Patent Application
20150190655
The invention relates to a method of determining a radiation distribution, a data processing for implementing the method, and to a radiation planning system.
Radiation treatment of patients is usually preceded by a radiation planning stage. Radiation planning involves the determination of radiation doses to which the patient is to be exposed during treatment. This may include a spatial distribution of the radiation dose and/or a distribution of the radiation dose over time. The spatial distribution and the distribution over time will generally be referred to as radiation distribution herein.
For the purpose of quality control, the radiation distribution determined in the radiation planning stage is compared with measurements of the actual radiation distribution during simulated treatment using a so-called phantom, i.e. a more or less body-equivalent device replacing a patient during a simulated radiotherapy and enabling measurements within the volume to be irradiated. Differences between the measurements and the predetermined radiation distribution can be taken into account when correcting the radiation treatment plan.
It is an object of the present invention to improve the radiation planning so that the differences between the predetermined radiation distribution and the actual (measured) radiation distribution are reduced to a minimum.
According to one aspect of the present invention, there is provided a method of determining a radiation distribution, comprising: determining or estimating movements of a patient during a radiation exposure; exposing a phantom to radiation, wherein the radiation exposure of the phantom corresponds to an intended radiation exposure of the patient; measuring first radiation values at respective first positions during the radiation exposure of the phantom; and calculating second radiation values at respective second positions based on said first radiation values and values of one or more parameters indicative of said movements of the patient.
The present invention is based on the realization that radiation planning can be improved by taking into account the movements of a patient during treatment. In particular, the present invention is directed to taking into account patient movements already in the radiation planning stage. Such movements may be movements of the entire or part of the patient, e.g. movements caused by breathing.
Patient movements are taken into account by simulating the movements of regions of interest of the phantom. For this purpose, the algorithm that is used to calculate the second radiation values from the first radiation values takes into account the movement of such regions of interest. Such algorithm can—in the easiest case—simply consist of the convolution of the four-dimensional set of dose measurement values with a corresponding four-dimensional set of motion vectors.
The first and second positions may be identical. This enables determining how a radiation dose at a given position changes from an initial value (the first radiation value) to a subsequent value (the second radiation value) due to patient movements.
Alternatively, the second positions may be different from the first positions. The second radiation values indicate whether a position of interest is exposed to sufficient radiation and/or whether surrounding tissue and vital organs at risk are subjected to an inacceptable dose level.
Also, the first and second positions may represent regions. The regions represented by the first and second positions may be identical, or they may entirely or partly overlap. In this embodiment, regions of interests, for example regions containing tissue to be destroyed, can be examined.
The first and second radiation values may represent radiation intensities or doses. and may be included in a three-dimensional matrix. From such matrix, it is possible to extract and examine the radiation in selected planes and/or from selected angles.
In addition, it is possible to determine the distribution of the first and second radiation values over time. This enables the examination of selected periods or phases of the treatment.
In an embodiment of the invention, the first radiation values are measured through sensors placed at or in the phantom or a treatment couch on which the phantom is supported, wherein, during the radiation exposure of the phantom, radiation from a radiation source passes through at least a portion of the phantom before reaching or impinging on said sensors.
In an embodiment of the invention, the method comprises generating a depth dose or tissue phantom rate curve associated with the patient or a phantom representing the patient; adapting the depth dose or tissue phantom rate curve in accordance with the movements of a patient during a radiation exposure; and determining the second radiation values on the basis of the first radiation values and the adapted depth dose or tissue phantom rate curve. A depth dose or tissue phantom rate curve indicates the distribution of the radiation dose along the trajectory of the radiation. Accordingly, it is possible to obtain a relatively high number of radiation values distributed in three-dimensional space on the basis of a relatively low number of measurement values in a single plane. In particular, it is possible to derive values at positions along the trajectory above or underneath the plane in which the sensors are located. For example, the values in three-dimensional space can be obtained by multiplying the measurement values with associated values of the depth dose or tissue phantom rate curve.
Generally, patient movements may be measured, estimated or determined empirically. The movements may be represented by a mathematical function, e.g. a sinus or elliptical function indicative of periodical movements such as movements caused by breathing, wherein the amplitude is determined empirically. In another embodiment, the movements may be represented by values in a lookup table or matrix.
In an embodiment, the method comprises deriving the parameter values indicative of the patient movements from data obtained from a control device associated with an adjustable treatment couch, the control device to dynamically cause adjustments of the treatment couch in accordance with movements of a patient during treatment. By using data obtained from such control device it is possible to empirically determine patient movements without requiring additional equipment or measurements.
Alternatively, it is possible to derive the parameter values indicative of the patient movements from data obtained from a measurement device for measuring movements of the patient or parts of the patient during treatment, wherein the measurement device may comprise one or more acceleration sensors attached to the patient and/or an X-ray, magnetic resonance, laser and/or an ultrasound apparatus. This embodiment enables precisely determining patient movements in specific regions of interest.
According to another aspect of the present invention, there is provided a data processing system comprising: Means to obtain or store values of one or more parameters indicative of movements of a patient during a radiation exposure; means to obtain measurements of first radiation values at respective positions during a radiation exposure of a phantom; and means to determine second radiation values based on said first radiation values and said obtained or stored parameter values.
The data processing system may be included in a radiation therapy quality assurance (QA) system comprising an array of sensors located at different respective positions in or at a phantom and/or a treatment couch supporting the phantom, for measuring first radiation values during a radiation exposure of the phantom.
The radiation therapy QA system may further comprise one or more phantoms having at least some of said array of sensors located in or at the phantom. The phantom preferably has one or more predetermined characteristics that correspond to those of a patient who is to undergo radiation treatment. In particular, the phantom has essentially the same transmissibility or permeability characteristics for the type of radiation that is used for the radiation treatment of the patient.
Accordingly, the present invention may be advantageously implemented by or integrated with a quality control or management system consisting of or comprising a phantom for providing the first radiation values and software for calculating the second radiation values.
The present invention enables the recalculation of radiation doses over space and/or time during the planning stage of a radiation treatment, taking into account estimated movements of the patient during the treatment.
In an embodiment of the invention, a set of vectors indicative of the location of voxels of the patient is generated. This is done on the basis of a model, predetermined information and/or measurements. The vectors are 4-dimensional: three dimensions in space and one dimension in time. Initially, the value of all vectors is zero.
The set of vectors include information indicative of one or more of the following parameters:
Deformation of the patient
Possible movements of the patient
Possible movements of the treatment couch
Other relevant movements of deformations
Measurements of the stationary phantom indicate when and what the linear accelerator radiates, and in which direction. The measurements also provide 4-dimensional data: the dose is measured in one plane (2D), while the dose along the depth is reconstructed (1D); this is done over time (1D). At this stage neither the treatment couch nor the phantom needs to be moved, thus simplifying the measurements.
By means of such 4D dose distribution, the doses in the patient can be calculated, using the patient's CT. The CT used in this step does not include or reflect any patient movements or deformations. Such movements or deformations are taken into account in the next step. Using the 4D vectors, the patient CT is deformed. Using the 4D dose distribution, the dose distribution in respect of the deformed CT is calculated for each point in time. Thereby, the doses that the patient is exposed to due to his movements and deformations are obtained. From such dose distribution, the doses at the patient target volume (PTV) or at organs at risk (OAR) can be derived.
An embodiment of the invention will now be described by reference to the drawings. In the drawings,
In step 2, data indicative of the patient movements is stored. In particular, the data is stored in the memory of a data processing system that is provided to control and/or perform the steps of the described method.
In step 3, a phantom is placed on the treatment couch. The phantom should have the same or a similar basic anatomy as the patient to be treated. Also, the phantom should have essentially the same characteristics as the patient in terms of transmissibility or permeability for radiation.
In step 4, radiation sensors are placed in or at the phantom and/or the treatment couch so that radiation emitted by a radiation generator passes through portions of the phantom before reaching the sensors. In an embodiment, the sensors are integrated with the phantom.
In step 5, the phantom is exposed to radiation emitted by a radiation generator. The radiation doses, in particular the distribution of the radiation doses over time and/or space corresponds to the radiation doses intended for the radiation treatment of the patient.
In step 6, the radiation is measured by the sensors. The measurement values are stored in the memory of the data processing system.
In step 7, the measured patient movements and the measured radiation values are used to calculate second radiation values. In particular, the second radiation values are based on the measured radiation values and additionally reflect the movements of the patient.
In step 8, the second radiation values are used to adapt the radiation doses, in particular the distribution of the radiation doses over time and/or space, intended for the radiation treatment of the patient, thereby to eliminate effects caused by the patient movements.
The radiation generator 13, the apparatus 14 and the sensors 15 are connected to a data processing and control device 16. The data processing and control device 16 is arranged to cause some or all of the steps illustrated in
Subsequently, when the phantom 12 is placed on the treatment couch 11, the data processing and control device 16 controls the sensors 15 to measure the radiation, and receives and stores the measured radiation values.
The data processing and control device 16 uses the data indicative of the patient movements and the measured radiation values to calculate second radiation values by e.g. convoluting the measured radiation values with the corresponding displacement vectors previously determined.
This means that the four-dimensional set of dose data values, obtained e.g. by continuously measuring in one plane of a cylindrical phantom—which itself is always oriented perpendicular to the radiation beam's central axis by the control device—and continuously adding calculated (by depth dose curve or tissue phantom rate) values for the rest of the cylindrical phantom's volume, is displaced by an equally four-dimensional set of vectors determined from the patient movement data into a new four-dimensional set of dose data values distributed over the treatment time and the volume of the phantom. These can then be used for a more realistic appraisal of the treatment plan.
Accordingly, the second radiation values reflect expected movements by a patient. In other words, the second radiation values represent values that would have been measured if the phantom had moved or had been deformed in accordance with the measured patient movement.
The data processing and control device 16 compares the second radiation values with the measured radiation values. The difference between the measured radiation values and the second radiation values indicates the effect on the radiation at the sensors 15 caused by the patient movements. For example, if the second radiation value is higher than the measured radiation value, this indicates that more radiation than expected has passed through the corresponding portion of the phantom 12.
The data processing and control device 16 may be used to adapt a stored radiation distribution for use in a subsequent radiation treatment, for example to reduce the radiation directed to a given area if the second radiation values in that area indicate a higher-than-expected radiation.
| Number | Date | Country | Kind |
|---|---|---|---|
| 14 150 635.2 | Jan 2014 | EP | regional |
