end of the outer electrode support rod is provided with an external thread which is connected to the outer electrode 10, so that the outer electrode support rod is convenient for fixing a clamp for connecting high voltage to the outer electrode 10; the locking stud 1 is formed by processing copper, one end of the locking stud is provided with a knurled thread to facilitate screwing, the other end of the locking stud is provided with an external thread, a high-voltage pole wire of a compression cable is connected to the external electrode support rod 2 to transmit voltage to an external electrode, and the locking stud 1 is used for compressing the high-voltage wire and locking an internal structure to prevent the structure from loosening; seams outside the ionization chamber are bonded by epoxy resin to ensure good waterproof performance.

Although the present invention has been described in detail with reference to the preferred embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the spirit and scope of the invention as defined in the appended claims.

Claims

1. A finger-shaped ionization chamber for measuring the dose distribution in high-energy photon water is characterized by comprising an outer electrode (10), an outer electrode support rod (2), a collector (9) and a protective electrode (7), wherein the outer electrode (10) is connected to the outer electrode support rod (2) to form an independent ionization cavity;

one end of the collector (9) extends into the ionization cavity volume, and the other end is connected to a collector plug (8); one end of the collector plug (8) is tightly clamped with the collector (9), and the other end is welded on the cable inner core; one end of the protective electrode (7) is tightly pressed and connected to the protective ground of the cable through the brim, and the other end of the protective electrode extends to the edge of the sensitive volume to be flush;

the insulator is provided with a first insulator (3), a second insulator (4), a third insulator (5) and a fourth insulator (6); the fourth insulator (6) isolates a protective electrode (7) and a collector (9), the third insulator (5) is plugged into the fourth insulator (6), the second insulator (4) isolates the protective electrode (7) and an outer electrode (10), and a cable passes through the first insulator (3) and is connected to the collector (8) and the protective electrode (7);

one end of the outer electrode supporting rod (2) is an internal thread connected with the locking stud (1), and the other end of the outer electrode supporting rod is an external thread connected to the outer electrode (10).

2. A fingered ionization chamber for high energy photon in water dose distribution measurement according to claim 1, characterized by the fact that the outer electrode (10) is made of air equivalent material.

3. A fingered ionization chamber for high energy photon in water dose distribution measurement according to claim 1, characterized by that, the top of the outer electrode (10) is a hemisphere with the same diameter as a cylinder.

4. A fingered ionization chamber for high-energy photon in-water dose distribution measurement according to claim 1, characterized by the fact that the collector (9) is made of pure aluminum with a diameter of 1 mm.

5. A fingered ionization chamber for high energy photon in water dose distribution measurement as per claim 1, characterized by the collector plug (8) gold plated with pure copper and with solder holes on the surface.

6. A fingered ionization chamber for high-energy photon in-water dose distribution measurement according to claim 1, characterized in that the first insulator (3), the second insulator (4), the third insulator (5) and the fourth insulator (6) are all processed with polychlorotrifluoroethylene.

7. The fingered ionization chamber for high-energy photon in-water dose distribution measurement according to claim 1, characterized in that the locking stud (1) is machined from copper.

8. The fingered ionization chamber for high energy photon in-water dose distribution measurement according to claim 1, wherein the entire fingered ionization chamber is bonded at its external seams with epoxy.