JP6919855B2 - Human body model dosimetry member, its manufacturing method and human body model dosimetry tool - Google Patents

Description

The present invention relates to a member for measuring a human model dose and a method for manufacturing the same.

With detectors that require electric circuits such as ionization chambers and semiconductor detectors, it is impossible to model human bodies equivalent to each organ on the measurement system, so the human body model phantom itself functions as a dosimeter. Dosimeters that can construct new systems are glass dosimeters, photostimulated luminescent dosimeters, dosimeters using brilliant phosphors, gel dosimeters, and thermoluminescent dosimeters.
Glass dosimeters utilize a phenomenon called radiophotoluminescence, but the only effective composition that exhibits this phenomenon is silver-activated phosphate glass. This silver-active phosphate glass has a problem that density control and molding are also difficult.
Similarly, effective compositions of a light-stimulated fluorescence dosimeter and a dosimeter using a luminescent phosphor are Al ₂ O ₃ with C added and BaFBr with Eu added. However, since these phosphors are greatly affected by optical fading, there is a problem that they are difficult to use as a human model phantom dosimeter.
The gel dosimeter is composed of tissue-equivalent substances, and it is possible to create a dosimeter equivalent to each organ by controlling the additives, but it cannot be used repeatedly and a large amount of waste is generated. There is a problem that it is necessary to control the atmosphere at the time of output and synthesis, it is difficult to keep the performance constant, and the cost is high. In particular, since expensive equipment such as a large-scale MRI or optical CT device is required for measurement, there is also a problem that it cannot be easily used.

In short, all of the components that can be used in the conventionally proposed anatomical phantoms are difficult to control and mold, are greatly affected by optical fading, cannot be used repeatedly, and generate a large amount of waste. It is difficult to keep the performance constant, the cost is high, and it is not easy to use. Therefore, the current situation is that there is a demand for the development of technology related to human model dosimetry that solves these problems. be.
Therefore, an object of the present invention is to manufacture a human model dosimetry member, which is easy to control and mold in density, is not affected by optical fading, can be used repeatedly, and can easily maintain constant manufacturing performance. The purpose is to provide a method and a mannequin dosimetry tool.

２．上記熱蛍光材料は、Ｃｒを熱蛍光材料全体中 １ 重量％以下の配合割合で含有することを特徴とする１記載の人体模型線量測定用部材。
３．Ａｌ_２Ｏ_３を主成分とする熱蛍光材料からなる人体模型線量測定用部材の製造方法であって、上記熱蛍光材料の構成成分を圧縮して熱蛍光材料の前駆体を製造する際の圧縮度を調整することにより、上記熱蛍光材料の嵩密度を所望の嵩密度とする、嵩密度調整工程を具備することを特徴とする人体模型線量測定用部材の製造方法。
４．人体模型と、該人体模型の所定部位に配設された線量測定用部材とを具備し、
上記線量測定用部材が、配設される人体模型の相当する人体の構成部位の電子密度と所定の関係を有する電子密度となるように嵩密度を調整してなる、１又は２記載の人体模型線量測定用部材である、人体模型線量測定具。 As a result of diligent studies to solve the above problems, the present inventors have found that alumina exhibiting thermal fluorescence characteristics behaves differently from the effective atomic number depending on its density, and as a result of further studies, under predetermined conditions. We have found that by controlling the bulk density, it is possible to make each part of the human body equivalent, and have completed the present invention.
That is, the present invention provides the following inventions.
1. 1. A human body model dosimetry member made of a thermofluorescent material containing _{Al 2} O _{3 as a main component.}
The bulk density of the thermofluorescent material is adjusted according to the following formula (1) so as to have an electron density having a predetermined relationship with the electron density of a desired constituent part among the constituent parts of the human body. Human body model Dosimetry member.

2. The human body model dosimetry member according to 1, wherein the thermofluorescent material contains Cr in a blending ratio of 1% by weight or less in the entire thermofluorescent material.
3. 3. A _{method for manufacturing a human model dosimetry member made of a thermofluorescent material containing Al 2} O ₃ as a main component, which is used to compress the components of the thermofluorescent material to produce a precursor of the thermofluorescent material. A method for manufacturing a member for measuring a human model dose, which comprises a bulk density adjusting step in which the bulk density of the thermofluorescent material is set to a desired bulk density by adjusting the degree.
4. A human body model and a dosimetry member arranged at a predetermined part of the human body model are provided.
The human body model according to 1 or 2, wherein the dose measuring member is adjusted in bulk density so as to have an electron density having a predetermined relationship with the electron density of a constituent part of the human body corresponding to the human body model to be arranged. A human model dose measuring tool that is a member for measuring dose.

The member for measuring the dose of a human model of the present invention is easy to control the density and mold, is not affected by optical fading, can be used repeatedly, and can easily have a constant manufacturing performance. In addition, there is an advantage that it can be constructed of inexpensive materials without using rare metals or the like.
Further, according to the method for manufacturing the human body model dosimetry member of the present invention, the above-mentioned human body model dosimetry member of the present invention can be obtained with stable performance, easily and easily.
Further, the human body model dosimetry tool of the present invention is useful in various radiation surveying fields as a human body equivalent model dosimeter.

FIG. 1A is a perspective view showing one embodiment of the human model dosimetry tool of the present invention, and FIG. 1B is a partially enlarged view thereof. FIG. 2 is a schematic explanatory view showing one form of dosimetry using the human model dosimetry tool of the present invention. FIG. 3 is a photograph (drawing substitute photograph) showing the thermal fluorescence measurement result of the human body model dosimetry member of the present invention having a bulk density of 50%. FIG. 4 is a photograph (drawing substitute photograph) showing the thermal fluorescence measurement result of the human body model dosimetry member of the present invention having a bulk density of 90%. FIG. 5 is a photograph (drawing substitute photograph) showing the thermal fluorescence measurement result of the human body model dosimetry member of the present invention having a bulk density of 80%. FIG. 6 is a photograph (drawing substitute photograph) showing the thermal fluorescence measurement result of the human body model dosimetry member of the present invention having a bulk density of 70%. FIG. 7 is a photograph (drawing substitute photograph) showing the thermal fluorescence measurement result of the human body model dosimetry member of the present invention having a bulk density of 60%. FIG. 8 is a graph showing the relationship between bulk density and thermal fluorescence characteristics. FIG. 9A is a photograph showing an example of a slab-shaped human body model (drawing substitute photograph), and FIG. 9B is a photograph showing the thermal fluorescence distribution (drawing substitute photograph).

Hereinafter, the present invention will be described in more detail.
The human body model dosimetry member of the present invention is a human body model dosimetry member made of a thermofluorescent _{material containing Al 2} O ₃ as a main component (hereinafter, may be referred to as "TLD" or "alumina TLD"). , The bulk density of the thermofluorescent material (hereinafter, may be referred to as "Bulk Density") is adjusted to an amount according to the relative electron density of the desired constituent part among the constituent parts of the human body according to the formula described later. It is characterized by that.
The details will be described below.

<Thermal fluorescent material>
(Principal component)
The thermofluorescent material has Al ₂ O ₃ as its main component. The crystal structure of Al ₂ O ₃ is not particularly limited.
(Sub-ingredient)
In the present invention, various sub-ingredients can be added to the main component without departing from the spirit of the present invention. In particular, it is preferable to use a luminescent component, and in the present invention, rare earth elements such as Cr, Ti, and Mn, transition metal elements, and the like can be preferably used.
(Quantity ratio)
When the above-mentioned luminescent component is used, the amount used is preferably 1% by weight or less in the whole thermofluorescent material, and more preferably 0.02 to 0.1% by weight. .. In particular, this quantity ratio relationship is in a preferable range when Cr is used as the light emitting component. Further, it is preferable that the luminescent component is dispersed and blended.
_{Even when a component other than the light emitting component such as SiO 2} or MgO is used as the sub component in addition to the light emitting material, the main component is 80% by weight or more in the total amount of the thermofluorescent material. It is preferable to contain it.
(form)
The shape of the thermofluorescent material is not particularly limited and may be various shapes, but basically it is preferably plate-shaped. Further, if it is a plate shape, its planar shape is not particularly limited, but it is preferable to have a cross-sectional shape of the liver as a planar shape when it is used in place of the human body part to be used, for example, the liver.
The thickness of the plate-shaped body is preferably 0.5 to 5 mm.

(The bulk density)
The bulk density of the thermofluorescent material in the present invention is adjusted so as to have an electron density having a predetermined relationship with the electron density of a desired constituent part among the constituent parts of the human body according to the following formula. In short, as is clear from the following formula, the bulk density of the desired human body is adjusted so that the relative electron density with respect to the electron density of the desired constituent part of the human body of the thermofluorescent material satisfies the following formula. It has the same blocking ability as the relative blocking ability of the constituent parts, and can be used as a dose meter member equivalent to the human body. In short, the member for measuring the dose of the human model of the present invention is formed by adjusting ε so that the following equation becomes equivalent to the relative electron density described later. Note that "equivalent" does not necessarily mean that the value of the relative electron density is exactly the same as the relative electron density of the constituent parts of the human body, and it can be said that it is usually equivalent if it is within ± 0.1. ..

(About the findings that found the above formula)
It was found as follows that it is suitable for the human body model dosimetry member to adjust the bulk density by such an equation.
That is, Compton scattering is dominant in the interaction between a photon and a substance of 0.1 MeV or more used in radiotherapy. Since the reaction cross section of Compton scattering depends on the electron density, it can be considered that the substances having the same electron density with respect to these photons have the same interaction, applied dose, and the like. If the ratio of the electron density to water is the relative electron density (Relative Electron Density) ρ _e / ρ _{e, w} , it is shown as follows.

The composition of various human body constituents is shown in ICRU44 (ICRU44 Appendix Body Tissue Composition), which is about ρ _e / ρ _{e, w} = 0.26 to 2.5, excluding low-density substances such as lungs. And ρ _e / ρ _{e, w} = about 0.9 to 2.5.
The relative electron densities of TLDs containing alumina (Al ₂ O ₃ ) as the main component (hereinafter referred to as alumina TLDs) ρ _{e, TLD} / ρ _{e, w} are approximated by the following equations.

From the above equation, it can be seen that the relative electron density of the alumina TLD is proportional to the material density. If the density of alumina TLD when the bulk density is not adjusted is ρ _{TLD, 0} = 3.70 g / cm ³ , then ρ _{e, TLD} / ρ _{e, w} = 3.27, which is larger than the relative electron density of the human body composition substance.
Assuming that the bulk density adjustment ratio is ε (≦ 1), the relative electron density of the alumina TLD with the bulk density adjusted is shown below.

Therefore, according to the above formula, it can be seen that the alumina TLD with a bulk density of 25 to 75% can adjust the relative electron density to about 0.9 to 2.5 and functions as a substance equivalent to the human body with respect to photons. , It can be seen that by adjusting the bulk density according to the above formula, it can be a member for dose measurement according to a part of the human body (each organ of internal organs, bone, etc.).

On the other hand, the interaction between charged particles and matter is defined by the amount of energy lost per unit distance called stopping power. The stopping power of the energy region used in particle therapy is well expressed by the Bethe-Bloch formula. It can be that the ratio of the stopping power and the stopping power of the water of a substance relative stopping power S / S _W expressed by the following equation.

The composition of the various body constituents are shown in _ICRU44, it is about S / S W = 0.26~1.8, excluding low-density materials such as pulmonary S / Sw = 0.9 to 1 It is about 8.8.
TLD mainly composed of alumina (Al ₂ O ₃₎ (hereinafter, sometimes referred to as "alumina TLD") relative stopping power S _{TLD /} S _W of is approximated by the following equation.

である。上式を計算すると以下のようになる。 here

Is. The above formula is calculated as follows.

From this equation, it can be seen that the relative stopping power of the alumina TLD is proportional to the material density (that is, the values shown in Equation 9 correspond to the relative stopping power in Table 1 described later). The relative electron density greater than _{S TLD} / _{S w} = 3.06 next body composition material when the density of the alumina TLD when not adjusted bulk density and _{ρ TLD, 0 = 3.70g / cm} 3.
On the other hand, assuming that the bulk density adjustment ratio is ε (≦ 1), the relative electron density of the alumina TLD whose bulk density is adjusted is shown below.

この式より嵩密度の調整により相対阻止能を調整することができることも明らかである。これにより、嵩密度30〜60%のアルミナTLDは相対阻止能を０．９〜１．８程度に調整することができ、荷電粒子に対して人体等価な物質として機能する線量測定用部材となり得ることがわかる。
表１にアルミナTLDと人体構成物質の相対電子密度、相対阻止能の例を示す。

From this equation, it is also clear that the relative stopping power can be adjusted by adjusting the bulk density. As a result, the alumina TLD with a bulk density of 30 to 60% can adjust the relative stopping power to about 0.9 to 1.8, and can be a dosimetry member that functions as a substance equivalent to the human body with respect to charged particles. You can see that.
Table 1 shows examples of relative electron densities and relative stopping powers of alumina TLDs and human body constituents.

(Production method)
In the human model dosimetry member of the present invention, the bulk density of the thermofluorescent material is adjusted by adjusting the compressibility in the process of mixing and compressing the constituent components, or by adjusting the type and amount of binder added to the constituent components. It can be obtained by performing a bulk density adjusting step for adjusting the addition.
Hereinafter, the method of adjusting the compression ratio will be described in detail.
The bulk density adjusting step can be carried out by mixing other components such as alumina powder and chromium powder, which are raw materials for the thermofluorescent material, and changing the compression ratio at the time of compression. The bulk density can also be adjusted by adjusting the average particle size of the alumina powder and chromium powder used.
Specifically, alumina powder and chromium powder are usually used as constituents of alumina-based ceramics, and the bulk density can be adjusted by appropriately adjusting the compressibility. At this time, if the compressibility is lowered, a thermofluorescent material having a low bulk density can be obtained, and if it is increased, a thermofluorescent material having a high bulk density can be obtained.
Here, the "compressibility" refers to the compression of the powder aggregate inside the container by applying pressure from one direction of the container when the volume in the state where the powder is simply charged into the container (initial state) is 100%. The volume of the case was compared with the volume in the initial state, and the reduction rate was used as the compression rate.
Further, the compression method and the like are the same as those for producing a normal ceramic material, and other steps of this step can be performed in the same manner as for a normal ceramic material.

(Usage / action / effect)
Since the member for measuring the dose of the human body model of the present invention uses the thermofluorescent material whose bulk density is adjusted as described above, the human body model dose is measured at a desired measurement location in the same manner as a dosimeter made of a normal thermofluorescent material. After installing the members and exposing them to a predetermined measurement time, they are collected and collected using the devices described in JP-A-2014-288913 and the like, and the same publications [0032] to [0039]. ] And the like, it can be used by detecting thermal fluorescence and measuring the dose by comparing the detected thermal fluorescence with the calibration curve.
According to the human body model dosimetry member of the present invention, the material can be used as an equivalent material for each component of the human body, so that the spatial resolution is sufficient as in the case of arranging a large number of dosimeters on the human body phantom for measurement. In addition, since the radiation field is disturbed by the scattering and absorption of the installed dosimeter itself, there is no problem that the dose distribution is different from the original dose distribution inside the human body.
In addition, like ordinary glass dosimeters, photostimulated luminescence dosimeters, dosimeters using brilliant phosphors, gel dosimeters, conventional thermoluminescent dosimeters, etc., density control and molding are easy, and light It is not significantly affected by fading, can be used repeatedly, has a small amount of waste, and is easy to maintain constant performance. Further, since no expensive material is used as the material, it can be obtained at low cost and can be easily used.
It can also be used in the human model dosimetry tool of the present invention.
That is, as shown in FIGS. 1A and 1B, in the human body model dosimetry tool 1 including the human body model 10 and the dosimetry member 20 arranged at a predetermined portion of the human body model 10. As the dosimetry member 20, the above-mentioned human model dose measurement member of the present invention is used. At this time, all of the dosimetry member 20 can be composed of the human body model dosimetry member of the present invention, and as shown in FIG. 1 (b), a portion corresponding to bone and a portion corresponding to fat. , It can be divided into parts corresponding to soft tissues, and can be configured by using the human body model dosimetry member of the present invention (simply referred to as "member" in the figure) equivalent to each part.
Then, in order to measure the dose using the human model dosimetry tool 1 of the present invention, as shown in FIG. 2, the human model dosimetry tool 1 of the present invention is first irradiated with a predetermined radiation. Next, the human body model dosimetry member 20 of the present invention is taken out from this human body model dosimetry tool, and thermal fluorescence is measured using a wavelength discrimination type CCD camera or the like while heating with a heater. Then, the measurement can be performed by calculating the amount of light distribution for each wavelength. When only the bulk density is set to be different depending on the corresponding part of the human body in the member like the human body model dosimetry member of the present embodiment, the bulk density is different for each, so the different parts. The dose distribution can be obtained from the dose response curve for each case. When the luminescent components are different, a dose response curve can be created for each wavelength and the dose distribution can be obtained.

Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples, but the present invention is not limited thereto.

〔Example〕
A plate-shaped member was prepared with the composition shown in the table below, with a bulk density of 50% and a density of 1.85 g / cm ³ (assuming a member capable of obtaining a relative electron density and a relative stopping power equivalent to the mandible of the human body). In the process of producing the element, plate formation and density control were examined, and the thermal fluorescence characteristics and deliquescent property of the obtained member were examined. The results are shown in Table 2.
Each item was judged as follows.
Plate-shaped;
When it was formed into a plate shape in the same manner as ordinary ceramics, it was visually judged according to the following criteria.
⊚: Flat plate shape without distortion.
◯: There is some distortion, but it is almost flat.
Δ: Slight distortion is seen.
×: There is a lot of distortion.
Density control;
When the density was controlled to the bulk density, it was determined by the following criteria whether the density could be controlled to a desired bulk density.
⊚: Density could be controlled with a desired bulk density ◯: Density could be controlled with almost a desired bulk density Δ: Some deviation from the desired bulk density.
X: Density could not be controlled.
Thermal fluorescence characteristics;
The result of measuring the thermal fluorescence was judged according to the following criteria.
⊚: Thermal fluorescence could be detected with high resolution.
◯: Thermal fluorescence could be detected.
Δ: Thermal fluorescence was almost detected ×: Thermal fluorescence could not be detected very much.
Deliquescent;
Judgment was made according to the following criteria by observing the state when immersed in water.
⊚: No deliquescent was observed as a result of immersion for 24 hours.
◯: As a result of soaking for 24 hours, some deliquescent was observed.
Δ: Deliquescent was observed as a result of immersion for 24 hours.
X: Deliquescent was observed after immersion for 10 hours.

As is clear from the results shown in Table 2, it is clear that the human body model dosimetry member of the present invention, which is obtained by adding Cr to _{Al 2} O _{3, is excellent in all items.}
The relative stopping power of the obtained alumina TLD is as shown in Table 1, which corresponds to the mandibular bone of the human body.
When four alumina TLDs were stacked and irradiated with 6 MV X-rays for 2 Gy and the thermal fluorescence characteristics were measured, the alumina TLDs in the uppermost layer and the alumina TLDs in the lowermost layer had almost the same thermal fluorescence characteristics as the results of the human body simulation. Indicated. From this, it can be seen that it is useful as a dosimeter member for a human body model.
Further, the human body model dosimetry member of the present invention was prepared by adding Cr to _{Al 2} O ₃ with the bulk density set to 90%, 80%, 70%, and 60%. The obtained alumina TLDs were similarly stacked on top of each other and irradiated with 2 Gy, and the thermal fluorescence characteristics were measured. Indicated.
These results are shown in FIGS. 3-7.
Although only examples with a bulk density of up to 50% are given here, those having a lower bulk density, for example, those having a bulk density of 40 to 10% shown in Table 1 can also be produced.
In addition, the relative thermal fluorescence intensities for alumina TLDs having different bulk densities were measured according to a conventional method. The result is shown in FIG. As is clear from FIG. 8, the relative thermal fluorescence intensity also decreases as the Bulk Density decreases. However, all Bulk Densities showed sufficient strength for dosimetry.
Further, an Armin TLD having a bulk density of 50% was used to prepare a slab-shaped human body model (cross section of the pelvis portion of the human body) shown in FIG. 9 (a). Then, 2 Gy irradiation was performed under the above conditions, and thermal fluorescence was measured. The thermofluorescent image is shown in FIG. 9 (b). It can be seen that an image similar to a thermofluorescent image of a cross section of the pelvis of the human body has been obtained. From this, it can be seen that if the members for human body model dosimetry having different bulk densities are created and the dose response curves are created for each member, the dose distribution can be converted.

Claims (4)

A human body model dosimetry member made of a thermofluorescent material containing _{Al 2} O _{3 as a main component.}
The adjustment ratio of the bulk density of the thermofluorescent material satisfies the following formula (1), and the relative electron densities ρ _e / ρ _{e, w} of the desired constituent parts of the human body with respect to water and the above thermal phosphors A member for measuring a human body model dose, characterized in that the relative electron densities ρ _{e and TLD} / ρ _{e, w} with respect to water are adjusted to be equivalent.

The member for measuring a human model dose according to claim 1, wherein the thermofluorescent material contains Cr in a blending ratio of 1% by weight or less in the entire thermofluorescent material. The method for manufacturing a member for measuring a human model dose according to claim 1.
A bulk density adjusting step is performed in which the bulk density of the thermofluorescent material is set to a desired bulk density by adjusting the degree of compression when the components of the thermofluorescent material are compressed to produce a precursor of the thermofluorescent material. A method for manufacturing a member for measuring a human model dose, which is characterized by being provided. A human body model and a dosimetry member arranged at a predetermined part of the human body model are provided.
The first or second claim, wherein the dose measuring member is adjusted in bulk density so as to have an electron density having a predetermined relationship with the electron density of a constituent part of the human body corresponding to the arranged human body model. A member for measuring the dose of a human model,
Human model dosimetry tool.

Images