Method, computer program product and computer system for dose calculation
By combining fast and accurate dose calculation algorithms and selecting appropriate algorithms based on patient anatomical structure and material characteristics, the accuracy and speed of dose calculations in close-range radiation diagnosis and treatment are solved, and efficient dose calculations in clinical applications are achieved.
Patent Information
- Application Number
- CN202380043025.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Priority Date
- 2022-06-28
- Filing Date
- 2023-06-16
- Publication Date
- 2024-12-27
AI Technical Summary
The existing close-range radiation diagnosis and treatment dosage calculation methods are difficult to balance between accuracy and speed. The simplified algorithm is fast but inaccurate. Although the Monte Carlo algorithm is accurate, it is time-consuming and cannot meet the clinical optimization needs.
Using a combination of fast but less accurate dose calculation algorithms and more accurate but time-consuming algorithms, the appropriate algorithm is selected based on the patient's anatomical structure and material characteristics, and the algorithm selection is determined through heterogeneity index values and tissue density differences to achieve different Dynamic switching of dosage calculation method for regions.
Obtain accurate dosage calculation results within a reasonable calculation time, which improves the optimization efficiency and accuracy of the treatment plan and is suitable for clinical applications.
Smart Images
Figure CN119212763A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to radiotherapy treatment and more particularly to brachytherapy. Background Art
[0002] Unlike external beam radiotherapy, in which radiation is delivered to the patient from the outside in the form of a beam, brachytherapy involves inserting a radiation source into the patient's body or near a target volume. The radiation source can be in the form of a seed, a ribbon, or a capsule. Brachytherapy involves many advantages, including the ability to place the radiation source in close proximity to the target and have it remain in place relative to the target even if the entire patient moves or there is internal motion in the patient's body. It also allows for high dose rates, which enables treatment in only a few small sections.
[0003] In some forms of brachytherapy, a radiation source is placed inside the patient and moved through the patient's body by exploiting natural cavities or interstitial passages, usually inserted through one or more catheters. The radiation source moves through the passages and stops at predetermined positions along the trajectory, called dwell positions. The time spent in each dwell position (dwell time) is determined individually for each position and is typically on the order of 1 to 2 seconds.
[0004] For any type of radiotherapy, it is very important to calculate the resulting doses in different parts of the patient. This requires a lot of calculations, since the radiation source radiates in all directions from each dwelling position in the patient's body. In general, the known algorithms for such calculations are based on simplifying assumptions that make the calculations fast but not always accurate, or on more accurate but time-consuming dose engine calculations.
[0005] One method of calculating dose involves an analytical algorithm that uses the cylindrical symmetry of the dose distributed by the source. The algorithm is based on the assumption that the surrounding tissue is identical and homogeneous to water. This simplification means that the algorithm is fast but not necessarily accurate, particularly for tissues with heterogeneous properties or with material properties that differ greatly from water. Relevant material properties include density, effective electron density, photoelectric effect, and Compton scattering.
[0006] Another method of calculating dose involves Monte Carlo dose engines. Such dose calculations can be performed with high accuracy but are currently very time consuming and therefore may not be clinically applicable, especially when optimizing treatment plans. Summary of the invention
[0007] The purpose of the present disclosure is to provide a dose calculation method for brachytherapy, which is both accurate and fast compared with the prior art methods.
[0008] The present disclosure relates to a dose calculation method for brachytherapy treatment, wherein radiation is provided by one or more radiation sources from at least a first dwell position and a second dwell position in a patient, the radiation provided at each dwell position generating a dose contribution from the dwell position. The method includes selecting a first dose calculation algorithm to be used to calculate the dose contribution from the first dwell position and a second dose calculation algorithm to be used to calculate the dose contribution from the second dwell position, the second dose calculation algorithm being different from the first dose calculation algorithm, calculating the dose contribution from the first dwell position according to the first dose calculation algorithm and calculating the dose contribution from the second dwell position according to the second dose calculation algorithm, and calculating a total dose as the sum of the dose contributions from at least the first dwell position and the second dwell position.
[0009] This method enables an optimal combination of dose calculation methods in terms of time and accuracy, taking into account the patient's anatomy. The method identifies locations where a more complex algorithm is required for accurate results. A fast but less accurate algorithm can be used that will return satisfactory results. Thus, the method will return accurate values in complex areas and save time by using a faster method in areas where less accuracy is required (i.e., areas where the density of the surrounding tissue is close to water and shows little variation). Thus, satisfactory results can be obtained with reasonable calculation time.
[0010] The first dose calculation algorithm may be an analytical algorithm that assumes a uniform density of tissue around the first dwell position, such as the density of water. Such algorithms include ray tracing and TG43, which will be fast but not always very accurate.
[0011] The second dose calculation algorithm is preferably arranged to take into account heterogeneity. Such an algorithm will be slower but will yield more accurate results. Examples of such algorithms include the MC dose engine and the Boltzmann equation solver.
[0012] Preferably, the dose calculation algorithm for each dwell position is selected based on an index value indicating a difference in material properties (such as density between water and tissue surrounding the dwell position), or an index value indicating a change in material properties in tissue surrounding the dwell position, or a combination of the two. This will facilitate selection of an appropriate dose calculation algorithm for each dwell position.
[0013] The index value may be a heterogeneity index of the dwell position indicating variations in tissue properties in the volume surrounding the dwell position.A faster algorithm is selected for regions with low heterogeneity and a slower more accurate algorithm is used for regions with high heterogeneity.
[0014] A heterogeneity index may be calculated for each dwell location based on ray tracing in two or more directions about the dwell location and determining tissue properties of intersecting voxels for each ray tracing operation.
[0015] Alternatively, the heterogeneity index for each dwell position is calculated based on defining sub-volumes around each dwell position, each sub-volume comprising a plurality of voxels and determining tissue properties in at least some of the plurality of voxels. Changes in the tissue properties will indicate the degree of heterogeneity, such that large changes will result in a high heterogeneity index, while small changes or no changes will result in a low heterogeneity index.
[0016] Instead of, or in addition to, the heterogeneity index described above, the dose calculation method for each dwell position may be selected based on a comparison to a homogeneous reference material, such as water. This would also enable different dose calculation methods to be selected for different homogeneous tissues. Typically, tissue with a different density than the reference material will indicate that a more accurate dose calculation method should be used, even if the tissue has a low heterogeneity index.
[0017] More than two dose calculation algorithms can be used. For example, a fast, medium, and slow but accurate algorithm can be used for less critical, somewhat critical, and very critical areas, respectively. Typically, highly heterogeneous areas will be the most critical areas, while highly homogeneous areas can be handled using a fast algorithm.
[0018] The dose calculation method according to the present invention can be used in any suitable context, but is particularly useful for optimization. Therefore, the present disclosure also relates to a brachytherapy optimization method for optimizing a set of dwell times for a corresponding set of dwell positions. The brachytherapy optimization method includes calculating the total dose using a method according to any of the above embodiments and using the calculated total dose in the optimization process.
[0019] The present disclosure also relates to a computer program product arranged to perform a dose calculation according to a first dose calculation algorithm and a second dose calculation algorithm, the computer program product comprising computer readable code means which, when executed in a computing device, will cause the computing device to perform a method according to any one of the above embodiments. As is common in the art, the code means may be stored on a non-transitory memory. The present disclosure also relates to a computer comprising a processor and a program memory having such a computer program product stored therein so that it can be executed by the processor. BRIEF DESCRIPTION OF THE DRAWINGS
[0020] The present invention will be described in more detail below by way of examples and with reference to the accompanying drawings.
[0021] Figure 1Illustration shows a portion of a patient undergoing brachytherapy.
[0022] Figure 2 is a flow chart of a method according to an embodiment of the present invention.
[0023] Figure 3 and Figure 4 The diagram illustrates possible ways of calculating index values.
[0024] Figure 5 yes Figure 2 A more detailed flowchart of a portion of the flowchart in . DETAILED DESCRIPTION
[0025] Figure 1 The head of a patient 10 undergoing brachytherapy is illustrated, seen in cross-section, including a treatment site around a target 12 to be exposed to radiation. Three channels 14 are provided through which the radiation source will pass in a manner known in the art. As will be appreciated, there will typically be multiple channels, each with multiple dwell positions. For clarity, only three channels are shown here. The treatment plan includes multiple dwell positions within each channel 14, where the radiation source will temporarily stop, and a dwell time for each dwell position indicating how long the radiation source will stay at that position. The total dose will be the sum of the doses delivered from all dwell positions. Shielding (not shown) can be applied to block radiation in certain directions to protect organs at risk. As will be appreciated, the geometry of the treatment site is close to uniform in some areas and more non-uniform in other areas due to air cavities, bones, teeth, and possibly other materials. This will affect the dose delivered outwardly in different directions from the radiation source at different locations. How to achieve this is known in the art, including determining the dwell positions and the properties of the radiation source. The geometry of the radiation source also affects the dose in different directions. Therefore, the dose calculation algorithm for each dwell position may be selected based on the geometry of the treatment site and / or the geometry of the radiation source proximate to the dwell position.
[0026] In some embodiments, the fast but less accurate dose calculation algorithm is the commonly used analytical TG43 dose algorithm.Examples of accurate but slower dose calculation algorithms include dose engine algorithms, such as Monte Carlo based algorithms.
[0027] Figure 2 is a flow chart of a method according to an embodiment of the present invention. The method is performed after the target and any organs at risk S21 and a plurality of dwell positions within the treatment area S22 have been identified. This constitutes input data to the method.
[0028] The total dose generated from all dwell positions is required during treatment plan optimization, but is also required when calculating the final dose of the resulting treatment plan. The final dose is used to evaluate the prescription and clinical goals and approve the planned treatment for delivery. The accuracy requirements for the final dose are higher than the dose used during optimization. According to the present disclosure, two or more different dose calculation algorithms with different characteristics are used. For each dwell position, the most appropriate dose calculation algorithm is selected in step S23. The selection of the dose calculation algorithm for each dwell position can be based on any suitable set of criteria. In some embodiments, the selection is based on an index value indicating a difference in material properties, such as the density between water and tissue surrounding the dwell position, or a change in material properties in tissue surrounding the dwell position, or a combination of the two. How to determine the index value will be discussed in more detail below.
[0029] In step S24, the dose contribution from the source is calculated at each dwell position using the algorithm selected for that dwell position in step S23. In step S25, a dwell time is selected for each dwell position. In step S26, the total resulting dose is calculated as a weighted sum of all dose contributions calculated in step S24, the weighted sum being weighted by the corresponding dwell time in the dwell position obtained in step 25. The method may include calculating dose contributions from dwell positions belonging to a plurality of channels or cavities within the patient.
[0030] according to Figure 2 The method may be used as part of an optimization process, wherein the dwell time is used as an optimization variable in a dose-based optimization, and the dwell time is varied based on the performance of a user-specified optimization function that is equivalent on the total resulting dose. This is indicated by optional step S27, which will allow the method to repeat from step S25 until the optimization is terminated, which can occur, for example, when a predefined number of iterations is reached or when the optimization function has been performed, such as when a suitable total dose has been achieved.
[0031] Figure 3 A first method of calculating the above index value is illustrated. Reference numeral 31 indicates a channel through which the radiation source is to pass. A plurality of stop points 33 are defined within the channel. A stop point 33a is selected for illustration. For this selected stop point 33a, a plurality of directions ( Figure 3 ) and ray tracing is performed in these directions. Ray tracing involves tracing the ) for each intersecting voxel in the ray trajectory Cumulative. Appropriate tissue properties to consider include tissue density, effective electron density, and cross sections for the photoelectric effect or Compton scattering. Figure 3 In the , the obtained items are marked as , , Since the dose from the source in each dwell position decreases with increasing distance, this term preferably decreases with increasing distance from the dwell position to account for the fact that material changes close to the source will have a greater effect on the dose distribution than those further away from the source. The index value for the selected dwell point is calculated based on the results of these three ray trajectories as all ray trajectories Since the dwell locations are usually close to each other, it is also possible to calculate the index value for a group of adjacent dwell locations instead of calculating the index value for each dwell location one by one.
[0032] exist Figure 3 In the example in , the contribution from each ray trajectory to the index value can be expressed as Equation 1:
[0033] (1)
[0034] That is, in all voxels The difference between the tissue density and the water density of the voxel is divided by the voxel The distance from the center of the stop point Substituting for the difference in tissue density, Some other material property, or a combination of two or more properties, can be represented. The molecule can also be written as the relative difference in material properties between tissue and water. Additionally, more than one material property can be considered, in which case will be the sum of the relative differences in the set of material properties.
[0035] In this case, the total index value It can be expressed as Equation 2:
[0036] (2)
[0037] That is, for all selected ray tracing directions The sum of all index value contributions calculated according to Equation 1.
[0038] Alternatively, or in addition to the comparison with water, a comparison between tissue properties of different voxels within the volume of interest can be used as an indicator of heterogeneity. In this case, Equation 1 would be replaced by Equation 1a:
[0039] (1a)
[0040] in, Represents the variance of a material property or properties, i.e., the average across all ray-traced voxels.
[0041] If the tissue surrounding the dwell position is relatively homogeneous, it may still be desirable to select a more accurate dose calculation method. Thus, the selection of the dose engine may also be based on the difference in tissue density between the tissue surrounding the dwell position and a reference density value, wherein a difference exceeding a set threshold would indicate that a more accurate dose calculation method should be used. A suitable reference density value is typically the density of water.
[0042] Figure 4 A second method for determining the index value H is shown. Figure 3 As shown, a channel 41 is shown, which includes a plurality of dwell positions 43. In this case, a subvolume 45 is defined around the dwell positions. The relevant tissue property or properties are determined for all voxels within the subvolume, and an index value is calculated by accumulating the tissue property values for these voxels. The process can be made more efficient by considering multiple adjacent dwell positions together, i.e., defining a subvolume covering multiple dwell positions, and / or by caching a portion of the heterogeneity index for each subvolume. In this case, the total index value Given by Equation 3:
[0043] (3)
[0044] That is, the index value is given as the difference between the tissue density and the water density of the voxel over all voxels in the subvolume 45 divided by the voxel The distance from the center of the stop point For equation (1), some other material property, relative difference, or difference in a range of material properties may be considered instead of density. Furthermore, another uniform density may be used instead of the density of water. For methods involving ray tracing, a comparison between tissue properties of different voxels within the volume of interest can be used as an indicator of heterogeneity instead of or in addition to the comparison with water.
[0045] Therefore, the selection in step S23 can be decomposed as follows: Figure 5 The illustrated sub-steps: In a first step S51, using ray tracing and equations 1 and 2, or using a sub-volume and equation 3, an index value of a dwell position or a set of dwell positions is calculated. In step S52, the index value Compare with the threshold. If the index value is below the threshold, indicating that the tissue properties are similar to those of water and / or are relatively uniform, which means that a fast calculation algorithm can be used for the dwell position or location of interest, although the algorithm is less accurate. Above a threshold, this indicates that the tissue properties are different from those of water and / or are non-homogeneous, which means that a more accurate but more time-consuming calculation algorithm should be used for the dwell position or position of interest. It will be appreciated that for each position, there may be several different algorithms and thresholds, so that below a minimum threshold a very fast algorithm may be used, between the minimum threshold and a higher threshold an intermediate algorithm may be used, and above a higher threshold a slower but very accurate algorithm can be used.
[0046] In the simplest case, two calculation algorithms are used, an accurate but slow algorithm for where accuracy is needed and a faster but less accurate algorithm for less important voxels. For the accurate calculation algorithm, a dose engine such as a Monte Carlo dose engine or a Boltzmann equation solver can be used. For the fast but less accurate calculation algorithm, the analytical TG43 dose engine is most commonly used, as mentioned before. Algorithms using accurate and less accurate dose engines can be combined depending on their characteristics and the required dose calculation speed. Examples of dose calculation algorithms that can be used include:
[0047] Monte Carlo (MC). This algorithm is very accurate but is generally slower than other algorithms. The time varies with the size of the volume in which the dose is to be calculated and the number of approximations made within the MC engine. The time varies inversely with the expected statistical uncertainty.
[0048] Boltzmann equation solver. Speed and accuracy comparable to Monte Carlo.
[0049] Collapsed Cone (CC). Moderately fast. Capable of accounting for tissue heterogeneity, but includes approximations that make the algorithm less accurate under certain conditions, such as high heterogeneity, high energy, or large treatment volumes.
[0050] Pencil beam. Fast, but less accurate in non-uniform conditions.
[0051] SVD. Faster than pencil beam and CC. Comparable to pencil beam in accuracy.
[0052] Ray tracing. Very fast, but limited accuracy in non-uniform conditions.
[0053] TG43, currently the most commonly used. This algorithm is very fast, but tends to be inaccurate in conditions that are not uniform or similar to water.
[0054] For each algorithm listed, different settings can be used which will affect performance and accuracy.The combination of different algorithms as described above may also include using algorithms executed by the same dose engine but with different settings.
Claims
1. A computer-implemented dose calculation method for brachytherapy treatment, wherein: Radiation is provided by one or more radiation sources from at least a first dwell position and a second dwell position in a patient, the radiation provided at each dwell position producing a dose contribution from that dwell position, the method comprising selecting a first dose calculation algorithm to be used to calculate the dose contribution from the first dwell position and a second dose calculation algorithm to be used to calculate the dose contribution from the second dwell position, the second dose calculation algorithm being different from the first dose calculation algorithm, calculating the dose contribution from the first dwell position according to the first dose calculation algorithm and calculating the dose contribution from the second dwell position according to the second dose calculation algorithm, and calculating a total dose as the sum of the dose contributions from the at least first dwell position and the second dwell position.
2. The dose calculation method according to claim 1, wherein: The first dose calculation algorithm is an analytical method that assumes a uniform density of tissue surrounding the first dwell position, such as the density of water.
3. The dosage calculation method according to claim 1 or 2, wherein: The second dose calculation algorithm is arranged to take into account heterogeneity in tissue surrounding the second dwell position.
4. A method according to any one of the preceding claims, wherein: The dose calculation algorithm for each dwell position is selected based on the geometry of the surroundings of the dwell position and / or the geometry of the radiation source.
5. A dose calculation method according to any one of the preceding claims, wherein: The dose calculation algorithm to be used for each dwell position is selected based on an index value indicating a difference in material properties such as density between water and the tissue surrounding the dwell position, or an index value of a change in material properties in the tissue surrounding the dwell position, or a combination of both.
6. The method according to claim 5, wherein: The index value for each dwell location is based on a heterogeneity index for the dwell location, the heterogeneity index indicating variations in tissue properties in a volume surrounding the dwell location.
7. The method according to claim 6, wherein: The heterogeneity index for each dwell position is calculated based on ray tracing in two or more directions about the dwell position and determining the tissue properties of intersecting voxels for each ray tracing operation.
8. The method according to claim 6, wherein: The heterogeneity index for each dwell position is calculated based on defining sub-volumes around each dwell position, each sub-volume comprising a plurality of voxels and determining the tissue characteristics in at least some of the plurality of voxels.
9. A method according to any one of the preceding claims, wherein: The dose calculation algorithm for each dwell location is selected based on a comparison of material properties of tissue surrounding the dwell location with a homogeneous reference material.
10. The method according to any one of the preceding claims, further comprising performing a third dose calculation for a third dwell position according to a third dose calculation algorithm, and using the sum of the first dose calculation, the second dose calculation and the third dose calculation as a total calculated dose.
11. A computer-implemented brachytherapy optimization method for optimizing a set of dwell times for a corresponding set of dwell positions, the optimization method comprising calculating a total dose using the method according to any one of the preceding claims and using the calculated total dose in the optimization process.
12. A computer program product arranged to perform a dose calculation according to a first dose calculation algorithm and a second dose calculation algorithm, the computer program product comprising computer readable code means which, when executed in a computing device, will cause the computing device to perform a method according to any one of the preceding claims.
13. A computer program product comprising a non-transitory storage medium having stored thereon the computer program product according to claim 12.
14. A computer comprising a processor and a program memory having a computer program product according to claim 12 stored therein such that the computer program product can be executed by the processor.