DOSE ERROR DETERMINATION DEVICE

Abstract

A dose error determination device (100) for forecasting radiation dose error for a body volume comprising one or more regions of interest subject to radiation treatment based on a dose plan, the dose error determination device comprising a dose-error determining unit (106) configured to generate, using dose plan data for the respective region of interest and an input value of the spatial-error quantity, dose variation data indicative of a rate of change of the dose values in a respective modified region of interest that in comparison with the respective region of interest is expanded in volume by an amount corresponding with the value of the spatial-error quantity and to determine and provide a respective value of a dose-error quantity associated with the respective region of interest, using a calculation rule representing a positive correlation of the dose-error quantity with the determined dose variation data.

Claims

1. A dose error determination device (100) for forecasting radiation dose error for a body volume comprising one or more regions of interest subject to radiation treatment based on a dose plan, the dose error determination device comprising: a dose plan (102) unit configured to provide dose plan data indicative of dose values associated with voxels of a current image of the body volume comprising voxels associated with the region of interest; an input unit (104) configured to request and receive user input indicative of a value of a spatial-error quantity corresponding to an amount of a spatial error of voxel coordinates in the current image associated with corresponding features of the body volume; a dose-error determining unit (106), which is configured: to generate, using the dose plan data for the respective region of interest and the value of the spatial-error quantity, dose variation data indicative of a rate of change of the dose values in a respective modified region of interest that in comparison with the respective region of interest is expanded in volume by an amount corresponding with the value of the spatial-error quantity; and to determine and provide a respective value of a dose-error quantity associated with the respective region of interest, using a calculation rule representing a positive correlation of the dose-error quantity with the determined dose variation data; and an output unit (110), which receives the respective value of the dose-error quantity, and is configured to provide an output indicative thereof.

2. The dose error determination device of claim 1, wherein the dose-error determining unit is configured to determine, for each voxel of the modified region of interest, local dose variation data representing a product of an amount of a local rate of change of the current dose values associated with the given voxel and of the value of the spatial-error quantity, and to determine the dose variation data associated with the region of interest as a maximum amount of the product within the modified region of interest.

3. The dose error determination device of claim 2, wherein the dose-error determining unit is further configured to identify a maximum dose value among the dose plan data, and, upon determining that the identified maximum dose value is smaller in amount than the determined maximum of the product within the modified region of interest, to provide to the output unit the identified maximum dose value as the respective value of the dose-error quantity associated with the respective region of interest.

4. The dose error determination device of claim 1, wherein the dose-error determining unit is further configured to determine as the dose variation quantity a maximum dose value and a minimum dose value among those dose values corresponding to voxels located within a distance given by the spatial-error quantity with respect to any voxel associated with each region of interest.

5. The dose error determination device of claim 1, wherein the input unit is further configured to request and receive dose-tolerance user input indicative of a tolerance interval of the dose-error quantity associated with a given region of interest; the dose-error determining unit is further configured: to receive the tolerance interval; and to determine, additionally using the tolerance interval, a relation between the determined value of the dose-error quantity and the tolerance interval associated with the given region of interest; and wherein the output unit is configured to provide the output as additionally being indicative of the determined relation.

6. The dose error determination device of claim 1, further comprising a statistics unit (108) storing statistical population data associating, based on a statistical population of previous measurements, statistical values associated with the spatial-error quantity to respective regions of interest; wherein the input unit is configured to request and receive user input indicative of at least one region of interest and, in response to receiving such user input, to access the statistics unit and to ascertain the statistical values associated with the spatial-error quantity for those regions of interest indicated by the user input, and to subsequently provide the request for user input indicative of the value of the spatial-error quantity in association with an output indicative of the ascertained respective statistical value.

7. The dose error determination device of claim 1, further comprising a dose-objective input interface for receiving dose-objective data for the region of interest indicative of desired values of dose-objective quantities associated with the previous dose plan; wherein the dose-error determining unit is additionally configured, using the dose-plan data and the determined value of the dose-error quantity for the region of interest, to generate dose-forecast data for the region of interest indicative of forecast values of the dose-objective quantities; and wherein the output unit is configured to provide the output as additionally being indicative of the dose-objective data and of the dose-forecast data.

8. The dose error determination device of claim 1, further comprising a ROI modelling unit, which is configured to generate, in response to a selection instruction received via the input unit, second instance region of interest data associated with a given one of the one or more regions of interest by modifying, in accordance with a selected one of a set of one or more respective uncertainty models defining spatial coordinate transformation instructions for transforming the region of interest only in regard to its spatial voxel coordinates, thus providing a representation of a transformed region of interest; wherein the dose-error determining unit is additionally configured to determine and provide an expected value of the dose-error quantity associated with the transformed region of interest; and wherein the input unit is additionally configured to request and receive user input indicative of the uncertainty model to be used by the ROI modelling unit.

9. The dose error determination device of claim 1, wherein the output unit is configured to associate a color-code value to the received value of the dose-error quantity, in accordance with a predetermined color code assigning different colors to different predetermined value intervals of the dose-error quantity, and to generate and provide the output as additionally being indicative of the color assigned to the respective value of the dose-error quantity.

10. The dose error determination device of claim 8, wherein the output unit is additionally configured to receive two-dimensional image data representing an image of the respective region of interest, and to generate and provide the output of the dose-error quantity in the form of a graphical overlay onto the image of the respective region of interest.

11. The dose error determination device of claim 1, wherein: the dose plan unit is configured to provide a plurality of dose plans, each comprising respective dose plan data associated with alternative dose plans for the region of interest; wherein the dose-error determining unit is further configured to provide plan-robustness data indicative of a respective plan-robustness value for each dose plan and in dependence of the received value of the spatial-error quantity, the plan-robustness value being determined in accordance with a predetermined rule based on the determined values of the dose-error quantities associated with the one or more regions of interest; and wherein the output unit is further configured to receive the plan-robustness data and to provide an output indicative thereof.

12. A computer-implemented dose error determination method for forecasting radiation dose error for a body volume comprising one or more regions of interest subject to radiation treatment based on a dose plan, the dose error determination method comprising: providing dose plan data indicative of dose values associated with voxels of a current image of the body volume comprising voxels associated with the region of interest; requesting and receiving user input indicative of a value of a spatial-error quantity corresponding to an amount of a spatial error of voxel coordinates in the current image associated with corresponding features of the body volume; generating, using the dose plan data for the respective region of interest and the value of the spatial-error quantity, dose variation data indicative of a rate of change of the dose values in a respective modified region of interest that in comparison with the respective region of interest is expanded in volume by an amount corresponding with the value of the spatial-error quantity; determining and providing a respective value of a dose-error quantity associated with the respective region of interest, using a calculation rule representing a positive correlation of the dose-error quantity with the determined dose variation data; and providing an output indicative the respective value of the dose-error quantity.

13. A computer program comprising instructions which, when the program is executed by a computer, cause the computer to carry out the method of claim 12.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0046] In the following drawings:

[0047] FIG. 1 shows a schematic representation of an embodiment of a dose error determination device.

[0048] FIG. 2A shows a first image of a body volume that includes a region of interest and which is divided in voxels, each of which is associated to a radiation dose value.

[0049] FIG. 2B shows a second image of the body volume that includes the region of interest showing a different shape when compared to that of the first image.

[0050] FIG. 3 shows an example of an informative table displayed by a display unit used in combination with a dose error determination device.

[0051] FIG. 4 shows an example of a sensitivity map displayed by a display unit used in combination with a dose error determination device.

[0052] FIG. 5 shows an example of a graph plotting values of the dose-error quantity versus values of spatial-error quantities for a given region of interest.

[0053] FIG. 6 shows an example of another informative table displayed by a display unit used in combination with a dose error determination device.

[0054] FIG. 7 shows a schematic representation of another embodiment of a dose error determination device.

[0055] FIG. 8 shows a schematic representation of another embodiment of a dose error determination device.

DETAILED DESCRIPTION OF EMBODIMENTS

[0056] Before turning to a description of the enclosed drawings, some disclosure on considerations underlying the present invention will be given in the following.

[0057] In radiotherapy, the statistics of the dose delivered to an ROI is summarized and presented to the user in a graphical form, e.g., dose volume histogram, or informative table containing dose parameters. In order to be able to calculate the dose statistics, the ROI is represented by a set of voxels. For each voxel, the value of the dose at that voxel is interpolated from a 3D dose volume. The uncertainty (due to spatial errors) in estimating the dose at an ROI voxel with coordinates (x.sub.i, y.sub.i, z.sub.i) can be quantified by the difference between the dose d at the position (x.sub.i, y.sub.i, z.sub.i) and the dose d at the “true” voxel position ({circumflex over (x)}.sub.i, ŷ.sub.i, {circumflex over (z)}.sub.i). The difference between ({circumflex over (x)}.sub.i, ŷ.sub.i, {circumflex over (z)}.sub.i) and ({circumflex over (x)}.sub.i, ŷ.sub.i, {circumflex over (z)}.sub.i) is the spatial error vector at voxel i

(e.sub.x,i,e.sub.y,i,e.sub.z,i)=(x.sub.i,y.sub.i,z.sub.i)−({circumflex over (x)}.sub.i,ŷ.sub.i,{circumflex over (z)}.sub.i).  (1)

[0058] In the following, the magnitude of the error vector is denoted by r. For the case in which the spatial errors are due to DIR inaccuracies, determining the “true” voxel position requires manual editing to determine ({circumflex over (x)}.sub.i, ŷ.sub.i, {circumflex over (z)}.sub.i) or, equivalently, it requires the error vector. In clinical practice, however, the true voxel position or the error vector, are not available.

[0059] The embodiments of the dose error determination device and method disclosed herein allow calculating in an efficient way the impact of the magnitude of the contour mapping errors on dose parameters. The proposed solution consists of several components, which will be described in more abstract form in the following and elucidated further below more specifically when the description turns to the enclosed drawings:

[0060] i) For a user-selected value of magnitude of error r, an output unit such as a graphical user interface (GUI) informs the user on the values of the upper bounds of the maximum dose change for each ROIs. The value of r can be provided by the user as a numeric value and represents a user estimate of the maximum error magnitude for an ROI. In addition, for each ROI the GUI can suggest a range of r values from previous studies on population data.

[0061] For example, an upper bound for the dose difference d(x.sub.i, y.sub.i, z.sub.i)−d({circumflex over (x)}.sub.i, ŷ.sub.i, {circumflex over (z)}.sub.i) can be established by using the mean value theorem. In detail, the mean value theorem for the case of functions with three variables f and with real values, i.e., f: D.fwdarw., where D is a subset of .sup.3, states that if D is an open and connected set and f is continuous and differentiable on D then, for any two points (x.sub.i, y.sub.i, z.sub.i) and ({circumflex over (x)}.sub.i, ŷ.sub.i, {circumflex over (z)}.sub.i) such that the line segment L uniting (x.sub.i, y.sub.i, z.sub.i) and ({circumflex over (x)}.sub.i, ŷ.sub.i, {circumflex over (z)}.sub.i) belongs to D, there is a point (a, b, c)∈L such that

f(x.sub.i,y.sub.i,z.sub.i)−f({circumflex over (x)}.sub.i,ŷ.sub.i,{circumflex over (z)}.sub.i)=∇f(a,b,c).Math.((x.sub.i,y.sub.i,z.sub.i)−({circumflex over (x)}.sub.i,ŷ.sub.i,{circumflex over (z)}.sub.i)),  (2)

[0062] where ∇f(a, b, c)∈.sup.3 is the gradient of f at (a, b, c) and “.Math.” is the scalar product between two vectors.

[0063] From the Cauchy-Schwartz's inequality it follows that

|f(x.sub.i,y.sub.i,z.sub.i)−f({circumflex over (x)}.sub.i,ŷ.sub.i,{circumflex over (z)}.sub.i)|≤∥∇f(a,b,c)∥∥(x.sub.i,y.sub.i,z.sub.i)−({circumflex over (x)}.sub.i,ŷ.sub.i,{circumflex over (z)}.sub.i)∥,  (3)

where ∥ ∥ denotes the Euclidian norm on .sup.3.

[0064] Since the dose distribution d satisfies the conditions of the mean value theorem, by applying inequality (2) it follows that for any point (x, y, z) within a sphere centered at (x.sub.i, y.sub.i, z.sub.i) and with radius r that

[00001]$\begin{array}{cc}.Math.d\left(x,y,z\right)-d\left(x_{i.Math.\prime }.Math.y_i,z_i\right).Math.\le \underset{\left(x,y,z\right)}{\max }.Math..Math.\nabla d\left(x,y,z\right).Math..Math.r,.Math.& \left(4\right)\end{array}$

[0065] Therefore, for an ROI for which (as an example) the maximum DIR uncertainty is smaller than or equal to r, the following inequality holds for the maximum dose change (mDC)

[00002]$\begin{array}{cc}m.Math.D.Math.C\le \min (\underset{\left(x,y,z\right)\in R.Math.O.Math.I_{-}.Math.r}{\max }.Math..Math.\nabla d\left(x,y,z\right).Math..Math.r,\underset{\left(x,y,z\right)\in D}{\max }.Math.d)& \left(5\right)\end{array}$

[0066] where ROI_r denotes a volume obtained by uniformly expanding the ROI volume with r and D is the dose grid. Here we denote the right hand side of inequality (5) by “upper bound” (UB).

[0067] Note that inequality (5) holds not only for spatial errors that can be described as displaced voxel position (e.g., from the true position ({circumflex over (x)}.sub.i, ŷ.sub.i, {circumflex over (z)}.sub.i) to position (x.sub.i, y.sub.i, z.sub.i) but also for spatial errors that result in missing or extra voxels up to a distance r from the boundary of the “true” ROI.

[0068] The following description now turns to the enclosed drawings.

[0069] FIG. 1 shows a schematic representation of an embodiment of a dose error determination device 100 for forecasting radiation dose error for a body volume comprising one or more regions of interest subject to radiation treatment based on a dose plan. The explanation of the dose error determination device will be done with further reference to FIGS. 2A and 2B which show a first image 200 and a second image 201 of the same body volume. The images show a respective region of interest 204, 205, which is associated to a different set of voxels. Each voxel is additionally associated to respective dose value d.sub.xy in accordance with a dose plan. The dose error determination device comprises a dose plan unit 102 configured to provide dose plan data indicative of dose values associated with voxels of a current image of the body volume 200 comprising voxels (d.sub.33, d.sub.34, d.sub.43, d.sub.44) associated with the region of interest (ROI) 204. The dose error determination device 100 also comprises an input unit 104, that is configured to request and receive user input indicative of a value of a spatial-error quantity corresponding to an amount of a spatial error of voxel coordinates in the current image associated with corresponding features of the body volume. For instance, a use who has access to the first image 200 and to the second image 201 of the body volume identifies that between the ROI 204 and the ROI 500, there is a spatial error or misalignment. The user then can manually input using the input unit the value of the value of a spatial-error quantity, which is r in the case of FIGS. 2A and 2B, as a numerical value. Additionally, some dose error determination devices comprise a statistics unit 108 that stores statistical population data associating, based on a statistical population of previous measurements, statistical values associated with the spatial-error quantity to respective regions of interest. The input unit is in these particular dose error determination devices configured to request and receive user input indicative of at least one region of interest and, in response to receiving such user input, to access the statistics unit and to ascertain the statistical values associated with the spatial-error quantity for those regions of interest indicated by the user input, and to subsequently provide the request for user input indicative of the value of the spatial-error quantity in association with an output indicative of the ascertained respective statistical value.

[0070] Regardless of whether the dose error determination device includes a statistics unit or not, it comprises a dose-error determining unit 106 that is configured to receive the dose plan data and the value of the spatial error quantity r and to generate dose variation data indicative of a rate of change of the dose values d.sub.xy in a respective modified region of interest 207 that in comparison with the corresponding region of interest 205 is expanded in volume by an amount corresponding with the value of the spatial-error quantity r. The dose-error determining unit is also configured to determine and provide a respective value of a dose-error quantity associated to the region of interest. This is done by using a calculation rule that represents a positive correlation of the dose-error quantity with the determined dose variation data. This calculation rule involves in some particular dose-determination unit a multiplication operation between the dose variation data for each voxel with the value of the spatial-error quantity. For instance, in some dose error determination devices in accordance with the present invention, the error determination unit is configured to determine, for each voxel of the modified region of interest, local dose variation data representing a product of an amount of a local rate of change of the current dose values associated with the given voxel and of the value of the spatial-error quantity, and to determine the dose variation data associated with the region of interest as a maximum amount of the product within the modified region of interest. Other calculation rules comprise a multiplication of the dose variation data with values obtained using a monotonically increasing function, so that for increasing values of the dose variation data, the resulting dose-error quantity does not decrease. In some advantageous dose error determination devices and independently on the calculation rule used, the dose-error determining unit is further configured to determine as the dose variation quantity a maximum dose value and a minimum dose value among those dose values corresponding to voxels located within a distance given by the spatial-error quantity with respect to any voxel associated with each region of interest.

[0071] The dose error determination device also comprises an output unit 110 which receives from the dose-error determination unit the respective value of the dose-error quantity of the one or more ROIs and is configured to provide an output indicative thereof.

[0072] Advantageously, the dose error determination unit is used in combination with a display unit that is configured to receive from the output unit 110 the output indicative of the dose error quantity of the one or more ROIs. The display unit may comprise a graphical user interface configured to display the data received from the output unit in a way which enables the user to focus on the most critical ROIs in dependence on the dose plan and the determined dose-error quantities. Depending on the actual information content of the output, the graphical user interface may be configured to displays the output data in different ways.

[0073] For instance, an exemplary graphical user interface that can be used in combination with any of the dose error determination devices in accordance with the invention is configured to display the output data in the form of an informative table, listing the one or more ROIs in a predetermined order, such as in an increasing or decreasing order of the associated dose-error quantity. An example of an informative table displayed at the displayed unit is shown in FIG. 3. The figure shows an informative table presenting a list of ROIs A, B, C and D together with their respective determined dose-error quantities V.sub.DEQ for a given value of the spatial error quantity, which is this particular case is 3 mm.

[0074] A user can select how the list is to be sorted, i.e. in an increasing or a decreasing order of the determined dose-error quantities, which are indicative of the maximum dose change expected at the ROI for the given value of the spatial error quantity. By providing such a table, the user might decide to skip manual editing for the ROIs for which, for example, the estimated impact of contour inaccuracies given by the value of the spatial error quantity on the dose parameters is small. Similarly, the user could choose to manually review the ROIs for which small contour mapping errors result in large dose changes, as given by the associated value of the dose-error quantity. Note that the value of the dose-error quantity is a measure of sensitivity for all voxels of a given ROI, and not only for the voxels with maximum dose.

[0075] In the case of dose error determination devices that include an input unit further configured to request and receive dose-tolerance user input indicative of a tolerance interval of the dose-error quantity associated with a given region of interest, the user can provide thresholds or ranges for accepted values of maximum dose changes (i.e. values of dose-error quantities). In an informative table such as that of FIG. 3, the ROIs and their corresponding values of dose-error quantities can be advantageously provided in accordance with a predetermined color coding, such as for instance a traffic light color coding with red yellow and green colors.

[0076] Some dose error determination devices are suitably configured to determine the values of dose-error quantity for one or more ROIs and for a plurality of values of the spatial-error quantity. These dose error determination devices can be advantageously used in combination with a display unit configured to generate a sensitivity map, such as the one shown in FIG. 4. The sensitivity map of FIG. 4 includes a listing of ROIs, A-G, in a vertical axis and a sequence of values of the spatial-error quantity, in this case a magnitude of spatial error due to inaccuracies in a deformable image registration, in a horizontal axis. The dose error determination device determines the for each ROI and for each value of the spatial error quantity the corresponding value of the dose-error quantity. The display unit is then advantageously configured to display the output data as a sensitivity map using a predetermined color coding, wherein in color represents a range of the values of dose error quantity V.sub.DEQ.

[0077] Another example of the display unit can be alternatively or additionally configured to display the output data as a graph plotting, for one or more ROIs, the value of the dose-error quantity, for example in a vertical axis, versus the value of the spatial error quantity in the horizontal axis, as it is exemplarily shown in FIG. 5.

[0078] Dose error determination devices that are configured to determine as the dose variation quantity a maximum dose value and a minimum dose value among those dose values corresponding to voxels located within a distance given by the spatial-error quantity with respect to any voxel associated with each region of interest can be advantageously used in combination with a display unit configured to display an upper and a lower bound dose volume histogram (DVH) for a given ROI and a given value of the spatial-error quantity. Additionally, upper and lower bounds of dose value parameters inferred from the dose plan such as a mean dose value for a given ROI or a value of a fractional volume indicative of that volume fraction for which an estimated received radiation is higher than a predetermined radiation threshold, can be provided also in the form of an informative table.

[0079] Some display units are also configured to display an interactive graph that allows the user to interactively inspect all values of the dose-error quantity for a specific value of the spatial-error quantity. For instance, such a display unit can be configured to provide the value of the dose-error quantity for a given value of the spatial-error quantity, or alternatively or additionally, a maximum value of tolerated spatial-error quantity such that the value of the spatial-error quantity satisfies a predetermined constrain, such as a maximum allowed value thereof. These displays units are advantageously used with dose error determination devices that include a dose-objective input interface for receiving dose-objective data for the region of interest indicative of desired values of dose-objective quantities associated with the dose plan. In these dose error determination devices, the dose-error determining unit is additionally configured, using the dose-plan data and the determined value of the dose-error quantity for the region of interest, to generate dose-forecast data for the region of interest indicative of forecast values of the dose-objective quantities; and the output unit is configured to provide the output as additionally being indicative of the dose-objective data and of the dose-forecast data.

[0080] Another example of a graphical user interface of a display unit that can be used in combination with a dose error determination device in accordance with the present invention is shown in FIG. 6. The table shown in FIG. 6 includes a first column with the list of the ROIs, A-F. It also shows the objectives O for each ROI. The objectives include the information pertaining to a type of value of dose-error quantity (e.g. 1 being a maximum value of DVH, 2 being a mean dose value, 3 being a percentage of the maximum DVH), to the desired dose value D in accordance with the dose plan and to a volume value V, either in terms of absolute volume or relative volume. The list of objectives is may be automatically imported from a treatment plan in Pinnacle, or the user could manually fill in the objectives. For each ROI, the graphical user interface will indicate whether for a certain range of DIR errors, also given in the table of FIG. 6 as r(cm), the objectives are met (ok), or not met (no). The user could decide to skip review of ROIs that are robust to a large range of DIR errors and instead review the ROIs that are sensitive to DIR uncertainties. The names of ROIs that are relatively more sensitive to spatial errors could be highlighted by, for instance displaying them in a larger font, or displaying them in a different font color, or intermittently displaying them with a blinking pattern, etc.)

[0081] Yet another display unit is advantageously configured to enable a robustness evaluation of the dose parameters against values of spatial-error quantities such as DIR uncertainties by applying a user-selected model of uncertainties by means of a dedicated graphical user interface. A model of uncertainty is a parametric model that modifies the physical coordinates of the ROI's voxels, thus producing a second instance of the ROI. Several uncertainty models can be provided, such as for example, worst case scenario DVH, rotations around the three axis, translations, shrinking or expanding the ROI with margins, combination of translations with rotations, random perturbations of the ROI surface, parametric models of errors learned from previous data using principal component analysis, or any combination of the previously mentioned models. The user could select the desired uncertainty model from a drop-down menu. For each uncertainty model, the user can input parameter values or select a range of values using for instance a slider. The value of the dose-error quantity can be calculated for each selected uncertainty model and value(s) of spatial-error quantity. The results of the robustness evaluation will be presented, for example, in the form of a figure displaying the dose volume histograms corresponding to the selected uncertainty model, and baseline DVH (e.g., before applying the DIR error). The user can also be presented with a table summarizing, for instance, dosimetric objectives for each selected ROI, or baseline value of the objective or, the objective value for the selected value of DIR error, or any combination thereof. A traffic light system can for example be used to notify the user whether the objective for the selected DIR error value is met (green), equal (yellow), or not met (red).

[0082] This display unit is advantageously used in combination with a dose error determination device such as the dose error determination device 700 shown in FIG. 7. The dose error determination device 700 comprises a ROI modelling unit 712, which is configured to generate, in response to a selection instruction received via the input unit 704, second instance region of interest data associated with a given one of the one or more regions of interest by modifying, in accordance with a selected one of a set of one or more respective uncertainty models defining spatial coordinate transformation instructions for transforming the region of interest only in regard to its spatial voxel coordinates, thus providing a representation of a transformed region of interest. In the dose error determination device 700, the dose-error determining unit 706 is additionally configured to determine and provide an expected value of the dose-error quantity associated with the transformed region of interest, and the input unit 704 is additionally configured to request and receive user input indicative of the uncertainty model to be used by the ROI modelling unit.

[0083] Yet another display unit is advantageously configured to offer the user a sensitivity tool configured to analyze plan robustness to spatial errors, such as, but not limited to, ROI contouring errors or geometric image artifacts. This display unit can advantageously be used to compare rival radiation plans for a patient and thus assist in a choice of radiation plan. This analysis can be performed manually by the expert or in automated mode. Furthermore, the results of such sensitivity analysis could be taken as an input in a further optimization process to generate plans robust to contouring errors. For instance, two different radiation plans A and B for a given patient P can be compared in terms of robustness to spatial errors of an ROI in the following way: for each plan A and B, a plurality of values of the spatial-error quantity are applied and the corresponding value of the dose-error quantity associated to plan A and plan B is calculated. The value of the dose-error quantity is in a particular example a standard deviation of a fractional ROI volume receiving dose higher than a threshold dose value v. In another example it is indicative of the width of the DVH band a certain value of the dose The width of the DVH bands for two plans can be shown to the user as numerical quantities or displayed in a graphical way.

[0084] This display unit is advantageously used in combination with a dose error determination device such as the dose error determination device 800 shown in FIG. 8. The dose error determination device 800 comprises a dose plan unit 802 that is configured to provide a plurality of dose plans, each comprising respective dose plan data associated with alternative dose plans for the region of interest. The dose-error determination unit 806 is further configured to provide plan-robustness data indicative of a respective plan-robustness value for each dose plan and in dependence of the received value of the spatial-error quantity, the plan-robustness value being determined in accordance with a predetermined rule based on the determined values of the dose-error quantities associated with the one or more regions of interest. Also, the output unit 810 is further configured to receive the plan-robustness data and to provide an output indicative thereof.

[0085] In summary, a dose error determination device for forecasting radiation dose error for a body volume comprising one or more regions of interest subject to radiation treatment based on a dose plan in presented. The dose error determination device comprises a dose-error determining unit configured to generate, using dose plan data for the respective region of interest and an input value of the spatial-error quantity, dose variation data indicative of a rate of change of the dose values in a respective modified region of interest that in comparison with the respective region of interest is expanded in volume by an amount corresponding with the value of the spatial-error quantity and to determine and provide a respective value of a dose-error quantity associated with the respective region of interest, using a calculation rule representing a positive correlation of the dose-error quantity with the determined dose variation data.

[0086] In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality.

[0087] A single step or other units may fulfill the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to ad-vantage.

[0088] Any reference signs in the claims should not be construed as limiting the scope.