DE2650384A1 - Geometrically reduced individual irregular compensator - for radiation therapy with high energy photons - Google Patents

Abstract

Method is provided for mfg. a geometrically reduced individual irregular compensator to be placed at a distance from a patient in the path of radiation, for improving dose distribution in therapeutical irradiation of irregular body surfaces with high-energy photons, with scanning of the body surface and simultaneous transmission to means for shaping the compensator. To place the compensator at the radiation source, a precise negative or positive of the compensator is formed with lateral geometrical correction and radial absorption correction. A material of high at.no. and high density and with sufficient strength and high deformation capacity is then supplied for the positive, to minimise its thickness so that it can then be placed at a radiation source. Pref. the compensation is made of an alloy comprising 50%Bi, 26.7%Pb, 13.3%Sn and 10%Cd,. Pref. the Schmidt corrector is made from polystyrene and plexiglass.

Description

Method and device for

Manufacture of compensators for radiation therapy The present The invention relates to a method and a device for producing a spaced-apart Geometrically reduced, individual to be arranged by a patient in the beam path Compensator for improving the dose distribution during therapeutic radiation irregular body surfaces of a patient, especially with high-energy Photons, being over in the vicinity of the patient lying on a table arranged means a scan of the relevant body surface and simultaneously A transfer of the resulting values to the design of the expansion joint necessary means takes place.

A prerequisite for successful radiation therapy in one Patients is to achieve a high dose distribution that is as uniform as possible in every volume to be irradiated while at the same time optimally protecting the surrounding area Tissue. An irregular body surface in the radiation entry field can occur in particular Irradiations in the head / neck area and deviations in the case of extensive irradiation of the desired dose homogeneity of an order of magnitude of up to 40%.

To compensate for this caused by irregular body contours irregular dose distribution, it is known special, individual compensators to bring into the beam path.

So far, expansion joints have been made from various homogeneous materials (e.g. wax, plexiglass, copper, lead) using different processes for recording the irregular body contours and the subsequent design of the individual expansion joints have been applied.

Especially in Anglo-American countries there has also been another Another method was enforced, namely the expansion joints from many individual metal cylinders (Ellis expansion joints).

The disadvantage of all of the above methods is particularly in this too see that the manufacture of a compensator takes a lot of time and resources which makes them unsuitable for routine radiotherapy are.

For this reason, it has recently been switched to by means of a suitable device simultaneously with the scanning of the body surface a negative for a laterally reduced compensator made of tissue-equivalent material to accomplish.

Compensators produced in this way are disadvantageous in that they are made of tissue-equivalent material, i.e.

low atomic number e.g. consist of wax and thus a large, Require a thickness (up to 15 cm) appropriate to the missing fabric layer, as well as high electron contamination of the photon bundle and thus a high surface dose load cause. It should also be noted that there is a risk of overcompensation or undercompensation in parts of the radiation field at different distances from the central ray with missing Tissue layers of different thicknesses and at different depths in the tissue decreasing atomic number increases.

The present invention is therefore based on the object To specify a method and a device for producing a compensator, which is relatively easy and quick to make, and compared to the known embodiments ensures a much better dose distribution. According to the invention The object is achieved in that for the purpose of arranging the compensator at the radiation source Using the appropriately designed means, an exact, laterally geometrically corrected and radially absorption-corrected negative or positive of the compensator becomes, and that for the positive to minimize its only then without further ado the Arrangement at a radiation source allowing thickness a material of high atomic number and high density, as well as sufficient strength and easy formability will.

Further advantages of the present invention will become apparent from the following Description of procedural peculiarities and implementation conditions a simple example explained in more detail: On one with high-energy photons working radiation therapy device, brackets are provided on the radiator head, in the well-known wedge filter inserted for isodose formation or so-called absorber satellites to protect certain areas of the body that are in the radiation field can be. In addition to these devices is now the invention manufactured compensator also held on the radiator head, whereby the removal of the body surface is about 30 cm. This means that it has a flat shape must have, and to be sure to insert it into the existing one respectively.

to allow extended bracket. This is also due to this requirement it is therefore necessary to use a material that has higher absorption properties as tissue equivalent material. It has proven to be in this context Proven to be beneficial, for the compensator a so-called, already for the manufacture the absorber satellites used Lipowitz metal (alloy of about 50 ffi Bi, 26.7% Pb, 13.3% Sn and 10 fo Cd) should be used. This material stands out due to a high atomic number and a low melting point, as well as easy malleability off, that is, it can be produced very well in a relatively simple and inexpensive manner Negative molds can be cast into a compensator. For the negative forms, on the one hand a thermally and / or mechanically easily machinable, fine-pored, dense and heat-resistant (up to 800 C dimensionally stable) polystyrene hard foam part I (see Fig. 3a) used, each completed by a cast cover II (see Fig. 3a) is, through which it is ensured that all compensators III, (see Fig. 3b) the have the same edge design and thus easily in a frame part IV (see Fig. 3c, 3d) can be accommodated e.g. made of Plexiglas, which can be inserted into the on the radiator head housed bracket can be used.

The following factors must be taken into account when manufacturing the expansion joint: Due to the arrangement of the compensator on the radiator head, this is necessary corresponding to the divergence that is present in the beam path and caused by the distance to reduce laterally. In addition, since a material is used that has a higher Has absorption coefficients than the fabric, a radial correction is also made, i.e. a reduction is necessary. This correction is then dependent on other factors influenced by device-specific parameters and dosimetric requirements of the user, or radiation-physical conditions, as well as the thickness of the missing tissue that needs to be compensated for.

A produced in this way, i.e. lateral-geometrically and radially with respect to the absorption of exactly corrected Kom sator causes the real dose distribution if at all, it deviates only slightly from the ideal dose distribution.

To manufacture such a compensator, e.g.

the device according to the invention described below is used will.

In the vicinity of a patient B on a table A. a tripod that can be pivoted through an angle (900 or 2700) is positioned in such a way that that a scan of the body surface to be irradiated by means of one held on a tripod and hung in the focus of the virtual radiation source Device and a transfer to a work station for forming a negative form is possible. For this purpose, a boom 2 is arranged on the stand 1. To the Cantilever 2, a ball joint bushing 3 is held in the focus of the virtual radiation source, in which one arm is held adjustable in height 4 x in the direction of the double arrow, in such a way that it spatially in every direction (indicated by the angles) is deflectable.

As can be seen from FIG. 2, the arm 4 is a toothed rack 5 positively connected, on which a gear Z1 of a gear pair 6 moves. With this gear Z1, another gear Z2 is rigidly connected with a second rack 7 is in engagement, which with a second arm 8 in a form-fitting manner is connected to which a position-stabilized by a spring 9, mechanical or electrical means 12 (milling cutter or filament) for making the most essential Part I of the negative mold is arranged.

This part I of the negative mold is made from a rigid polystyrene foam formed, which turns out to be correspondingly thick and broad, as well as deep and on the radiation field centered plate I on one in the direction of the double arrow y on the stand 1 over a Boom 10 adjustable in height, rotatable for the purpose of alignment according to the double arrow z Bracket 11 (see Figs. 1 and 3) is located.

To move the means 12, the gear pair 6 is with one leg a U-shaped bracket 13, the other leg of which is a sensing element 14 for the body surface to be irradiated.

The transmission ratio between the two toothed wheels Z1 and Z2 is, as mentioned, the size of the to be irradiated due to the material of the compensator Field, the dosage depth and the thickness of the layer to be compensated. In the case of changing physical radiation conditions, it is therefore necessary to also to change the transmission ratio. This can be done either in stages (using a switchable transmission) or continuously.

The advantage of the simple measures and features according to the invention compared to the known compensators, it can be seen in particular that the Compensators can be manufactured very easily and yet very precisely, and thus are particularly suitable for routine radiotherapy, namely can practically all irradiation cases with photon standing fields at any collimator rotation angle be treated.

- patent claims -

Claims (1)

Claims 1.) A method for producing one at a distance of Geometrically reduced, individual, to be arranged in the beam path of a patient irregular compensator for improving dose distribution in therapeutic Irradiation of irregular body surfaces of a patient with high-energy Photons, being over in the vicinity of the patient lying on a table arranged means a scan of the relevant body surface and simultaneously a transfer of the resulting values to the design of the compensator necessary means takes place, characterized in that for the purpose of arranging the compensator at the radiation source via the appropriately designed means an exact, lateral geometrically corrected and radial absorption corrected negative or positive of the compensator is formed, and that for the positive to minimize its only then easily a material that allows the arrangement at a radiation source of high atomic number and high density as well as sufficient strength and lighter Malleability is used. 2.) The method according to claim 1, characterized in that for the Production of the negative is a two-part process that allows a thin positive to be cast Form is used, the one hand from one of a part of the means thermally and / or mechanically easily malleable, fine-pored, dense and heat-resistant Rigid polystyrene foam and, on the other hand, made of a suitably preformed part made of Plexiglas is formed. 30) Method according to claim 1 or 2, characterized in that the negative or positive to correct the angle-dependent, systematic aberrations In addition, a suitable concave shape is given, which is opposite that of the body surface simulated surface lies. 4.) The method according to claim 1 or one of the following, characterized in, that the material for the compensator is a so-called Lipowitz metal from about 50% egg, 26.7 # Pb, 13.3 # Sn and 10% Cd is used. 5.) Device for performing the method according to claim 1, wherein a tripod is provided near the patient on which the virtual Radiation source for scanning the body surface and for shaping of the compensator are kept deflectable, thereby characterized in that for the correction of the device-specific Parameters and dosimetric desires of the user or radiation physics Conditions as well as the thickness of the missing and thus to be compensated Tissue as well as the material of the compensator (III) standing absorption between corresponding to the scanning means (13-14) and the shaping means (8-12) influenceable correction element (5 - 7) is provided. 6.) Device according to claim 5, characterized in that the correction element (5 - 7) can be set continuously or in steps. 70) Device according to claims 1 - 5, characterized in that that the #Means (4-14) in the focus of the virtual radiation source via a pierced Ball joint (3) are held, whereby changes in length to adapt to different Irradiation distances and exact lateral scanning movements are possible, and that the correction ratios are adjustable. a 8.) Device according to claims 5-7, characterized in that that a concentric-parallel guide for essentially consisting of a tripod (1), a scanning bracket (13) and a cutting device (12) existing middle is provided, and that the cutting device (12) consists of a high-speed electric motor and a milling head moved therefrom, the shape and the radius of the milling cutter is adapted to the geometric relationships of the scanning element. 9.) Device according to claims 5-8, characterized in that that the correction by rolling a first gear (Z1) on one on the tripod (1) attached first rack (5) and driving one by one or more second gear (s) connected to the first gear (s) (Z2) moved on the cutting device (12) attached to the second rack (7) is realized, wherein the correction ratio is given by the tooth difference. 100) Device according to one of claims 6 - 9, characterized in that that the scanning element (14) is parallel to the virtual central beam on the center of the field centered by a mechanical locking device at an angle of Oo is.