ES2571056B1 - Multilayer bolus for radiotherapy - Google Patents

Abstract

Multilayer bolus for radiotherapy. # The invention describes a multilayer bolus (1) for radiotherapy comprising: a lower sheet (2); a permeable top sheet (3); and an intermediate sheet (4), enclosed between the lower sheet (2) and the upper sheet (3), which contains a superabsorbent polymer. Thus, it is sufficient for the user to provide water to the bolus (1) so that it is trapped in the superabsorbent polymer deposited in the intermediate sheet (4), the bolus (1) adopting a thickness suitable for use.

Description

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DESCRIPTION

Multilayer bolus for radiotherapy OBJECT OF THE INVENTION

The present invention belongs to the field of medicine, and more particularly to the field of radiotherapy.

The object of the present invention is a novel bolus for radiotherapy manufactured from a superabsorbent material immobilized between two sheets, at least one of which is permeable.

BACKGROUND OF THE INVENTION

Radiation therapy is based on the application of radiation to a tumor to destroy the malignant cells, preventing them from growing and reproducing. The radiation crosses the patient's body a certain distance, exerting most of its effect at a depth under the patient's skin that depends on the penetrability of each specific radiation, so that its effect decreases exponentially from that depth. However, sometimes the tumor to be treated is at a depth less than that where the effect of radiation is greater, for example on the patient's own skin or very close to it. In these cases, the conventional use of radiation barely has an effect on the tumor area.

To solve this problem, it is known the interposition between the radiation source and the skin of a layer of material whose radiation absorption capacity is similar to that of the human body. If the thickness of the layer is calculated properly, it is possible to place the area of greatest radiation on the patient's skin. This element receives in the field of medicine the name "bolus." In addition to being adaptable to the patient's skin shape, a bolus usually has a density similar to that of the human body, that is, water. The object is that its radiation absorption capacity is similar to that of the human body, thus acting on radiation as if it were part of the patient's body and allowing the calculation of the absorbed dose with the required accuracy, however, this does not It is essential and bolus are based on high density materials, such as those based on silicones or metal meshes.

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Various types of bolus are currently known, among which the following can be mentioned: gel-based bolus, such as the so-called superflab, superflex and elastogel; moldable bolus based primarily on thermoplastic materials, such as so-called superstuff, aquaplast and polycaprolactone-based materials; and bolus based on surgical wax, paraffins and medical grade silicones, such as those based on polyvinyl siloxane.

Although all these bolus solve the problem, the high manufacturing cost of most of them prevents their widespread use, due to which the use of less precise and exact solutions based on the use of gauze or wet loaves is frequent, which They have the serious disadvantage of not guaranteeing the thickness of bolus equivalent to water and even that this thickness has important variations. In addition, another drawback of known boluses is that it is often not possible to adapt their size to that of the area of the patient where they are to be used.

DESCRIPTION OF THE INVENTION

The inventors of the present invention have developed a novel multilayer bolus for radiotherapy that includes a superabsorbent polymer. The superabsorbent polymers (SAP, Super Absorbent Polymer) were developed in the 60s of the last century during the search for materials for water retention. Some of these materials have the property of being able to absorb 300 to 1000 times their weight in water. Because of this, they have been used successfully in gardening, baby combs, sanitary napkins, artificial snowmaking and fire water compounds, among others. Some examples of superabsorbent polymers that can be used in the present invention are: copolymer of polyacrylamide, copolymer of maleic ethylene anhydride, cross-linked carboxymethylcellulose, copolymers of polyvinyl alcohol, crosslinked polyethylene oxide, copolymer of polyacrylonitrile polyethylene sodium grafted polyacrylonitrile . Of all of them, sodium polyacrylate is the most commonly used today.

The multilayer bolus for radiotherapy of the invention essentially comprises the following elements: a lower sheet, a permeable upper sheet, and an intermediate sheet, enclosed between the lower sheet and the upper sheet, which contains a superabsorbent polymer. Thus, to use this bolus, the user only has to provide water, for example by immersing the bolus in a water tank for a controlled time or adding a known amount of water. Water passes through the top sheet

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permeable and absorbed by the superabsorbent polymer contained in the intermediate sheet. As a consequence, the intermediate sheet swells and the overall thickness of the bolus increases dramatically. Once swollen, the bolus of the invention is essentially formed by water, and therefore its behavior against radiation is similar to that of the human body, thus guaranteeing a dosimetric calculation with the accuracy required in the clinical use.

According to a preferred embodiment of the invention, the intermediate sheet is made of a porous material that houses the superabsorbent material in the form of dust particles normally distributed homogeneously. For example, the diameter of the dust particles of the superabsorbent polymer may be between 10 microns and 1000 microns.

According to another preferred embodiment of the invention, the lower, upper, and intermediate sheets are made of a textile material. Furthermore, preferably the outer face of the lower base sheet comprises an adhesive to allow its fixation to the patient's skin. In another preferred embodiment, the bottom sheet is impermeable to prevent the patient's skin from getting wet when the bolus of the invention is applied, unlike what happens when gauze or wet wipes are used.

An important advantage of the bolus of the invention is that its thickness is variable depending on the amount of water that is administered. In fact, preferably the thickness of the bolus of the invention is between 3 mm and 15 mm when swollen with water. That is, if only a small amount of water is applied, for example by means of a graduated syringe, the thickness adopted by the bolus is approximately 3 mm. On the contrary, if the intermediate sheet is saturated with water by introducing the bolus into a bucket of water, the thickness of the bolus will be approximately 15 mm. Note that this range of thicknesses is useful for the use of this bolus, but by increasing or decreasing the amount of sodium polyacrylate deposited in the intermediate sheet, both values may be modified. In this way, by controlling the amount of water that is applied, it is possible to control the final thickness of the bolus to adjust it to each specific application. In addition, before the application of water by the end user, the bolus has a very small thickness, which is advantageous for more compact storage and transport.

Another advantage of this bolus is that it has a manufacturing and development cost much lower than that of the bolus currently known, since the manufacturing technology currently existing in the honeycomb and sanitary napkins industry can be used.

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Price of superabsorbent material is highly competitive.

Another added advantage is the elimination of artefacts in the simulation TAC, so that the use of plastics or polysiloxanes that sometimes do not have a simple electronic HU-density response is avoided. Regarding the bolus made in waxes, thermoplastic material or silicones, the main advantage is the rapidity of preparation.

BRIEF DESCRIPTION OF THE FIGURES

Fig. 1 shows a scheme of the bolus of the invention where the different layers that form it are appreciated.

Fig. 2 shows a CT image that corresponds to the use of the bolus on a maniqul.

Fig. 3 shows a graph of the yield of the irradiated dose according to the depth. PREFERRED EMBODIMENT OF THE INVENTION

An example of a multilayer bolus (1) for radiotherapy according to the present invention is described below with reference to the attached figures.

Fig. 1 shows a diagram of the bolus (1) where the different layers that compose it are appreciated: the lower sheet (2), the upper sheet (3) and the intermediate sheet (4). The intermediate sheet (4), enclosed between the lower sheet (2) and the upper sheet (3), is made of a porous material where sodium powder polyacrylate is homogeneously deposited. The upper sheet (3) is permeable to allow water to enter the bolus (1). The bottom sheet (2) is in this example waterproof. Furthermore, to allow the bolus (1) to be fixed to the skin of a patient, the outer face of the lower sheet (2) comprises an adhesive, for example similar to that of a tape.

To use this bolus (1), firstly a piece of bolus (1) is cut with scissors with a size and shape appropriate to the area of the patient where it will be used. Next, the amount of water that corresponds to the thickness that will be needed is applied taking into account the amount of sodium polyacrylate contained in the intermediate sheet (4). For example, in this particular example, sufficient water can be applied to make the bolus (1) acquire a thickness of 10 mm. Finally, once swollen

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up to the desired thickness, the bolus (1) adheres to the patient's skin in the area where he is going to undergo radiotherapy using the adhesive on the outer face of the lower sheet (2). Since the bottom sheet (2) is waterproof and also the water contained in the intermediate sheet (4) is gelled, the patient's skin does not get wet. The gelation obtained by means of sodium polyacrylate guarantees the thickness of water during treatment, and the bolus can be reused for several sessions or a single use can be used for convenience.

Figs. 2 and 3 show the effect of the use of this new bolus (1) when radiation is applied to a maniqul (100) that simulates the behavior of human tissue. The intensity of the radiation received is shown schematically in Fig. 10 2, showing that the

The innermost contour representing the maximum intensity of radiation is centered on the surface of the maniqul (100) that simulates the patient's skin. On the other hand, Fig. 3 shows a graph showing how the use of bolus (1) displaces the depth of the point where the maximum intensity of radiation takes place to an area closer to the skin 15 of the patient.

Claims (8)

5 10 fifteen twenty 25 30 ES 2 571 056 A1 1. Bolus (1) multilayer for radiotherapy, characterized in that it comprises: - a lower sheet (2); - a permeable top sheet (3); Y - an intermediate sheet (4), enclosed between the lower sheet (2) and the upper sheet (3), which contains a superabsorbent polymer. 2. Bolus (1) according to claim 1, wherein the lower (2), upper (3) and intermediate (4) sheets are made of a textile material. 3. Bolus (1) according to any of the preceding claims, wherein the intermediate sheet (4) is made of a porous material that houses the superabsorbent polymer in the form of dust particles. 4. Bolus (1) according to claim 3, wherein the diameter of the dust particles of the superabsorbent polymer is between 10 microns and 1000 microns. 5. Bolus (1) according to any of the preceding claims, wherein the outer face of the lower sheet (2) comprises an adhesive to allow its fixation to the patient's skin. 6. Bolus (1) according to any of the preceding claims, wherein the bottom sheet (2) is waterproof. 7. Bolus (1) according to any of the preceding claims, which is between 3 mm and 15 mm thick when swollen with water. 8. Bolus (1) according to any of the preceding claims, wherein the superabsorbent polymer is chosen from: polyacrylamide copolymer, maleic ethylene anhydride copolymer, crosslinked polymethylcellulose, polyvinyl alcohol copolymers, crosslinked polyethylene oxide, polyacrylonitrile copolymer grafted starch, and sodium polyacrylate.