DE202004007286U1 - Transparent acrylic plastic jig used in three-dimensional x-ray diagnosis procedure, holds perforated plastic discs into which x-ray opaque beads are inserted - Google Patents

Abstract

The support panel (100) is mounted on three adjustment screws (102) a casing (105) with plastic screws (104) is fastened onto it. (105) contains and clamps plastic discs (106) of the same diameter and thickness. Each has an upper groove (201), allowing (106) to be fastened with a safety strap (109). Into holes made in (106), x-ray opaque beads are inserted, as objects to assist measurement.

Description

The invention relates to a plexiglass seed phantom for image-based evaluation methods in X-ray diagnostics.

Prostate cancer is after bronchial carcinoma the second most common Cause of death from tumors for the man in Central Europe Range, with the incidence increasing slightly in recent years Shows increase. Dependent come from the tumor stage for the treatment of prostate cancer in different options Question. Percutaneous is an alternative to prostatectomy Radiation therapy or brachytherapy. Here is through high-energy Radiation destroys the tumor tissue. In percutaneous radiation, the prostate is treated with high-energy Photons (up to 15 MeV) are irradiated, resulting in a total energy dose of around 65 gray leads in the prostate region. Different forms of Brachytherapy is also used for treatment. In the HDR (high dose rate) brachytherapy becomes temporary hollow needles under local or full anesthesia into the prostate gland used. A computer-controlled one is then inserted into these hollow needles radioactive source introduced that there strictly localizes its dose to the prostate tissue. HDR brachytherapy of the prostate is combined in many cases used with percutaneous radiation therapy.

You are with all forms of therapy strives to achieve maximum tumor control, i.e. in the optimal Case the full destruction or removal of the tumor tissue. At the same time, it is imperative preserve healthy tissue to avoid side effects such as incontinence and Erectile dysfunction too minimize. A worldwide very gentle form of brachytherapy is the implantation of small radioactive nuclides in the prostate [1, 2]. It will be done with the help of transrectal ultrasound imaging elongated Iodine-125 (125-I) or Palladium-103 (103-Pd) sources, so-called seeds, implanted in the patient's prostate. The radioactive sources remain in the patient and sound there with a half-life from 59.5 days (125-I). The geometric dimensions of the seeds are 4.5 mm ± 0.2 mm in length and 0.8 mm ± 0.04 mm in diameter for all common manufacturers worldwide. The typical activity a single seed is 0.5 mCi on the day of surgery. at A preliminary patient examination will be performed with a transrectal ultrasound machine the prostate and the surrounding tissue are recorded sonographically and the image data is stored digitally. Based on these records radiation planning and the number of necessary Seeds set. Between 30 and 75 seeds are required per patient. Based An "online" radiation plan is created for the current ultrasound images Localization of the seeds in the prostate for each radiator individually sets. Such a dose and position calculation is used on commercial Programs for Treatment planning systems, for example VariSeed 6.7 from the company Varian, performed.

For The radiation planning is based on the following criteria: There is one in the prostate gland Aim for a homogeneous dose distribution of typically 145 Gy. This leaves achieve themselves through an equal distribution of the seeds. In addition, the Risk organs ureter (urethra) and rectum are spared to Avoid complications and side effects. The urethra begins in the bladder and runs directly through the prostate. A puncture of the urethra or a piercing the bladder must be avoided during the operation. Because the rectal mucosa is sensitive to radiation, is a corresponding distance between the emitters also to be taken into account by this body when planning.

So that the seeds to the intended Can be applied to the prostate, is first a Open needle at the tip guided to the appropriate position. to For better localization of the needle, use a template in the regular vertical and horizontal distances (typically 5 mm) pilot holes drilled are. This template is with the operating table and the ultrasound system connected so that a reproducible needle guide with the reference coordinate system given is. With the help of special application devices then the seeds into the prostate through the hollow needles pushed, the current penetration depth of the hollow needle of the implantation depth of the seed. In this way, all planned ones are successively Seeds implanted in the patient under anesthesia, with the entire Operation is accompanied by ultrasound imaging. This enables the Surgeon through the ultrasound echoes of the seeds a first visual Assessment of seed distribution in the patient's prostate. postoperative have to now the exact positions of the seeds are determined because of the localization with ultrasound machines is not exact enough. Especially when seeds are close together lying or in the sound shadow of an object (seed or limescale storage) the visibility of the radiation sources is severely impaired. In addition, air in the intestine often hinders the unrestricted view of the ultrasound sensor on the prostate region. For the subsequent follow-up planning become computer tomographs (CT) and sometimes also magnetic resonance tomographs (MRI) used.

A widely used and precise method of seed localization is the reconstruction of the seed positions from three X-ray images with different angular positions of the X-ray tube [3]. The patient is examined in the supine position, for example with the angles 45 °, 0 ° and -45 °, and corresponding X-ray images are taken. The recordings are usually not made with a diagnostic X-ray machine, but with a Simulation X-ray device specially developed for radiation therapy. The latter has a line laser system for easier positioning of patients and the same geometric setting options as a radiation device common in radiation therapy. Since X-ray-tight markings in the form of small wires or punctiform markers are built into the seeds, the identification of the seeds on the X-ray images or in CT is generally possible. The previously described position control by reconstruction from several X-ray images is easy to implement in the clinic, it is exact and is the only method that offers the possibility of reliably determining the orientation of the elongated emitters and thus taking them into account in the dose calculation. The transfer of the seed projections on the X-ray images into the planning program takes place using a digitizing table. The films are attached to this light table and with the help of a digital magnifying glass or a digitizing pen the origin of the coordinates, the orientation of the film and finally the individual seeds are digitized and serve as data records for the reconstruction algorithm. This calculates the position of the seeds in the patient and one compares this seed distribution with the one originally planned. This process is particularly important because inaccuracies in the application of the seeds can be detected here. Accurate follow-up planning is an indispensable means of quality assurance in order to guarantee the patients the same optimal quality of the seed implantation. On the one hand, the success of the treatment is optimized and, on the other hand, the probability of side effects is reduced to a minimum. For post-planning using a computer tomograph, the patient is scanned with the implanted seeds with a small CT layer thickness in the CT. Problems arise here from the formation of artifacts in the image data, which are caused by the metallic properties of the seeds. In particular, seeds lying close together can often not be clearly identified.

The known state of the art for the development of reconstruction methods that are capable of three-dimensional Seed positions from several X-ray films to determine is not yet complete, like current publications show [4]. It is not possible the accuracy of such an algorithm with high precision verify as there are no commercial phantoms for this purpose on the market. There are currently no options Reconstruction algorithms based on their accuracy and reliability to test: just as it is not possible to use subsequent planning CT precise to check. A such verification of calculation methods or reconstructions is of considerable importance in medicine because the user usually has to rely on the algorithm. Should actually be faulty Calculations take place, this can have a direct impact on the Radiation and thus the health of patients.

The object of the invention is a To create phantom model that for non-contact measurement evaluations Measurement data for exact localization of the seed positions and defined seed coordinates allows.

The invention is set out below Hand explained from nine drawings. The figures show in detail:

1 Overview of seed phantom,

2 Plexiglass end plate,

3 Plexiglass matrix disc,

4 Plexiglass pane with 2 holes asymmetrical,

5 Perspex pane with 2D angled holes 10 °,

6 Perspex with 2D angled holes 20 °,

7 Plexiglass pane with closely adjacent holes,

8th Plexiglass double pane,

9 Plexiglas solid material pane.

The phantom is on a carrier plate 101 about 200 × 150 mm in size with a thickness of 15 mm. This plate is on three adjusting screws 102 stored, the exact horizontal alignment using a small built-in spirit level 103 can be controlled. There is a square housing on the carrier plate 105 with plastic screws 104 appropriate. The central and most important parts of the phantom are plexiglass panes 106 , in the prefabricated holes of which non-radioactive seeds can be introduced. All discs have the same diameter and two side millings at the lower end 107 , The panes are initially loosened with the two millings on the precisely fitting upper edge of the housing 108 plugged. Then a safety bracket 109 in an upper groove 201 of the discs in order to achieve an even horizontal alignment. This securing bracket is rotatably mounted 110 at one end of the housing, can be stretched over the inserted plexiglass panes and at the other end of the housing by a plastic screw 111 secured in the closed position. The built-in panes are fixed horizontally in this way. In order to achieve an even pressure between the panes and thus exactly reproducible vertical pane positions, the Plexiglas panes lined up next to each other are screwed together 112 pressed together. A plexiglass buffer serves as a counter bearing 113 on the opposite side of the housing.

In radiation therapy, it is customary to position patients precisely on the radiation device, an X-ray device or the CT with the aid of several stationary line laser systems. With such a laser system, the phantom can also be opened exactly position on the patient table of the respective X-ray machine or CT. To make this easy, marking lines are engraved on the phantom surface, which can be brought into coincidence with the external positioning laser. This ensures reproducible storage of the seed phantom. Various types of round plexiglass panes are provided for the placement of the non-active seeds, which can be combined as desired. The round shape of the slices is intended to ensure uniform absorption of X-rays from all directions, which improves the image quality. The disks placed side by side become end disks on both sides 202 framed. They serve as an internal coordinate system and for determining the orientation of the phantom on an X-ray film or the CT data record. For this purpose, a metal ball is centered in one side of the end plate 203 glued in with the defined diameter of 2 mm. This is shown in high contrast on X-ray images and in the CT data set.

To secure the seeds, plexiglass disks are manufactured in such a way that the length of the seeds (4.5 mm ± 0.2 mm) can be inserted precisely into the disks. The discs have to be manufactured precisely because the seeds on the one hand do not protrude at the ends, and on the other hand they must not have too much play in their longitudinal direction. In the matrix disks 301 is a hole matrix 302 drilled with 5 mm vertical and horizontal hole spacing. A central hole 303 is located exactly in the middle of the plexiglass pane. For all dimensions of the holes for the seeds, the dimensions of the seeds with manufacturing tolerances must be observed. The seeds should be easy to insert and remove in any matrix holes with little play.

In addition to the matrix disks described, there are other disks with only a few drill holes 401 intended. Such disks are important to investigate the effects of air pockets in adjacent holes in the matrix disks. Different combinations and hole positions are possible. Matrix disks with angled drill holes 501 . 601 are also provided. With these discs every second hole 502 rotated in a defined direction (upwards, downwards, to the right or to the left) by a defined angle, for example 10 ° or 20 °, that is to say the drilling takes place obliquely in the plexiglass pane. It should be noted that the coordinate of the puncture point from the drilling channel corresponds to the coordinate of a matrix disk, since the positions of the seeds in the phantom with respect to the origin, i.e. the internal coordinate system, must be known exactly.

Another type of pane is a plexiglass pane with closely adjacent holes. Such a configuration is important in order to be able to differentiate seeds that are close together in the human body. A seed configuration in which the seeds vary in their longitudinal direction can be achieved with a special pair of discs. In two plexiglass panes 801 . 802 there are holes opposite 803 drilled, the total length of which corresponds to the length of a seed. The depth in the individual discs can differ from pair of holes to pair of holes. For example 0.7 mm and 4.0 mm, 1.7 mm and 3.0 mm, 2.7 mm and 2.0 mm or 3.7 mm and 1.0 mm. The sum of the two opposing hole depths remains constant (4.7 mm) and corresponds to the seed length including the manufacturing tolerance. This results in a variation of longitudinal seed positions in an associated plexiglass double pane. Here, too, the dummy seeds can be easily removed after a measurement by separating the two disks and pulling out the seeds at the protruding ends with the aid of tweezers. Between the plexiglass panes equipped with dummy seeds, panes with the same dimensions but without holes are placed 901 , This has the advantage that the seeds are fixed in the holes at the ends by the solid material disks and a shift in the longitudinal direction is prevented.

After inserting the seeds in any holes and the variable arrangement of the plexiglass panes, as previously described, placed on the casing of the phantom, with the safety bracket brought into the same orientation and fixed with the pressure screw.

The measurement process with the phantom is easy. For this purpose, it is placed on the patient table of the CT or X-ray machine and aligned using the three adjustment screws and the spirit level. Laser positioning systems allow a further reproducible position in relation to the respective device (CT or X-ray simulator). When used with a computer tomograph, a scan of the phantom is preferably carried out on the CT with a small layer thickness. The resulting image data set can either be carried out directly on the console of the CT or on the seed radiation planning program. Since the seeds have metallic markings, they can be recognized very well in the display and a position determination of the seeds on the digital data record, apart from faults due to artifacts, is generally easy to carry out. The determined positions of the individual dummy seeds are then compared with the positions in the phantom and the deviations are determined. If the parts of the phantom are manufactured with high precision (<0.1 mm), this reduces the multiplicative measurement errors of the overall system. In addition, since the dimensions of the plexiglass panes (thickness) and the coordinates of the holes in the phantom are known exactly, the position of the introduced seeds in the phantom can be determined very precisely in relation to the internal phantom coordinate system. Here, depending on the type requirement to set the midpoints of the seeds or their two endpoints. The latter is particularly important if the seed angle is to be determined using the oblique drill holes.

When checking a reconstruction algorithm from x-rays the phantom becomes similar as with the measurement on a computer tomograph on the patient table stored. With the X-ray machine or the Therapy simulator can now x-rays of the phantom from different directions. typically, three films with different positions of the X-ray tube (gantry rotation) needed. Since the recording parameters like the angle of the gantry rotation, the Distance of the phantom to the focus (focus-object distance) and the distance of the film on the focus of the X-ray tube for the subsequent reconstruction calculations important, these must be for every Measurement on the device be read. With the help of a digitizing table on the Treatment planning computer is connected, the seeds digitized individually and their positions on the film transferred to the treatment planning program. The reconstruction algorithm calculates from the films of a series of the seed treatment planning program the three-dimensional coordinates of the dummy seeds in the phantom. This Data is now displayed with the known positions of the seeds in the phantom compared and deviations quantified.

The parts of the phantom - disks like mounts - should so precise that the recommended in the international literature Accuracy in the reconstruction of less than 2 mm [5] maintained can be.

source reference

• 1. T. W. Kaulich, U. Lamprecht, F. Paulsen, F. Kahmann, U. Maurer, T. 0. Henkel, W. Loeser, F. Nüsslin, M. Bamberg: Physical basics and clinical implementation of the interstitial prostate brachytherapy with iodine-125. Strahlenther. Oncol. 178 (10) 2002 548-555
• 2. D. Ash, A. Flynn, J. Battermann, T. de Reijke, P. Lavagnini and L. Blank: ESTRO / EAU / EORTC recommendations on permanent seed implantation for localized prostate cancer. Radiother. And Oncol. 57 (3) 2000 315-321
• 3. H. I. Amols, I. I. Rosen: A three-film technique for reconstruction of radioactive seed implants. Med. Phys. 8 (2) 1981 210-214
• 4. I. B. Tutar, R. Managuli, V. Shamdasani: Tomosynthesis-based localization of radioactive seeds in prostate brachytherapy. Med. Phys. 30 (12) 2003 3135-3142
• 5. D. Tubic, A. Zaccarin, L. Beaulieu, J. Pouliot: Automated seed detection and three dimensional reconstruction. II. Reconstruction of permanent prostate implants using simulated annealing. Med. Phys. 28 (11) 2001 2272-2279

Claims (9)

Plexiglass seed phantom for X-ray diagnostics for 3-D image processing processes in which the measurement object is irradiated, characterized by a carrier plate ( 101 ) on three adjusting screws ( 102 ) is mounted on which a housing ( 105 ) with plastic screws ( 104 ) is attached into the plastic discs ( 106 ) can be clamped with the same diameters and thicknesses with an upper groove ( 201 ) are provided for the purpose of fastening the plastic washers ( 106 ), with a safety bar ( 109 ), holes in the plastic washers ( 302 . 502 . 803 ) are introduced, into which radiopaque seeds can be inserted as measurement objects. Plexiglass seed phantom according to claim 1, characterized by plastic discs ( 106 ) with more or less holes ( 502 . 803 ), into which seeds with standardized dimensions and deviations can be inserted and removed. Plexiglass seed phantom according to claim 1 and 2, characterized by plastic discs ( 106 ) which are shaped in such a way that uniform absorption of X-rays is guaranteed from all sides. Plexiglass seed phantom according to claims 1 to 3, characterized by two end plates ( 202 ), each with a metal ball in the middle ( 203 ) with a defined diameter as internal reference coordinates. Plexiglass sea phantom according to claims 1 to 4, characterized by plastic panes ( 106 ), which are made of material with a uniform absorption coefficient for X-rays. Plexiglass seed phantom according to claim 1 to 5, characterized by a matrix disc ( 301 . 501 . 601 ) into which a hole matrix ( 302 ) with a small vertical and horizontal hole spacing. Plexiglass seed phantom according to claim 1 to 6, characterized by a matrix disk ( 301 ) as a shadow mask ( 501 . 601 ), into the angled drill holes ( 502 ) are introduced, with every second hole in a defined direction through a fixed, alternating angle with oblique holes in the plastic disc ( 106 ) is introduced. Plexiglass seed phantom according to claim 1 to 5, characterized by two plastic discs ( 801 . 802 ), in the opposite holes ( 803 ) are introduced, the total length of the length corresponds to two seeds. Plexiglass seed phantom according to claim 1, characterized through coincidence marking lines for line laser alignment systems.