Patent Description:
Cancer treatment, in particular lung cancer treatment, is constantly evolving due to technological advances in the delivery of radiation therapy. Adaptive radiation therapy (ART) allows for modification of a treatment plan with the goal of improving the dose distribution to a patient due to anatomic and/or physiologic deviations from the initial simulation. Cancer radiation treatment planning may be based on 4D CT data (four-dimensional computed tomography data). A 4D CT simulation may be applied onto the 4D CT data, generating a snapshot of the tumor size, shape, and position relative to normal tissue, which is used for the creation of an internal gross tumor volume (IGTV) or internal target volume (ITV). While the technologies to treat these tumors allow for highly conformal dose distributions, the complex geometric uncertainties involved in lung cancer treatment planning require large safety margins to create the planning target volume (PTV), which may hamper dose escalation.

Document <CIT> discloses a method for calculating a 3D patient representation during a particular radiation treatment fraction session based on intrabody imaging data, such as from 4D CT images, surface imaging data and surface camera imaging data.

Additionally, since treatment cycles and the overall duration of the treatment are typically quite long in radiation therapy it can happen that there are weeks between the acquisition of the planning images and the actual treatment. This constitutes the risk of poor tumor coverage and more severe off-target effects. ART addresses these weaknesses by enabling periodic changes to the treatment plan. 4D CT image acquisition however may pose a non-neglectable dose burden for the patient, for example, in the region of <NUM> to <NUM> mGy. Therefore, adaptive planning for moving tumors in liver and lung poses a challenge of additional dose burden. This restricts clinicians to follow the approach of a "plan of the day" wherein the initial treatment plan is adapted just before each treatment to improve accuracy.

The underlying technical problem of the invention is to facilitate an adaptive treatment planning in medical radiology that is improved in particular with regard to radiation dose and image quality. This problem is solved by the subject matter of the independent claims. The dependent claims are related to further aspects of the invention. Independent of the grammatical term usage, individuals with male, female or other gender identities are included within the term.

The invention relates to a computer-implemented method for providing adapted 4D CT data, the method comprising:.

In particular, the anatomical structure may be an antomical structure of a patient. The anatomical structure may be, for example, an organg, in particular a lung or a liver. The anatomical structure may comprise a lesion, for example a tumor.

4D CT data may relate to three dimensions of space and one dimension of time. The dimension of time may relate, in particular, to a breathing signal and/or a sequence of breathing phases. The first 4D CT scan may be a first full quality 4D CT scan. Compared to the first 4D CT scan, the partial 4D CT scan exposes the anatomical structure to less radiation dose, thereby compromising on image quality, image resolution, time resolution and/or scan range. In particular, the initial 4D CT data may cover at least one 4D sample point that is not covered by the supplementary 4D CT data.

An initial treatment plan may be calculated based on the initial 4D CT data. For example, a first representation of the anatomical structure may be calculated based on the initial 4D CT data, the first representation of the anatomical structure relating to the anatomical structure on the first examination date. In particular, first information relating to a size and/or motion of a tumor of the anatomical structure and/or to an anatomical and/or morphological situation in the patient may be calculated based on the initial 4D CT data. The initial treatment plan may be calculated, for example, based on the first representation and/oder based on the first information.

An adapted treatment plan may be calculated based on the adapted 4D CT data. For example, a second representation of the anatomical structure may be calculated based on the adapted 4D CT data, the second representation of the anatomical structure relating to the anatomical structure on the second examination date. In particular, second information relating to the size and/or motion of the tumor of the anatomical structure and/or to the anatomical and/or morphological situation in the patient may be calculated based on the adapted 4D CT data. The adapted treatment plan may be calculated, for example, based on the second representation and/oder based on the second information.

To lower the dose burden for an adaptive replanning, in particular for an update of the treatment plan right before the actual treatment (to create a "plan of the day") or at defined time points during the treatment, the initial 4D CT data may be used as prior information and modified based on up-to-date information from the supplementary 4D CT data. The usage of prior information from the initial 4D CT data may help to reduce the dose burden of adaptive updates of the 4D CT planning data set during radiation treatment planning, in particular in form of incremental replanning.

For example, the second 4D CT scan may be essentially equivalent to a repeat of the first 4D CT scan on the second examination date. In particular, the second examination date may be later in time than the first examination date. For example, the second examination date may occur at least two days after the first examination date, at least one week after the first examination date and/or at least one month after the first examination date.

The proposed method may enable a dose-reduced workflow for 4D CT imaging which would allow for an adaptive recalculation of treatment plans during different fractions of a treatment in order to adapt the radiation plan to changes during the treatment. The changes may relate, for example, to a tumor size, a tumor motion, a morphology and/or a situation of tissue surrounding the tumor.

Since there might be several weeks between the acquisition of the initial 4D CT data and the actual treatment such a method may help to signigicantly increase the quality, effectiveness and accuracy of radiation treatment planning while keeping the additional dose burden low.

A radiation dose may be reduced, in particular significantly reduced, for the partial 4D CT scan compared to the first 4D CT scan. In particular, the partial 4D CT may be dose-reduced with respect to the first 4D CT scan by an order of magnitude, for example to enable approaches like performing a 4D CT based adaptive replanning or even going into the direction of a "plan of the day". The radiation dose of the second 4D CT scan may be comparable, in particular essentially equivalent, in particular equivalent, to the radiation dose of the first 4D CT scan.

The radiation dose of the first 4D CT scan may be higher than <NUM> mGy, in particular higher that <NUM> mGy, and/or smaller than <NUM> mGy, in particular smaller that <NUM> mGy. The radiation dose of the partial 4D CT scan may be smaller than <NUM> % of the radiation dose of the first 4D CT scan, in particular smaller than <NUM> % of the radiation dose of the first 4D CT scan, in particular smaller than <NUM>% of the radiation dose of the first 4D CT scan. The radiation dose of the second 4D CT scan may be higher than <NUM> % of the radiation dose of the first 4D CT scan, in particular higher than <NUM> % of the radiation dose of the first 4D CT scan, in particular equal to the radiation dose of the first 4D CT scan.

Since the adapted 4D CT data correspond to the second 4D CT scan, it is not required by the method to apply the second 4D CT scan to the anatomical region, neither explicitly nor implicitly. The second 4D CT scan may be understood as a fiction used for characterizing the adapted 4D CT data.

A scanned volume fraction of the anatomical structure may be reduced, in particular significantly reduced, for the partial 4D CT scan compared to the first 4D CT scan. Throughout this specification, significantly reduced may be understood as reduced by a factor of <NUM>, in particular reduced by a factor of <NUM>, for example reduced by a factor of <NUM>. The scanned volume fraction of the second 4D CT scan may be comparable, in particular essentially equivalent, in particular equivalent, to the scanned volume fraction of the first 4D CT scan. To generate the supplementary 4D CT data, a partial 4D CT scan of only the most relevant regions, for example those regions that contain the tumor, may be done.

A scan range of the partial 4D CT scan may be selected based on the initial 4D CT data, the scan range of the partial 4D CT scan being reduced, in particular significantly reduced, compared to a scan range of the first 4D CT scan. The scan range of the second 4D CT scan may be comparable, in particular essentially equivalent, in particular equivalent, to the scan range of the first 4D CT scan. To reduce the volume fraction that is scanned and therefore irradiated during the partial 4D CT scan one possible way would be to reduce the scan range of the 4D CT scan and to adjust it so that only the region of tumor motion is irradiated during the scan.

An extent of an irradiation field along an x-ray fan direction may be reduced, in particular significantly reduced, for the partial 4D CT scan compared to the first 4D CT scan. The extent of the irradiation field along the x-ray fan direction of the second 4D CT scan may be comparable, in particular essentially equivalent, in particular equivalent, to the extent of the irradiation field along the x-ray fan direction of the first 4D CT scan. If the used CT scanner is capable of adjusting its irradiation field also along the fan direction this would be another source of possible radiation reduction potential. In this case the first 4D CT scan may be used in order to do a detruncation of the partial 4D CT scan.

Once the partial 4D CT scan with reduced irradiation range has been done it is proposed to combine the supplementary 4D CT data with the initial 4D CT data. Thereby the tumor region in the initial 4D CT data may be replaced and/or updated by the supplementary 4D CT data. To adjust the initial 4D CT data and the supplementary 4D CT data in the transition regions, a non-rigid registration or any other suited image registration algorithm can be used.

A scanned fraction of a breathing cycle may be reduced, in particular significantly reduced, for the partial 4D CT scan compared to the first 4D CT scan. The scanned fraction of the breathing cycle of the second 4D CT scan may be comparable, in particular essentially equivalent, in particular equivalent, to the scanned fraction of the breathing cycle of the first 4D CT scan. In particular, the breathing cycle may be the breathing cycle of the patient. For example, the partial 4D CT scan may be applied to a fraction of the breathing cyle, in particular only to the exhalation or to the inhalation phase, but to a scan range of the partial 4D CT scan that is equivalent to the scan range of the first 4D CT scan.

The adapted 4D CT data may be calculated based on the initial 4D CT data and the supplementary 4D CT data by applying an image registration, in particular a non-rigid transformation, from a given phase of the breathing cycle scanned during the first 4D CT scan to its corresponding phase in the part of the breathing cycle that was skipped during the partial 4D CT scan. Thereby the missing parts on the breathing cycle in the partial 4D CT scan, can be filled out to obtain the adapted 4D CT data covering the whole breathing cycle. Thereby, the image information regarding the missing phase is taken from the original full quality 4D CT. The breathing signal for the adapted 4D CT data can be either acquired in full during, before and/or after the partial 4D CT scan. Another option is to acquire a partial breathing signal covering only the scanned fraction of the breathing cycle of the partial scan and use it to calculate the missing part of the breathing signal, for example, based on the assumption, that an inhalation movement is essentially reverse to the exhalation movement.

The partial 4D CT scan may be a prospective phase selective 4D CT scan of a single phase of the breathing cycle. In particular, the prospective phase selective 4D CT scan may be a prospectively triggered phase selective 4D CT scan. In this case the 3D volume information would be taken from the supplementary 4D CT data while the information of the breathing motion would be taken form the initial 4D CT data.

A motion vector field of a breathing motion of the anatomical structure may be calculated based on the initial 4D CT data, wherein the adapted 4D CT data is calculated based on the motion vector field and the supplementary 4D CT data, in particular the supplementary 4D CT data for the single phase of the breathing cycle. The motion vector field of the breathing motion may be calculated based on the initial 4D CT data and used for calculating the adapted 4D CT data based on the supplementary 4D CT data resulting from the partial 4D CT scan of the single phase. By using the information from the initial 4D CT data the whole motion vector filed of the breathing motion can be computed which allows to transform each phase into each other phase of the cycle.

An initial radiation treatment planning data regarding the anatomical structure may be calculated based on the initial 4D CT data and/or an adapted radiation treatment planning data regarding the anatomical structure may be calculated based on the adapated 4D CT data.

The invention further relates to a computer program product or a computer-readable storage medium, comprising instructions which, when the instructions are executed by a computer, cause the computer to carry out the method according to one of the aspects of the invention.

The invention further relates to a data processing system, comprising a data interface and a processor, the data processing system being configured for carrying out the method according to one of the aspects of the invention.

The invention further relates to a medical imaging device, comprising the data processing system according to one of the aspects of the invention and being configured for carrying out the first 4D CT scan relating to the anatomical structure to obtain the initial 4D CT data and/or for carrying out the partial 4D CT scan relating to the anatomical structure to obtain the supplementary 4D CT data.

The medical imaging device may be, for example, a computed tomography device and/or a cone beam CT device.

The invention further relates to a radiation treatment planning system, comprising the data processing system according to one of the aspects of the invention and being configured for providing the initial radiation treatment planning data regarding the anatomical structure and/or for providing the adapted radiation treatment planning data regarding the anatomical structure.

Any of the algorithms and/or models mentioned herein can be based on one or more of the following architectures: deep convolutional neural network, deep belief network, random forest, deep residual learning, deep reinforcement learning, recurrent neural network, Siamese network, generative adversarial network or auto-encoder.

The computer program product can be, for example, a computer program or comprise another element apart from the computer program. This other element can be hardware, for example a memory device, on which the computer program is stored, a hardware key for using the computer program and the like, and/or software, for example, a documentation or a software key for using the computer program. A computer-readable storage medium can be embodied as non-permanent main memory (e.g. random-access memory) or as permanent mass storage (e.g. hard disk, USB stick, SD card, solid state disk).

The data processing system can comprise, for example, at least one of a cloud-computing system, a distributed computing system, a computer network, a computer, a tablet computer, a smartphone or the like. The data processing system can comprise hardware and/or software. The hardware can be, for example, a processor system, a memory system and combinations thereof. The hardware can be configurable by the software and/or be operable by the software. Calculations for performing an action of a method may be carried out in the processor.

Data, in particular the initial 4D CT data and the supplementary 4D CT data, can be received, in particular received through a data interface, for example, by receiving a signal that carries the data and/or by reading the data from a computer memory and/or by a manual user input, for example, through a graphical user interface. Data, in particular the adapted 4D CT data and/or radiation treatment planning data, can be provided, in particular provided through a data interface for example, by transmitting a signal that carries the data and/or by writing the data into a computer memory and/or by displaying the data on a display.

In the context of the present invention, the expression "based on" can in particular be understood as meaning "using, inter alia". In particular, wording according to which a first feature is calculated (or generated, determined etc.) based on a second feature does not preclude the possibility of the first feature being calculated (or generated, determined etc.) based on a third feature.

Reference is made to the fact that the described methods and the described systems are merely preferred example embodiments of the invention, and that the invention can be varied by a person skilled in the art, without departing from the scope of the invention as it is specified by the claims.

The invention will be illustrated below with reference to the accompanying figures using example embodiments. The illustration in the figures is schematic and highly simplified and not necessarily to scale.

<FIG> shows a flow chart for a computer-implemented method for providing adapted 4D CT data.

<FIG> shows the anatomical structure N comprising the lesion L. The irradiation field RL of the partial 4D CT scan is significantly reduced compared to the irradiation field R of the first 4D CT scan. The scan range of the first 4D CT scan is the extent of the irradiation field R along the scan direction Z. The scan range of the partial 4D CT scan is the extent of the irradiation field RL along the scan direction Z and significantly smaller than the scan range of the first 4D CTscan.

For the example shown in <FIG>, a radiation dose is reduced for the partial 4D CT scan compared to the first 4D CT scan, a scanned volume fraction of the anatomical structure N is reduced for the partial 4D CT scan compared to the first 4D CT scan, a scan range of the partial 4D CT scan is reduced compared to a scan range of the first 4D CT scan and an extent of an irradiation field along an x-ray fan direction X is reduced for the partial 4D CT scan compared to the first 4D CT scan.

<FIG> shows a breathing cycle diagram with the magnitud M over time T, covering the inhalation pahse PI, the exhalation phase PE and the single phases P1, P2, P3 and P4. The prospective phase selective 4D CT scan may be, for example, triggered prospectively, to cover the single phase P2 maximum inhalation state at the timepoint T2. In this case, a scanned fraction of the breathing cycle is reduced for the partial 4D CT scan compared to the first 4D CT scan, the first 4D CT scan covering the whole breathing cycle.

<FIG> shows the medical imaging device <NUM> in form of a computed tomography device, comprising the gantry <NUM>, the support frame <NUM>, the tilt frame <NUM>, the rotor <NUM>, the opening <NUM> for receiving the patient support structure <NUM>, the radiological interaction area <NUM>, the radiological interaction area <NUM> being located within the opening <NUM>, the radiation source <NUM> for generating the x-ray fan <NUM> and the radiation detector <NUM>. The medical imaging device <NUM> further comprises the patient table <NUM>, the patient table <NUM> comprising the patient table socket <NUM> and the patient support structure <NUM> in form of a patient table board. The patient table structure <NUM> is movably mounted on the patient table socket <NUM> along the system axis AS of the radiological interaction area <NUM>. The patient <NUM> is located on the patient support structure <NUM>.

Claim 1:
A computer-implemented method for providing adapted 4D CT data, the method comprising:
- Receiving (S1) initial 4D CT data, the initial 4D CT data corresponding to a first 4D CT scan, the first 4D CT scan relating to an anatomical structure (N) on a first examination date,
- Receiving (S2) supplementary 4D CT data, the supplementary 4D CT data corresponding to a partial 4D CT scan, the partial 4D CT scan relating to the anatomical structure (N) on a second examination date,
- Calculating (S3) the adapted 4D CT data based on the initial 4D CT data and the supplementary 4D CT data, the adapted 4D CT data corresponding to a second 4D CT scan, the second 4D CT scan relating to the anatomical structure (N) on the second examination date,
- Providing (S4) the adapted 4D CT data.