Water phantom for water uptake dosimetry

Abstract

This invention discloses a water phantom for measuring water absorbed dose, comprising several stacked water phantom units, one of which is equipped with an ionization chamber. Each water phantom unit includes a phantom body, a first stacking positioning structure at the top, a second stacking positioning structure at the bottom, and a water storage cavity inside the phantom body. The water phantom units are stacked together through the cooperation of the first and second stacking positioning structures, and the cross-sectional size of the water storage cavity in each water phantom unit is the same. This water phantom can be used to calibrate the water absorbed dose of medical accelerators, ensuring the accuracy and reliability of radiotherapy doses and improving the radiotherapy effect for cancer patients. Compared to a water tank, this water phantom is smaller, easier to fill and position, and facilitates measurement and calibration. Compared to foreign solid water, this water phantom has lower manufacturing costs, reduced charge accumulation effects, shorter temperature equilibrium time, less impact on the ionization chamber, and more accurate measurement results.

Description

Technical Field

[0001] This invention belongs to the field of medical device technology, specifically relating to a water phantom for measuring water absorption dose. Background Technology

[0002] Cancer (i.e., malignant tumor) is a common and prevalent major disease that seriously threatens human health. Since the 1970s, the incidence of cancer has been increasing at an average annual rate of 3% to 5%, making it the second leading cause of death worldwide. The goal of cancer treatment is to cure cancer patients, prolong life, and improve quality of life. Radiotherapy, as one of the three major methods of cancer treatment, uses high-energy photon beams, electron beams, proton beams, and heavy ion beams to irradiate the tumor area. It utilizes radiobiological effects to kill cancer cells and destroy cancerous tissue to the greatest extent possible, while minimizing damage to the normal tissues surrounding the tumor. This approach aims to treat the tumor while achieving a long-term high quality of life for the patient with minimal cost.

[0003] Currently, approximately 70% of cancer patients require radiation therapy at different stages of their disease. Of these, 90% utilize medical linear accelerators. Since the human body is 70% water, the prescribed dose for radiation therapy is the water-absorbed dose, which is the energy absorbed per unit mass of water. In simpler terms, we are measuring the energy transferred to water after it has been irradiated by radiation; this is equivalent to the energy transferred to human tissues during radiation therapy.

[0004] Since water absorbed dose is the traceable physical quantity for medical linear accelerator calibration, water absorbed dose measurement has become a crucial step in the routine calibration of external irradiation equipment such as accelerators. National-level water absorbed dose benchmarks primarily use hydrocalorimetry to directly measure water absorbed dose; however, this method is costly, technically complex, time-consuming, and lacks on-site measurement capabilities. Therefore, only indirect measurement methods using an ionization chamber can be used to calibrate the water absorbed dose of clinical radiotherapy equipment. When measuring water absorbed dose using a water tank, the placement of the tank, positioning of the ionization chamber, water injection and pumping, waiting for water temperature equilibration, and post-irradiation wastewater storage are often very time-consuming and space-consuming, making it uneconomical for hospitals. For accelerator output dose calibration, existing medical water absorbed dose measurement equipment includes standard water tanks and water equivalent materials (often referred to as solid water or solid phantoms). Standard water tanks are divided into two types: open and sealed. Open water tanks are difficult to control parameters during measurement, and filling, positioning, and moving them are all very inconvenient. Sealed water tanks are an improvement over open water tanks, but the expansion of water inside the chamber and the elimination of air bubbles need to be considered. Due to their large size and weight, they are very difficult to operate and move, making them inconvenient for measurement. The strength of the water tank also needs to be considered, as long-term use may cause deformation of the water tank, resulting in inaccurate measurement results. Moreover, the large size of the water tank makes customization and transportation very inconvenient.

[0005] Solid water, a water phantom made from materials with parameters similar to water, offers greater convenience compared to direct measurement using water tanks. Its small size facilitates transportation, and the measurement only requires multiplying the final result by a correction factor, making it more suitable for measuring water absorbed dose in hospitals. However, due to the late start of domestic research on electron beam radiation water absorbed dose, currently available solid water is entirely imported, with foreign technology monopolizing the market, resulting in high prices and prohibitively high costs for calibration in medical water absorbed dose measurement. Furthermore, due to material density and properties, solid water still presents certain problems in practical applications, such as severe charge accumulation over long periods and prolonged temperature equilibrium time, significantly impacting measurement results. Therefore, solid water cannot completely replace water phantoms in routine accelerator calibration. Thus, this paper addresses the aforementioned problems with existing medical water absorbed dose measurement equipment by providing a water phantom for water absorbed dose measurement, aiming to achieve greater practical value. Summary of the Invention

[0006] The purpose of this invention is to provide a water phantom for measuring water absorption dose, in order to solve the above-mentioned problems existing in the prior art.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: a water phantom for measuring water absorption dose, comprising a plurality of stacked water phantom units, wherein one of the water phantom units is equipped with an ionization chamber, the water phantom unit comprising a phantom body, the top of the phantom body being provided with a first stacking positioning structure, the bottom of the phantom body being provided with a second stacking positioning structure, and the interior of the phantom body being provided with a water storage cavity; the various water phantom units are stacked together through the cooperation of the first stacking positioning structure and the second stacking positioning structure, and the cross-sectional size of the water storage cavity in each water phantom unit is the same.

[0008] As an optional design structure of the above technical solution, the water model unit is made of plexiglass and has different thicknesses. The water model is made by stacking and combining multiple water model units of different or the same thickness.

[0009] As an optional design structure of the above technical solution, the first stacking positioning structure includes positioning posts, which are disposed on the top surface of the mold body.

[0010] As an optional design structure of the above technical solution, the second stacking positioning structure includes positioning holes, which are set on the bottom surface of the mold body and are matched with positioning posts.

[0011] As an optional design structure of the above technical solution, the top surface of the mold body is provided with two positioning posts. One of the positioning posts has a water injection hole along its axial direction, and the mold body has a first connecting hole inside. The two ends of the first connecting hole are respectively connected to the water injection hole and the water storage cavity. The other positioning post has an exhaust hole along its axial direction, and the mold body has a second connecting hole inside. The two ends of the second connecting hole are respectively connected to the exhaust hole and the water storage cavity.

[0012] As an optional design structure of the above technical solution, a first plug cap is provided in the water injection hole, and the first plug cap is equipped with a first sealing gasket; a second plug cap is provided in the vent hole, and the second plug cap is equipped with a second sealing gasket. Both the first plug cap and the second plug cap are made of radiation-proof plastic, and both the first sealing gasket and the second sealing gasket are made of radiation-proof rubber.

[0013] As an optional design structure of the above technical solution, the two positioning posts on the mold body are set at two opposite corners of the mold body.

[0014] As an optional design structure of the above technical solution, the mold body has cut edges on both opposite corners, the first connecting hole extends to one cut edge surface and is equipped with a first side plug; the second connecting hole extends to the other cut edge surface and is equipped with a second side plug.

[0015] As an optional design structure of the above technical solution, the bottom surface of the mold body is provided with an embedded mounting groove, which is connected to the water storage cavity and is provided with a sealing bottom cover.

[0016] As an optional design structure of the above technical solution, the side of the mold body is provided with a handle groove, and the top and side surfaces of the mold body are provided with calibration lines, which are cross-shaped engraving lines.

[0017] As an optional design structure of the above technical solution, one of the water model units is provided with an ionization chamber waterproof sleeve on the side of the model body, and the ionization chamber waterproof sleeve is threadedly connected to the ionization chamber.

[0018] The beneficial effects of this invention are as follows:

[0019] (1) The water phantom unit equipped with an ionization chamber can be stacked in different positions to control the distance from the radiation source to the ionization chamber and realize the detection of water absorbed dose at different measurement depths. This water phantom can be used to calibrate the water absorbed dose of about 2,000 radiotherapy medical accelerators in China, ensuring the accuracy and reliability of radiotherapy dose and improving the radiotherapy effect for cancer patients.

[0020] (2) Compared to a water tank, the water model is smaller in size, easier to fill and position, easier to measure and calibrate, and easier to transport.

[0021] (3) Compared with foreign water phantoms, this water phantom has a lower manufacturing cost, less impact from charge accumulation, shorter temperature equilibrium time, less impact on the ionization chamber, and more accurate measurement results. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the structure of the water model body in one embodiment of the present invention;

[0023] Figure 2 This is a schematic diagram of the first structure of the water model unit in one embodiment of the present invention;

[0024] Figure 3 This is a schematic diagram of a second structure of the water model unit in one embodiment of the present invention;

[0025] Figure 4 This is a schematic diagram of the third structure of the water model unit in one embodiment of the present invention;

[0026] Figure 5 This is a diagram showing the first usage state of the water model body in one embodiment of the present invention;

[0027] Figure 6 This is a diagram showing the second usage state of the water model body in one embodiment of the present invention;

[0028] Figure 7 This is a diagram showing the third usage state of the water model body in one embodiment of the present invention;

[0029] Figure 8 This is a diagram showing the fourth usage state of the water model body in one embodiment of the present invention.

[0030] In the diagram: 1-Water model unit; 2-Ionization chamber; 3-Model body; 4-Water storage cavity; 5-Water injection hole; 6-First connecting hole; 7-Vent hole; 8-Second connecting hole; 9-First plug cap; 10-First sealing gasket; 11-Second plug cap; 12-Second sealing gasket; 13-First side plug; 14-Second side plug; 15-Sealing bottom cover; 16-Handle groove; 17-Calibration line; 18-Ionization chamber waterproof sleeve. Detailed Implementation

[0031] Example

[0032] like Figures 1-8 As shown, this embodiment provides a water phantom for measuring water absorbed dose, comprising several stacked water phantom units 1, one of which is equipped with an ionization chamber 2. The water phantom units 1 have different thicknesses, and the water phantom is constructed by stacking and combining multiple water phantom units 1 of different or the same thickness. The length and width of each water phantom unit 1 are consistent, but their thicknesses differ.

[0033] like Figure 1 As shown, the water phantom unit 1 has thicknesses of 10 mm (theoretical correction factor of 0.929 for this study), 20 mm (theoretical correction factor of 0.963 for this study), 30 mm (theoretical correction factor of 0.975 for this study), 40 mm (theoretical correction factor of 0.981 for this study), 50 mm (theoretical correction factor of 0.985 for this study), and 60 mm (theoretical correction factor of 0.988 for this study). Users can select and use the appropriate unit according to their specific needs, thereby assembling water phantoms with thicknesses ranging from 1 to 23 cm for water absorbed dose measurement. The water phantom units 1 equipped with an ionization chamber 2 can be stacked in different positions to control the distance from the radiation source to the ionization chamber 2, enabling the detection of water absorbed dose at different measurement depths. This water phantom can be used to calibrate the water absorption dose of approximately 2,000 medical accelerators used in radiotherapy in China, ensuring the accuracy and reliability of radiotherapy doses and improving the radiotherapy effect for cancer patients.

[0034] Ionization chamber 2 is a detector that measures ionizing radiation using the ionization effect of ionizing radiation; it is also called an ionization chamber. Ionization chamber 2 consists of electrodes at different potentials and a medium between them. Ionizing radiation produces ion pairs in the medium. Under the influence of an electric field, positive and negative ions move towards the negative and positive electrodes, respectively, forming an ionizing current. Since the ionization charge is proportional to the radiation dose, the dose of ionizing radiation can be obtained by measuring this ionization charge. Typically, ionization chamber 2 is installed on a 20mm thick water phantom unit 1 to measure the absorbed dose of water.

[0035] Because the 10mm and 20mm thick water model unit 1 are too thin, they have certain differences. The 30mm, 40mm, 50mm, and 60mm thick water model unit 1 are structurally identical except for their thickness. Therefore, only three types of water model unit 1 will be introduced: the 20mm thick water model unit 1, the 10mm thick water model unit 1, and the 60mm thick water model unit 1.

[0036] like Figure 2As shown, the 20mm thick water model unit 1 includes a model body 3, a first plug cap 9, a second plug cap 11, a first sealing gasket 10, a second sealing gasket 12, a first side plug 13, a second side plug 14, a sealing bottom cover 15, and a waterproof sleeve 18 for the ionization chamber. The processing technology for the water storage cavity 4 in the model body 3 is as follows: an embedding groove corresponding to the shape of the sealing bottom cover 15 is milled 10mm from the edge of the model body 3 on the bottom surface. The depth of the embedding groove is 2mm. Then, a 20×20cm square groove is milled in the center of the model body 3, with the top surface of the groove 2mm from the top surface of the model body 3. The sealing bottom cover 15 is fitted with the embedding groove with a clearance, and then sealed with plexiglass adhesive. Handle grooves 16 are provided on both sides of the model body 3 for easy carrying and assistance in installing the water model. Calibration lines 17 are provided on the top and sides of the model body 3. These calibration lines 17 are cross-shaped markings used for calibrating the position of the ionization chamber 2. The water model unit 1 is made of acrylic glass (PMMA), the first plug 9 and the second plug 11 are both made of radiation-proof plastic, and the first sealing gasket 10 and the second sealing gasket 12 are both made of radiation-proof rubber.

[0037] Positioning posts are provided at two opposite corners of the mold body 3. One positioning post has a water injection hole 5 along its axial direction. The mold body 3 has a first connecting hole 6 inside, with both ends of the first connecting hole 6 communicating with the water injection hole 5 and the water storage cavity 4, respectively. The other positioning post has an vent hole 7 along its axial direction. The mold body 3 has a second connecting hole 8 inside, with both ends of the second connecting hole 8 communicating with the vent hole 7 and the water storage cavity 4, respectively. A first plug cap 9 is threaded to the water injection hole 5, and a second plug cap 11 is threaded to the vent hole 7. The first plug cap 9 is equipped with a first sealing gasket 10, and the second plug cap 11 is equipped with a second sealing gasket 12 to prevent ultrapure water leakage from the water storage cavity 4. After ultrapure water is injected into the water storage cavity 4, the water injection hole 5 and the vent hole 7 still leave a gap, which can remove air bubbles and reduce the impact of water expansion. Positioning holes are provided on the bottom surface of the mold body 3. The size and position of the positioning holes and the positioning posts are matched, so that each water mold unit 1 can be stacked together through the positioning cooperation of the positioning holes and the positioning posts. The water phantom has a simple structure, is easy and accurate to position, and is convenient to stack and combine for measuring water absorption dose.

[0038] Considering processing issues, a chamfer is provided at the diagonal of the positioning post. A first connecting hole 6 is provided on one chamfer surface, and a second connecting hole 8 is provided on the other chamfer surface. This allows the water injection hole 5 to communicate with the water storage chamber 4 through the first connecting hole 6, and the vent hole 7 to communicate with the water storage chamber 4 through the second connecting hole 8. A first side plug 13 is provided in the first connecting hole 6. The first side plug 13 is installed inside the first connecting hole 6, and the gap between the first connecting hole 6 and the first side plug 13 is sealed with plexiglass adhesive, keeping the end of the first connecting hole 6 sealed. A second side plug 14 is provided in the second connecting hole 8. The second side plug 14 is installed inside the second connecting hole 8, and the gap between the second connecting hole 8 and the second side plug 14 is sealed with plexiglass adhesive, keeping the end of the second connecting hole 8 sealed and preventing ultrapure water leakage. The mold body 3 has a through hole on one side for installing the ionization chamber waterproof sleeve 18. The ionization chamber waterproof sleeve 18 is inserted into the through hole and fixed with plexiglass glue. The ionization chamber waterproof sleeve 18 is threadedly connected to the ionization chamber 2, and the ionization chamber 2 extends into the water storage cavity 4.

[0039] The processing of the water model unit 1 includes: milling the upper surface of the model 3, leaving a positioning post with a height of 4mm and a diameter of Φ20mm; milling an embedding installation groove with the same shape as the bottom cover, using the upper surface of the model 3 as the reference surface, with a depth of 2mm; milling a 20cm×20cm square groove at the center of the embedding installation groove as a water storage cavity 4, with the top surface of the square groove 2mm from the top surface of the model 3; drilling positioning holes with a diameter of Φ20mm and a depth of 6mm at the position of the two positioning posts on the bottom surface of the model 3; drilling water injection holes 5 and vent holes 7 at the center of the two positioning posts to the center surface of the model 3; cutting the two diagonals at the positioning posts of the model 3, and then drilling a first connecting hole 6 and a second connecting hole 8 at the center of the two cut surfaces, so that the water injection hole 5 is connected to the water storage cavity 4 through the first connecting hole 6, and the vent hole 7 is connected to the water storage cavity 4 through the second connecting hole 8; and drilling through holes on the side of the model 3 that can mate with the ionization chamber waterproof sleeve 18.

[0040] like Figure 3 As shown, the 60mm thick water mold unit 1 includes a mold body 3, a first plug cap 9, a second plug cap 11, a first sealing gasket 10, a second sealing gasket 12, a first side plug 13, a second side plug 14, and a sealing bottom cover 15. The mold body 3 is 60mm thick. Compared with the 20mm thick water mold unit 1, the 30mm thick water mold unit 1, 40mm thick water mold unit 1, 50mm thick water mold unit 1, and 60mm thick water mold unit 1, as well as water mold unit 1 with a thickness of 60mm or more, have different sizes and shapes of the first side plug 13 and the second side plug 14. They do not have an ionization chamber waterproof sleeve 18 or a through hole that mates with the ionization chamber waterproof sleeve 18. Other structures are basically the same.

[0041] like Figure 4 As shown, the 10mm thick water mold body unit 1 includes a mold body 3, a first plug cap 9, a second plug cap 11, a first sealing gasket 10, a second sealing gasket 12, a first side plug 13, a second side plug 14, and a sealing bottom cover 15. The mold body 3 is 10mm thick. Compared with the 20mm thick water mold body unit 1 mentioned above, the 10mm thick water mold body unit 1 has different sizes and shapes for its first side plug 13 and second side plug 14. It does not have an ionization chamber waterproof sleeve 18 or a through hole that mates with the ionization chamber waterproof sleeve 18. Due to its thickness, it does not have a handle groove 16. Other structures are basically the same.

[0042] 60 A schematic diagram of the placement of the water phantom for measuring Co water absorption dose is shown below. Figure 5 and Figure 6 As shown, the distance SSD from the radiation source to the surface of the water phantom is 100 cm, the distance SCD from the radiation source to ionization chamber 2 is 105 cm, the radiation field size S on the surface of the water phantom is 10 cm × 10 cm, and the equivalent measurement depth D is 5 g / cm. 2 The theoretical correction factor for the water phantom in this study

[0043] A schematic diagram of the placement of the water phantom for accelerator photon beam water absorption dose measurement is shown below. Figure 7 and Figure 8 As shown, the distance SSD from the radiation source to the surface of the water phantom is 100 cm, the distance SCD from the radiation source to ionization chamber 2 is 110 cm, the radiation field size S on the surface of the water phantom is 10 cm × 10 cm, and the equivalent measurement depth D is 10 g / cm. 2 The theoretical correction factor for the water phantom in this study

[0044] It should be noted that with the development of processing technology, the container wall of water phantom unit 1 can be processed to be thinner, with better uniformity, higher dimensional accuracy, and better water equivalence. In addition, with breakthroughs in materials technology, materials that are cost-effective, easy to process, and whose density and radiation interaction are basically the same as water can be selected to make water phantom unit 1, so as to achieve zero disturbance of the radiation field by the water equivalent phantom.

[0045] Compared with the prior art, the present invention has the following advantages:

[0046] (1) This water phantom can replace the water tank for calibrating the water absorption dose of about 2,000 radiotherapy medical accelerators in China, ensuring the accuracy and reliability of the radiotherapy dose and improving the radiotherapy effect for cancer patients.

[0047] (2) Compared to a water tank, the water model is smaller in volume, without the surface tension ripples and evaporation effects of a water tank, making water filling and positioning operations convenient, easy to measure and calibrate, and easier to transport.

[0048] (3) Compared with foreign solid water, this water phantom has a lower manufacturing cost, less impact from charge accumulation, shorter temperature equilibrium time, less impact on ionization chamber 2, and more accurate measurement results.

[0049] In the description of this invention, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. They can refer to fixed connections, detachable connections, or integral connections; they can be mechanical or electrical connections; they can be direct connections or indirect connections through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art will understand the specific meanings of these terms in this invention. Furthermore, the specific features and structures described in the embodiments are included in at least one implementation method. Those skilled in the art can combine features from different implementation methods without contradiction. The scope of protection of this invention is not limited to the specific implementation methods described above. Based on the basic technical concept of this invention, implementation methods that can be conceived by those skilled in the art without creative effort are all within the scope of protection of this invention.

Claims

1. A water phantom for measuring water absorbed dosage, characterized in that, It includes several stacked water phantom units (1), and one of the water phantom units (1) is equipped with an ionization chamber (2). The water phantom unit (1) includes a phantom (3). The top of the phantom (3) is provided with a first stacking positioning structure, and the bottom of the phantom (3) is provided with a second stacking positioning structure. The interior of the phantom (3) is provided with a water storage cavity (4). Each water phantom unit (1) is stacked together through the cooperation of the first stacking positioning structure and the second stacking positioning structure. The cross-sectional size of the water storage cavity (4) in each water phantom unit (1) is the same. The first stacking positioning structure includes a positioning post, which is disposed on the top surface of the mold body (3); the second stacking positioning structure includes a positioning hole, which is disposed on the bottom surface of the mold body (3), and the positioning hole matches the positioning post. The top surface of the mold (3) is provided with two positioning posts. One of the positioning posts has a water injection hole (5) along its axial direction. The mold (3) has a first connecting hole (6) inside. The two ends of the first connecting hole (6) are connected to the water injection hole (5) and the water storage cavity (4) respectively. The other positioning post has an exhaust hole (7) along its axial direction. The mold (3) has a second connecting hole (8) inside. The two ends of the second connecting hole (8) are connected to the exhaust hole (7) and the water storage cavity (4) respectively. The two positioning pins on the mold body (3) are set on the two opposite corners of the mold body (3); both opposite corners of the mold body (3) are provided with tangled edges, the first connecting hole (6) extends to one tangled edge surface, and the first connecting hole (6) is provided with a first side plug (13); the second connecting hole (8) extends to the other tangled edge surface, and the second connecting hole (8) is provided with a second side plug (14).

2. The water phantom for measuring water absorption dosage according to claim 1, characterized in that, The water model unit (1) is made of plexiglass and has different thicknesses. The water model is made by stacking and combining multiple water model units (1) with different or the same thickness.

3. The water phantom for measuring water absorption dose according to claim 1, characterized in that, The water injection hole (5) is provided with a first plug cap (9), and the first plug cap (9) is equipped with a first sealing gasket (10); the vent hole (7) is provided with a second plug cap (11), and the second plug cap (11) is equipped with a second sealing gasket (12). The first plug cap (9) and the second plug cap (11) are both made of radiation-proof plastic, and the first sealing gasket (10) and the second sealing gasket (12) are both made of radiation-proof rubber.

4. The water phantom for measuring water absorption dosage according to claim 1, characterized in that, The bottom surface of the mold (3) is provided with an embedded installation groove, which is connected to the water storage cavity (4) and is provided with a sealing bottom cover (15).

5. The water phantom for measuring water absorption dosage according to claim 1, characterized in that, The side of the mold (3) is provided with a handle groove (16), and the top and side surfaces of the mold (3) are provided with calibration lines (17), which are "+" shaped engraving lines.

6. The water phantom for measuring water absorption dosage according to claim 1, characterized in that, One of the water model units (1) has an ionization chamber waterproof sleeve (18) on the side of the model (3), and the ionization chamber waterproof sleeve (18) is threadedly connected to the ionization chamber (2).

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