WO2000039608A1 - Fixing device for dosimeter, device and method for monitoring dynamically produced spatial dose distribution - Google Patents

Abstract

The inventive device for monitoring dynamically produced spatial dose distributions is provided with at least two dosimeters which are arranged on a fixing device in a defined spatial relation to one another. Said dosimeter, when mounted on an arm of a motor-driven water phantom, can be automatically positioned, their positions can be measured and saved and desired dose values can be calculated for each dosimeter. In this manner, the spatial dose distribution can be monitored comparatively quickly or on-line by comparing the desired dose values with the measured dose values.

Description

 Dosimeter holder, device and method for checking dynamically generated spatial dose distributions

The invention relates to a dosimeter holder, a device and a method for practicing dynamically generated spatial dose distributions.

With dynamic radiation techniques, especially in the

Radiation therapy, by changing over time

Irradiation parameters, for example by changing the beam diaphragms of a multileaf collimator, generated complex three-dimensional dose distributions. Since the change in the radiation parameters is carried out simultaneously with the radiation, the correct sequence of this process must be ensured for the safety of the patients.

For this purpose, the radiation plan actually to be carried out on the patient is carried out before the radiation and the dose distribution generated in this way is measured at representatively selected points in the water phantom. The measured dose values are then compared with the dose values specified by the radiation planning for the corresponding phantom structure. In this respect, the entire radiation plan must be carried out in order to determine the dose at a point in space.

To save time, several ionization detectors are positioned in a water phantom or similar at the same time. These ionization detectors can be connected to multichannel electrometers so that all dose values can be determined simultaneously.

As an alternative to these ionization detectors, others can also be used

Detectors, e.g. Semiconductor detectors to be positioned in a phantom.

In all of these arrangements, a complex individual evaluation of the ionization detectors or dosimeters must then take place.

In particular, the exact spatial points of the dosimeters or ionization detectors must be determined. In addition, it is extremely time-consuming to position the dosimeters or the ionization detectors in the desired manner.

It is an object of the present invention, a significantly more time-saving and reliable check of dynamically generated spatial

Allow dose distributions.

As a solution, the invention proposes on the one hand a dosimeter holder which comprises a holder on which at least two Dosimeters are arranged in a defined spatial relationship to one another, the holder having at least one preferred blasting device and the dosimeters being arranged on the holder in steps and offset in the beam direction.

With such an arrangement, on the one hand, it is only necessary to determine the spatial position of one of the dosimeters. Due to the defined spatial relationship to the second dosimeter, the position of the second dosimeter is subsequently known.

With such an arrangement, the position determination can thus be carried out much faster since only one position has to be determined. This also reduces the risk of a measurement error.

The more dosimeters are arranged on the holder in a defined spatial relationship to one another, the greater the time or the risk of error is reduced.

Since the dosimeters are arranged in stages on the holder, there is a free direction for the dosimeters arranged in each case from which a beam can freely reach each of the dosimeters. In addition, this arrangement makes it possible to measure different depths in a water phantom or the like with a holder. The offset enables an unobstructed beam path to each individual dosimeter. It is advantageous here if the dosimeters or detectors are packed as densely as possible. In particular, the "dense packings" known from the geometry can be used here. In particular, it is advantageous if the dosimeters or detectors do not overlap or partition off one another in the preferred beam direction.

In the present context, the term dosimeter encompasses any device that is able to determine a radiation dose at a specific point in space or in a specific volume. It includes ionization detectors in particular, but also other detectors, e.g. Semiconductor detectors. In particular, individual assemblies of the dosimeters can also be arranged at a different location, as is the case, for example, with

Electrometers is the case, which are connected to ionization detectors. Dosimeters and detectors that can be read online are particularly suitable for this, so that dose verification can be carried out correspondingly quickly.

Checking the dose distribution is particularly easy if the holder rigidly connects the dosimeters. With such an arrangement, the spatial relationship of the dosimeters to one another is fixed and can be included in the check as a constant variable. Because there are usually certain standard types of radiation plans that are in some way Standardizable arrangements of dosimeters can be checked, a limited number of such holders, which rigidly connect the dosimeters, is sufficient to carry out most of the tasks for checking dose distributions.

It may be sufficient to provide a holder for a longitudinal section, a holder for a cross section, a holder for cross profiles and a holder for depth profiles. These differ from each other in the specific arrangement of the dosimeters.

On the other hand, it is also conceivable that the holder is designed such that the spatial relationship of the dosimeters to one another can be changed in a defined manner. A wide variety of adjustment devices can be used for this purpose, as long as a resulting adjustment takes place in a traceable or measurable manner.

The prescribed arrangements also make it possible, in particular, that the individual dosimeters do not have to be positioned at different heights in a complicated and error-prone manner.

The holder can also be a means for measuring a

Include dosimeter position. On the one hand, the position of each individual dosimeter can be detected by these measuring devices.

On the other hand, it is also possible that only the position of the Bracket is measured and the individual dosimeter positions are determined on the basis of this measurement and the defined spatial relationship of the dosimeters to one another or to a reference of the bracket. Since these measuring devices carry out a purely mechanical measurement, this reduces the possibility of error, which occurs at

Prior art arrangements in which each individual position of each dosimeter had to be determined separately manually were considerable.

In addition, means for storing the dosimeter position can be provided. The dosimeter positions can easily be made available for further processing from such a memory. In particular, it is also possible to connect the storage means to the measuring means in such a way that the measured dosimeter positions are stored directly in the storage means.

The check can also be accelerated if the holder is connected to a positioning device. In particular, this can be a positioning device of a water phantom. At this point, however, positioning devices of other devices that are used to check a dose distribution can also be used.

Here, the check is particularly simple if the positioning device has means to determine the position of the Positioning device to determine. Since the holder is connected to the positioning device, the position of the holder and the dosimeter is also known or measurable in this way.

It is understood that the term in the present context

"Position" also includes a direction. Depending on the design of the checking device, however, the direction of the holder can be fixed and therefore known.

As a solution, the invention further proposes a device for

Review of dynamically generated spatial dose distributions, which include a holder for at least one dosimeter, means for measuring the dosimeter position, means for calculating target dose values for each dosimeter corresponding to the dosimeter position and means for comparing the measured dose values with the calculated ones

Target dose values included.

The means for calculating target dose values at the dosimeter position can in particular comprise a memory in which an irradiation plan (dose cube) can be stored. Here, the calculation means are advantageously able to output target dose values for certain positions, so that such target dose values can also be output for the current dosimeter positions. This can be done, for example, by means of suitable interpolations if the radiation plan in

There is a form of position-dependent dose values. on the other hand O

The calculation means can also include other simulation tools that are able to calculate location-dependent target dose values from a given radiation plan. Averaging over the measuring volume can be carried out for the type of dosimeter used.

The comparison by the means for comparing the target dose values with the dose values measured by the dosimeters can be done, for example, by specifying corresponding relative numbers, percentage deviations or other statistical statements. For this purpose, the individual detectors can also be deactivated or activated in a simple manner. The statistical parameters for the deviations are recalculated instantaneously for the active detectors. This can also be done by means of a graphic or pictorial representation. The comparison means can be directly connected to the measuring means and the calculation means, so that the comparison can take place without further manual intervention. In this way, the checking speed can be increased further. The fact that no manual data exchange or manual data entry is required also increases the reliability of the checking device.

The checking device preferably has means for storing the dosimeter position so that it is directly used for the necessary calculations and checks

Available. In addition, means can be provided for calculating the target dose values on the basis of the dosimeter position and a predetermined dose cube or radiation plan, in particular on the basis of these stored data but also after the data has been entered in some other way.

In addition, the checking device can have means for documenting the checking. In particular, these can include a corresponding expression. On the other hand, documentation on another storage medium, such as a floppy disk or the like, is also possible. Such documentation is advantageous for medical law reasons and also guarantees the treating doctor a permanent and reliable overview of the radiation that has occurred.

As a further solution, the invention proposes a method for checking dynamically generated spatial dose distributions, in which at least one dosimeter is positioned via a holder, the position of which is measured and stored, and for which dosimeters are calculated and compared with the currently measured dose values. This method according to the invention ensures, particularly in interaction with the device according to the invention, a reliable determination of target dose values at dosimeter positions, so that a dose distribution can be checked relatively quickly and reliably. The target dose values can preferably be calculated on the basis of the dosimeter positions and a radiation plan or dose cube.

Before the actual positioning of the dosimeters by means of the positioning device connected to the holder, the positioning device can be brought into a reference position and a location calibration can be carried out. If the positioning device is subsequently moved, the relative can

Change in position, the position of the bracket and thus the position of the dosimeter can be determined. With such a procedure, even if there is an interim change in the positioning device between different checking methods or different treatments, it is sufficiently precise

Determination of the dosimeter positions guaranteed.

It goes without saying that the above-described measuring means, storage means, calculation means, comparison means and the means for documenting the check as well as the holder according to the invention or its

Connection to the positioning device, both individually and cumulatively, increases the reliability and speed of a check of dynamically generated spatial dose distributions. The invention is therefore based on the inventive basic idea of steps carried out up to now as time-consuming and faulty individual activities, such as positioning the dosimeter Recording of measured values and their processing as well as the documentation, to be brought together in a suitable manner.

The invention thus provides a completely new generation of checking devices, which only make everyday use of dynamic radiation techniques possible. Only the invention enables a reliable, less time-consuming and therefore inexpensive check of the dose distributions generated with these radiation techniques.

In particular, a suitable configuration of the invention or its embedding in an overall arrangement or overall method can be used to check the dose distribution online. Here, the actual check can be a simulation that is verified online or almost online at singular points, ie the detectors, or in certain spatial areas, with detectors extending spatially over a certain area. It is at the discretion of the respective user which degree of verification of the simulation is required until it is recognized as sufficiently precise and thus used for a check.

Further advantages, goals and properties of the present invention are explained with reference to the following description of the attached drawing, in which an example of a checking method according to the invention and components of a checking device according to the invention are shown. The drawing shows: FIG. 1 shows a process sequence for checking dynamically generated spatial dose distributions,

FIG. 2 shows a screen surface of a computer executing the method according to FIG. 1,

FIG. 3 shows another screen surface of the computer executing the method according to FIG. 1,

FIG. 4 shows a first holder for ionization detectors in supervision,

FIG. 5 shows the holder according to FIG. 4 in section,

FIG. 6 shows a second holder for ionization detectors in supervision,

FIG. 7 shows the holder according to FIG. 6 in section,

Figure 8 is a third bracket for ionization detectors in supervision and

Figure 9 shows the bracket of Figure 8 in section.

The system shown as an example for the examination of dynamically generated spatial dose distributions comprises two 12-channel

Electrometer (Multidos I and Multidos II; from PTW, Freiburg), the with 24 ionization detectors (type IC03; Wellhöfer, Schwarzenbruck; numbered in FIGS. 4, 6 and 8 by way of example). In addition, this system includes a known, motor-driven three-dimensional water phantom (MP3; PTW, Freiburg) with a corresponding control device.

The system further comprises at least one holder for the ionization detectors, which is connected to a positioning arm of the motor-driven three-dimensional water phantom. As explained in more detail below, various brackets can also be provided for the ionization detectors, so that the variability or the area of application of this system is increased. In addition, the system includes a data processing device, which is connected to the 12-channel electrometers and the water phantom via suitable interfaces.

Before the actual check of the dynamically generated spatial dose distribution begins, the desired distribution or the radiation plan (dose cube) is loaded into the data processing device. An ionization detector holder suitable for the type of radiation is also attached to the arm of the water phantom. The water phantom is aligned relative to the radiation system in such a way that a useful beam is incident through an inlet of the water phantom and the center of the input surface lies in the isocenter of the radiation system. The movable arm of the water phantom is brought into a reference position with a hand switch. Then the corresponding measured values are shown by Means for measuring the position of the Wasseφhantomarmes are recorded, stored as reference values. A location calibration is carried out in this way. This location calibration is preferably carried out via a corresponding control menu. Using this control menu, the arm of the water phantom and thus the ionization detector holder can now be moved to a desired position. By means of the position measurement, the exact position of the water arm and thus also the exact position of the holder with its ionization detectors can be measured. The respective position is shown on a screen of the

Represented data processing device, so that a desired positioning can be carried out easily, sitting at a terminal of the data processing device (see lower area of Figure 3). As can be seen in this lower area, the position of the ionization detectors is shown relative to the desired dose distribution (dose cube), so that the position can be checked visually exactly without further measures.

At the measuring position determined in this way, the setpoint values are then set by the data processing device for all ionization detectors.

Dose values are calculated after the position of the dosimeter has been stored appropriately.

From the terminal, after the holder or the ionization detectors are positioned in the desired position, the radiation plan is run through and the measurement is initiated started. The doses falling into the ionization detectors (IC03) and measured by the 12-channel electrometers (Multidos I and Multidos II) are saved and compared with the target dose values. This is done in that the data processing device calculates the graphical representation of the difference between the measured value and the desired value and the mean value and the standard deviation and outputs them as numerical values (see FIG. 2).

In this way it can be quickly and reliably decided whether the dose distribution generated meets the medical requirements.

The data processing device is also provided with a printer by means of which the corresponding data can be printed out. On the one hand, this can be a tabular representation of the test parameters and the test result.

Corresponding graphics can also be printed out.

Such a printout is particularly easy to provide by means of a 1: 1 printout of the screen representations of the data processing device.

The arrangement described is in particular able to carry out a simulation of the dose distribution on the dose cube online or almost online, using the simulation and the

Detektoφositionen to calculate the target dose values and these with to compare the dose values actually measured at these positions and thus to check them.

The bracket used in the arrangement described above - three different exemplary embodiments are shown in FIGS. 4 to 9 - each have 24 bores 33 (numbered as examples) in a plexiglass body 31, which are arranged parallel to one another.

On a side of the plexiglass body 31 perpendicular to the bores, a cover 32 with bores 34 (numbered as an example) is provided, which are smaller than the bores 33 but are arranged identically to them.

In this way, 31 recesses are created in the plexiglass body, in which the ionization detectors 1 to 24 can be arranged. The Plexiglasköφers 31 also has an attachment, not shown, with which this can be attached to a Wasseφhantomarm.

The holder shown in FIGS. 4 and 5 serves to measure a level of a dose distribution either in longitudinal section or in cross section. The two-dimensional arrangement of the detectors is as narrow as possible. In order to be able to record a profile, the plexiglass body 31 has on the side of the cover 32

Levels 35. For measuring a longitudinal section or Longitudinal profile of the Plexiglasköφers 31 is arranged such that a beam is incident parallel to the direction of the arrow A in Figures 4 and 5. To check a plane in cross section, the plexiglass body 31 is arranged such that a beam is incident along the direction of the arrow B in FIG. 5.

The embodiment shown in FIGS. 6 and 7 also has steps and is arranged along the incident beam to record a depth dose profile.

The holder shown in FIGS. 8 and 9, on the other hand, has a flat cover 32 and is used to hold profiles. For this purpose, the holder is arranged transversely to the incident beam.

It goes without saying that, depending on the number of ionization detectors and on the required measurement profile, other mounting forms can also be used, as long as they create a defined spatial relationship between the ionization detectors. By using multiple detectors, these arrangements allow a particularly economical check of the dose distributions.

Claims

Claims: 1. Dosimeter holder, on which at least two dosimeters are arranged in a defined spatial relationship to one another, the holder having at least one preferred blasting device, characterized in that the dosimeters are arranged on the holder in steps and offset in the beam direction. 2. Holder according to claim 1, characterized in that the holder rigidly connects the dosimeter. 3. Holder according to claim 1 or 2, characterized in that the holder is connected to a positioning device, preferably a Wasseφhantoms. 4. Holder according to one of claims 1 to 3, characterized by means for storing the position of the dosimeter. 5. Holder according to claim 4, characterized by means for calculating target dose values at the position of the dosimeter. 6. Holder according to claim 5, characterized by means for comparing the target dose values with the dose values measured by the dosimeters. 7. The device for checking dynamically generated spatial dose distributions, in particular with a holder according to one of claims 1 to 6, characterized by a holder for at least one dosimeter, means for measuring the dosimeter position, means for calculating target dose values for each dosimeter in accordance with the dosimeter position and means for comparing the measured dose values with the calculated target dose values. 8. The device according to claim 7, characterized by means for storing the dosimeter position. 9. The device according to claim 7 or 8, characterized by means for calculating the target dose values based on the dosimeter position and a predetermined dose cube or radiation plan. 10. The device according to one of claims 1 to 9, characterized by means for documenting the test. 11. A method for checking dynamically generated spatial dose distributions, characterized in that at least one dosimeter is positioned via a holder, the position of which is measured and stored and target dose values are calculated for the dosimeter and compared with the currently measured dose values. 12. The method according to claim 11, characterized in that the target dose values are calculated using the Dosimeteφositionen and a radiation plan or dose cubes. 13. The method according to claim 11 or 12, characterized in that before the positioning of the dosimeter, a positioning device which is connected to the holder is brought into a reference position and a location calibration is carried out.