CN110170109B - Orthogonal double-layer grating device for radiotherapy equipment and subfield segmentation control method thereof - Google Patents

Orthogonal double-layer grating device for radiotherapy equipment and subfield segmentation control method thereof Download PDF

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CN110170109B
CN110170109B CN201811577792.3A CN201811577792A CN110170109B CN 110170109 B CN110170109 B CN 110170109B CN 201811577792 A CN201811577792 A CN 201811577792A CN 110170109 B CN110170109 B CN 110170109B
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blade
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CN110170109A (en
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文虎儿
关睿雪
姚毅
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Suzhou Linatech Medical Science And Technology Co ltd
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    • A61N5/00—Radiation therapy
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    • A61N5/1031—Treatment planning systems using a specific method of dose optimization
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61N—ELECTROTHERAPY; MAGNETOTHERAPY; RADIATION THERAPY; ULTRASOUND THERAPY
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    • A61N5/1042—X-ray therapy; Gamma-ray therapy; Particle-irradiation therapy with spatial modulation of the radiation beam within the treatment head
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    • A61N5/1045—X-ray therapy; Gamma-ray therapy; Particle-irradiation therapy with spatial modulation of the radiation beam within the treatment head using a multi-leaf collimator, e.g. for intensity modulated radiation therapy or IMRT
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Abstract

The invention provides an orthogonal double-layer grating device for radiotherapy equipment and a subfield segmentation control method thereof. Wherein the double-deck grating device of quadrature installs under radiotherapy equipment's accelerator aircraft nose, includes: the plane of the upper grating blade and the plane of the lower grating blade are parallel to each other and perpendicular to the direction of a ray emitted by the accelerator head, and the moving directions of the upper grating blade and the lower grating blade are orthogonal; the subfield segmentation control method is based on the alternating double-layer grating device. The orthogonal double-layer grating device for radiotherapy equipment and the subfield segmentation control method thereof provided by the invention can obviously improve the conformality and the treatment efficiency, and have extremely important significance for clinic.

Description

Orthogonal double-layer grating device for radiotherapy equipment and subfield segmentation control method thereof
Technical Field
The invention relates to the field of radiotherapy equipment, in particular to an orthogonal double-layer grating device for radiotherapy equipment and a subfield segmentation control method thereof.
Background
Radiation therapy, as a local treatment for tumors, is continuously seeking to solve a fundamental problem of how to better deal with the dose relationship between tumor tissue (target volume) and surrounding normal tissue, so that the tumor is locally controlled to the maximum extent and the radiation damage to the surrounding normal tissue and organs is minimized.
The grating is a multi-leaf collimator which is essential for modern radiotherapy equipment, and can have a very good conformal effect on a target area through the movement of the grating leaves, in general, the thinner the leaves of the multi-leaf collimator are, the more the number of the leaves is, the better the conformality of the multi-leaf collimator is, but for a conventional single-layer grating, as the leaves can only move in one direction, the conformality in the thickness direction of the leaves is limited, and for a parallel double-layer grating, although the conformality in the thickness direction of the leaves is improved compared with that of the single-layer grating, the thickness of the leaves is limited by the influence of the leaf thickness, and the leaves cannot move or form an irradiation unit at any position; for example, the chinese patent with application No. 201520205602.0 discloses a grating device for radiotherapy equipment, wherein a tail position controller and a front position controller are simultaneously arranged to simultaneously check the tail position and the middle position of a single grating blade, and to measure the time and/or the total number of revolutions of a motor when a certain grating blade reaches the middle position from the tail position, because the distance between the tail position and the middle position is determined and not changed and can be accurately measured, it accurately verifies and controls a certain grating blade to reach a certain accurately specified position, because it can conveniently realize the one-by-one check and control of the grating blade, it can effectively overcome the transmission error and the unstable performance error caused by different grating blade driving systems, and it achieves better conformal effect by realizing the accurate displacement of each grating blade, but the essential principle that the grating carries out conformal shielding is not changed, the irradiation efficiency is still low, grating leakage exists, organs at risk cannot be better protected, and the improvement is urgently needed.
A step-shot method for dividing static intensity-modulated sub-fields is characterized in that a sub-field sequence is divided, the intensity distribution required by a plan is layered, then single-layer grating motion is controlled, each field is divided into a series of sub-fields to be irradiated once until all the sub-fields are irradiated, and the intensity distribution required by the plan is realized, and the step-shot method comprises the following steps:
firstly, a Treatment Planning System (TPS) calculates an intensity matrix after optimization of each field according to dose constraint or biological constraint of organs and a target region and an optimization engine, and the intensity matrix is marked as P[p×q]Where p, q are the number of samples of the matrix;
next, for subfield segmentation, the optimized matrix is resampled here in the thickness direction of the leaf. If the grating is horizontally installed, the matrix after resampling is marked as D[M×N]M is the number of blades in the intensity map, N is 256, the sampling interval of the matrix in the vertical direction is the thickness of the blades, and the sampling interval in the horizontal direction is 0.25; the large sampling interval in the vertical direction of the resample matrix compared with the original matrix means that the strength matrix of the process is lost in the practical situation that the conformal capability of the blade in the thickness direction of the blade is poor.
Dividing the intensity distribution in the previous step into step-shaped intensity levels according to equal intensity intervals, wherein the intensity level size determines the segmentation precision and the subfield complexity; in general, 10 levels are divided, and the matrix after division is marked as A[M×N]；
Finally, the subfield segmentation is started, the intensity matrix A[M×N]Can be divided into a plurality of sub-fields:
Figure GDA0002732321750000021
wherein u iskIs the MU value, SkIs a sub-field matrix; the total MU value and the total number of sub-fields determine the irradiation efficiency, and the lower the total MU value, the smaller the total number of sub-fields, and the shorter the irradiation time, the higher the efficiency. At this time, one third of the current maximum intensity is selected as a segmentation intensity value, a matrix (a subfield matrix) segmented this time is selected under the condition of the segmentation intensity value, and the segmentation matrix is subtracted from the current intensity matrix:
A＝A-ukSk (2)
repeatedly selecting the segmentation intensity value and the segmentation matrix until A[M×N]And reduced to 0.
When selecting the sub-field matrix, the sub-field S is noticedkIs formed by a plurality of pairs of leaf (MLC) apertures, where there are defined m pairs of leaves in the intensity map, and the positions of the left and right leaves (for example a 0 ° single layer grating) of each pair of leaves are l, r, respectively, then the leaf spacing I is:
I＝{x∈[n]：l≤x≤r} (3)
the subdomains can be represented as:
Figure GDA0002732321750000031
for each pair of blades, the section with the largest blade interval is taken as an opening, namely the length of the blade interval I is the largest. For example, (1, 1, 1, 0, 1, 0), the single layer grating will take (1, 1, 1, 0, 0, 0) as its aperture shape for the first time, and will be divided in two.
Under the condition that the blades are not overlapped, a constraint exists between the blade pairs, namely the blade non-overlapping constraint (inter-blade overlapping constraint-ICC), namely an overlapping area alpha exists in FIG. 1, so that two conditions cannot occur in FIG. 1, and for a single-layer grating (parallel single-layer grating), in order to meet the condition that the blades are not overlapped, the two conditions can be completed by dividing twice. Thus, the multi-segment intensity profile and the non-blade-overlap constraint both limit the illumination efficiency of a single layer grating.
Specifically, taking the sub-field segmentation of a 5 × 8 matrix containing multiple connected regions of the following "tian" -shaped intensity map as an example (where 1 or 2 in the matrix represents normal tissue for the target region and its dose intensity, then 0 is used), in order to achieve the constraint of multi-segment intensity distribution map and non-overlapping of the leaves, a single-layer raster segmentation of 0 ° installation divides the intensity matrix into the following four segmentations:
Figure GDA0002732321750000032
according to the above-mentioned division method, the division result of the 0 ° single-layer grating to the "field" shaped intensity map is shown in fig. 6, and the grating blade positions in fig. 6 correspond to the matrix four times division respectively, and correspond to the matrix four times division sequentially; the result of the same 90 ° installation of a single layer grating on a field-shaped intensity map is shown in fig. 7.
Obtaining an optimized intensity matrix (P) according to the optimized radiation field[p×q]) The method of (1) and the subfield dividing method described above, the result of dividing the intensity map of the shape of the Chinese character "pin" by the single layer grating mounted at 0 ° is shown in fig. 9; the result of dividing the strength graph of the delta-shaped structure by the single-layer grating mounted at 90 ° is shown in fig. 10, and is not described herein.
In summary, both single layer grating and parallel double layer grating have the following problems;
1, the conformality in the thickness direction of the blade is not enough;
2, in order to satisfy the condition that the irradiation efficiency of the single-layer grating is limited by the multi-section intensity distribution diagram and the non-overlapping constraint of the blades, a complex field can be formed only by a plurality of sub-fields, and the irradiation efficiency is low.
Disclosure of Invention
In order to solve the above problems, the present invention provides an orthogonal double-layer grating device for radiotherapy equipment and a subfield segmentation control method thereof. The orthogonal double-layer grating device for radiotherapy equipment and the subfield segmentation control method thereof provided by the invention can obviously improve the conformality and the treatment efficiency, and have extremely important significance for clinic.
The technical scheme of the invention is as follows: an orthogonal double-layer grating device for radiotherapy equipment is arranged below an accelerator handpiece of the radiotherapy equipment and comprises:
the plane of the upper grating blade and the plane of the lower grating blade are parallel to each other and perpendicular to the direction of a ray emitted by the accelerator head, and the moving directions of the upper grating blade and the lower grating blade are orthogonal;
the upper layer grating blade comprises a left blade and a right blade and is used for searching and moving towards the left side and the right side of the target area;
the lower grating blade comprises an upper blade and a lower blade and is used for searching and moving towards the upper side and the lower side of the target area;
and the controller is used for driving each sub-blade of the left blade, the right blade, the upper blade and the lower blade to move independently so as to achieve the purpose of conforming to the target area.
A step-shot control method using the above orthogonal double-layer grating device for radiotherapy apparatus, comprising the steps of:
s1: determining an optimization matrix of dose intensities determined by a Treatment Planning System (TPS);
s2: resampling the optimization matrix in the step S1, and adjusting the dimension of the optimization matrix;
s3: dividing the matrix re-sampled in the step S2 into step-shaped intensity levels at equal intervals according to intensity;
s4: determining a segmentation strength value according to the maximum strength in the step S3, and solving a matrix of the current segmentation under the segmentation strength value;
s5: and calculating the maximum rectangular range of the contour of the segmentation matrix, calculating the intensity matrix range of the grating blade needing conformal according to the maximum rectangular range, and moving the left blade and the right blade, and the upper blade and the lower blade to conform to the edge of the intensity matrix range.
In a preferred embodiment of the present invention, based on the above, the optimization matrix in step S1 is denoted as P[p×q]Adjusting P in said step S2[p×q]The values of p and q in (1) and are marked as D[M×N]M is set to 256, N is set to 256, and the sampling interval of the matrix in the vertical direction and the horizontal direction is set to 0.25;
the step intensity level divided at equal intervals of intensity in the step S3 is 10 levels, and the intensity value divided in the step S4 is one third of the current maximum intensity.
Further, in step S5, the method for moving the left and right blades, the upper and lower blades to conform to the edge of the intensity matrix range is: searching the left blade from left to right until the target area is hit, and searching the corresponding right blade from right to left until the target area is hit; if the left leaflet fails to hit the target area, the set of leaflets is closed at the edge; searching the upper leaves from top to bottom until the target area is hit, and searching the corresponding lower leaves from bottom to top until the target area is hit; if the upper lobe fails to hit the target area, the set of lobes is closed at the edge.
Further, the method also comprises the step of shielding the leakage point:
s6: after the upper leaflet, the lower leaflet, the left leaflet and the right leaflet perform conformal movement in the step S5, calculating an actual segmentation matrix, and comparing the actual segmentation matrix with the optimized matrix of the dose intensity determined in the step S1, that is, a desired matrix; if the actual partition matrix is larger than the expected partition matrix, the position of the blade is adjusted, and pixel points, namely missed-shot points, at the positions where the actual partition matrix is larger than the expected partition matrix are shielded and are smaller than or equal to the expected partition matrix.
Further, the method for shielding the leakage point in step S6 includes the following steps:
t1: searching pixel points of which the actual partition matrix is larger than the expected partition matrix, and creating a matrix for storing abnormal points;
t2: scanning all the points of the abnormal matrix in the step T1 line by line, calculating the effective distances between the current abnormal point and the blades corresponding to the upper, lower, left and right directions, wherein the distances represent the number of points of the normal point to be covered when the blade is shielded to the current abnormal point, and the blade corresponding to the upper blade, the lower blade, the left blade and the right blade in the four directions with the minimum effective distance is selected as a shielding blade, and the current blade position is updated;
t3: and after scanning of all the points of the abnormal matrix is finished, comparing the current blade position in the step T2 with the expected segmentation matrix, updating the abnormal matrix, judging whether abnormal points exist or not, and if so, repeating the steps T1-T2.
Further, in the step T1, the method for finding the outlier includes: for the horizontally installed grating, if the center position of a certain pixel point of the matrix falls between the upper edge and the lower edge of a certain blade of the grating, the pixel point is considered to be subordinate to the blade; for the vertically installed grating, if the center position of a certain pixel point of the matrix falls between the left edge and the right edge of a certain blade of the grating, the pixel point is considered to be subordinate to the blade; if the state (open or closed) of the blade at the pixel point is consistent with the state (0 or 1) of the expected matrix, the pixel point is considered to be normal, otherwise, the pixel point is considered to be abnormal.
As a preferred embodiment of the present invention, based on the above, the method further comprises the step of optimizing the segmentation:
s7: subtracting the actual segmentation matrix adjusted in the step S6 from the total segmentation matrix to obtain a new segmentation matrix, and repeating the steps S4-S5 until the new segmentation matrix is 0;
s8: and (3) optimizing all the sub-fields in the step by adopting a least square method to ensure that the final segmentation result is the minimum with the expected matrix in the step 1, and completing the segmentation.
As another preferred embodiment of the present invention, based on the above, the method further comprises the step of adjusting the segmentation strength value to reduce the total MU:
s7: calculating the area of the actual segmentation matrix in the step S6, and taking the product of the area and the segmentation strength value as an evaluation criterion; if the product value after the current segmentation is finished is larger than the product value of the last segmentation, subtracting one from the segmentation strength value in the step S4, solving a matrix of the current segmentation, and repeating the steps S5-S6; otherwise, go to step S8;
s8: subtracting the actual segmentation matrix in the step S6 from the total segmentation matrix to obtain a new segmentation matrix, and repeating the steps S4-S7 until the new segmentation matrix is 0;
s9: and (3) optimizing all the sub-fields in the step by adopting a least square method to ensure that the final segmentation result is the minimum with the expected matrix in the step 1, and completing the segmentation.
The invention has the beneficial effects that:
1) the method comprises the steps of firstly utilizing the blades around the orthogonal double-layer grating to synchronously conform to the position of a target area (the edge of an intensity matrix), and then detecting whether the inside of one or more enclosed areas has a missed emission point or not. The single-layer tube grating overcomes the defect that the irradiation efficiency is limited in order to meet the requirements of a multi-section intensity distribution diagram and the non-overlapping constraint of blades in the conventional single-layer tube grating.
2) The orthogonal double-layer grating has the advantage of conformality, and the double-layer grating can effectively reduce grating leakage and better protect organs at risk.
3) The sub-field segmentation control method based on the orthogonal double-layer grating device solves the problems that a complex radiation field can be formed only by a plurality of sub-fields, and the irradiation efficiency is low.
In conclusion, the orthogonal double-layer grating device for radiotherapy equipment and the subfield segmentation control method thereof provided by the invention can obviously improve the conformality and the treatment efficiency, and have extremely important significance for clinic.
Drawings
FIG. 1 is a schematic view of a single layer grating subfield segmented leaf overlap;
FIG. 2 is a schematic diagram of an orthogonal double layer grating to account for blade overlap;
FIG. 3 is an overall flow chart of the orthogonal double-layer grating subfield division according to the present invention;
FIG. 4 is a flow chart of the orthogonal double grating blade shading of the present invention;
FIG. 5 is a flow chart of a method for reducing total MU by orthogonal double layer grating according to the present invention;
FIG. 6 is a segmentation of a 0 ° installed single layer grating versus a "field" shaped intensity plot;
FIG. 7 is a segmentation of a 90 degree installation of a single layer grating against a field strength map;
FIG. 8 is a graph of the intensity of the orthogonal double layer grating of the present invention;
FIG. 9 is a segmentation result of a 0-degree mounted single layer grating versus a "pin" shaped intensity map;
FIG. 10 is a segmentation result of a 90-degree mounted single layer grating versus a "pin" shaped intensity plot;
FIG. 11 is a result of the segmentation of the "PIN" -shaped intensity map by the orthogonal double-layer grating according to the present invention;
figure 12 is a DVH plot of prostate 1 (bands are orthogonal bilayer grating results);
fig. 13 is a DVH plot of brain metastasis multi-target volume (bands are orthogonal bilayer grating results);
fig. 14 is a DVH plot of prostate 2 (bands are orthogonal bilayer grating results);
figure 15 is a DVH plot (bands are orthogonal bilayer grating results) of rectal cancer;
FIG. 16 is a DVH plot (bands are orthogonal bilayer grating results) of liver cancer;
figure 17 is a DVH plot of lower esophageal cancer (bands are orthogonal bilayer grating results);
figure 18 is a DVH plot (bands are orthogonal bilayer grating results) of pancreatic cancer;
figure 19 is a DVH plot (bands are orthogonal bilayer grating results) of cervical cancer;
fig. 20 is a DVH plot (bands are orthogonal bilayer grating results) of gastric cancer;
fig. 21 is a DVH plot (bands are orthogonal double layer grating results) of peripheral lung cancer;
FIG. 22 is a DVH plot of celiac lymph node metastasis (bands are orthogonal double layer grating results);
figure 23 is a DVH plot (bands are orthogonal double layer grating results) for breast cancer;
FIG. 24 is a chart of subfield segmentation statistics comparing the double-layer grating and the single-layer grating of the present invention in 12 cases of FIGS. 12-23;
FIG. 25 is a graph of a comparison of the segmentation statistics of a modified double layer grating, a modified pre-double layer grating, and a single layer grating.
Detailed Description
The technical solution of the present invention will be clearly and completely described below.
An orthogonal double-layer grating device for radiotherapy equipment is arranged below an accelerator handpiece of the radiotherapy equipment, as shown in fig. 2, and comprises:
the plane of the upper grating blade and the plane of the lower grating blade are parallel to each other and perpendicular to the direction of a ray emitted by the accelerator head, and the moving directions of the upper grating blade and the lower grating blade are orthogonal; it should be noted that the upper and lower layers are relative to the vertical height of the orthogonal double-layer grating device.
The upper layer grating blade comprises a left blade 1 and a right blade 2 and is used for searching and moving towards the left side and the right side of the target area;
the lower grating blade comprises an upper blade 3 and a lower blade 4, and is used for searching and moving towards the upper side and the lower side of the target area; it should be noted that the upper and lower blades are in terms of the front and rear positions relative to the lower grating blade, or target plane. The above orientations are used to illustrate the position and displacement relationship of the grating blades of the present invention, and are not to be construed as limiting the present invention.
And the controller is used for driving each sub-blade of the left blade, the right blade, the upper blade and the lower blade to move independently so as to achieve the purpose of conforming to the target area. By adopting the grating blades which are parallel and orthogonal in walking position, the target area has higher conformality, and the walking precision of less than 1mm can be achieved in two directions.
A subfield segmentation control method, which uses the above orthogonal double-layer grating device for radiotherapy equipment, as shown in fig. 3, includes the following steps:
s1: determining an optimization matrix of dose intensities determined by a Treatment Planning System (TPS); the optimization matrix is obtained by optimizing and calculating the TPS system according to the dose constraints and other constraints of the target area and the organs at risk, the final dose distribution of the target area and the organs at risk is determined by the optimization matrix, the closer the actual matrix after the subfield segmentation is to the optimization matrix, the closer the actual dose distribution is to the optimized dose distribution, and the higher the quality of the generated treatment plan is;
s2: resampling the optimization matrix in the step S1, and adjusting the dimension of the optimization matrix; when the traditional single-layer grating is used for resampling, the sampling interval of the motion direction of the blade is related to the walking precision of the actual blade, and is generally smaller; the sampling interval in the thickness direction of the blade is directly divided according to the thickness of the blade, the process is a down-sampling process, and the strength matrix has loss. When the orthogonal double-layer grating is used for resampling, the blades in two directions are considered to move, so that the sampling intervals of the intensity matrix in the two orthogonal directions are kept consistent, the sampling intervals are related to the displacement accuracy of the actual blades, and the sampling intervals are generally smaller than the thickness of the blades. When the orthogonal grating intensity matrix is resampled, the loss is smaller compared with the original matrix.
S3: dividing the matrix re-sampled in the step S2 into step-shaped intensity levels at equal intervals according to intensity; the magnitude of the intensity level determines the accuracy of the segmentation, and the complexity of the segments. The higher the intensity level, the smaller the error between the divided matrix and the original matrix, but at the same time, the number of subfields increases, and the irradiation time becomes longer.
S4: determining a segmentation strength value according to the maximum strength in the step S3, and solving a matrix of the current segmentation under the segmentation strength value;
s5: and calculating the maximum rectangular range of the contour of the segmentation matrix, calculating the intensity matrix range of the grating blade needing conformal according to the maximum rectangular range, and moving the left blade and the right blade, and the upper blade and the lower blade to conform to the edge of the intensity matrix range.
In a preferred embodiment of the present invention, based on the above, the optimization matrix in step S1 is denoted as P[p×q]Adjusting P in said step S2[p×q]The values of p and q in (1) and are marked as D[M×N]M is set to 256, N is set to 256, and the sampling interval of the matrix in the vertical direction and the horizontal direction is set to 0.25;
the step intensity level divided at equal intervals of intensity in the step S3 is 10 levels, and the intensity value divided in the step S4 is one third of the current maximum intensity. The technical parameters are adopted, and the orthogonal double-layer grating is practically applicable to the orthogonal double-layer grating.
Further, in step S5, the method for moving the left and right blades, the upper and lower blades to conform to the edge of the intensity matrix range is: searching the left blade from left to right until the target area is hit, and searching the corresponding right blade from right to left until the target area is hit; if the left leaflet fails to hit the target area, the set of leaflets is closed at the edge; searching the upper leaves from top to bottom until the target area is hit, and searching the corresponding lower leaves from bottom to top until the target area is hit; if the upper lobe fails to hit the target area, the set of lobes is closed at the edge.
Further, the method also comprises the step of shielding the leakage point:
s6: after the upper leaflet, the lower leaflet, the left leaflet and the right leaflet perform conformal movement in the step S5, calculating an actual segmentation matrix, and comparing the actual segmentation matrix with the optimized matrix of the dose intensity determined in the step S1, that is, a desired matrix; if the actual partition matrix is larger than the expected partition matrix, the position of the blade is adjusted, and pixel points, namely missed-shot points, at the positions where the actual partition matrix is larger than the expected partition matrix are shielded and are smaller than or equal to the expected partition matrix.
Further, as shown in fig. 4, the method for shielding the leakage point in step S6 includes the following steps:
t1: searching pixel points, namely missing points or abnormal points, of which the actual partition matrix is larger than the expected partition matrix, and creating a matrix for storing the abnormal points;
t2: scanning all the points of the abnormal matrix in the step T1 line by line, calculating the effective distances between the current abnormal point and the blades corresponding to the upper, lower, left and right directions, wherein the distances represent the number of points of the normal point to be covered when the blade is shielded to the current abnormal point, and the blade corresponding to the upper blade, the lower blade, the left blade and the right blade in the four directions with the minimum effective distance is selected as a shielding blade, and the current blade position is updated;
t3: and after scanning of all the points of the abnormal matrix is finished, comparing the current blade position in the step T2 with the expected segmentation matrix, updating the abnormal matrix, judging whether abnormal points exist or not, and if so, repeating the steps T1-T2.
Further, in the step T1, the method for finding the outlier includes: for the horizontally installed grating, if the center position of a certain pixel point of the matrix falls between the upper edge and the lower edge of a certain blade of the grating, the pixel point is considered to be subordinate to the blade; for the vertically installed grating, if the center position of a certain pixel point of the matrix falls between the left edge and the right edge of a certain blade of the grating, the pixel point is considered to be subordinate to the blade; if the state (open or closed) of the blade at the pixel point is consistent with the state (0 or 1) of the expected matrix, the pixel point is considered to be normal, otherwise, the pixel point is considered to be abnormal.
As a preferred embodiment of the present invention, based on the above, it is different that, as shown in fig. 3, the method further includes a step of optimizing the segmentation (referred to as a modified pre-bilayer grating):
s7: subtracting the actual segmentation matrix adjusted in the step S6 from the total segmentation matrix to obtain a new segmentation matrix, and repeating the steps S4-S5 until the new segmentation matrix is 0;
s8: and (3) optimizing all the sub-fields in the step by adopting a least square method to ensure that the final segmentation result is the minimum with the expected matrix in the step 1, and completing the segmentation.
Based on the orthogonal double-layer grating device for radiotherapy equipment and the subfield segmentation control method thereof, the intensity matrix is divided into two parts by taking the subfield segmentation of a 5 multiplied by 8 matrix (C) containing a plurality of connected regions of the following field-shaped intensity map as an example: taking one third of the maximum intensity value as a segmentation intensity value for the first time, taking 1 as an intensity segmentation value in the example, closing the surrounding leaves to the edge of the intensity graph, and checking whether abnormal points exist in the interior, wherein the abnormal points do not exist in the example, so that the leaf shielding program is not required to be executed, and the segmentation is finished for the first time to obtain a residual intensity matrix; and (5) performing the same segmentation processing on the residual intensity matrix for the second time to finish the second segmentation, wherein the residual intensity matrix minus the second segmentation matrix is the second residual matrix, the matrix is divided into C1+ C2, the internal values of the matrix at the moment are all 0, and the segmentation is finished. The segmentation results were as follows:
Figure GDA0002732321750000131
in this case, the parallel single layer grating needs to be divided into two divisions, but as shown above, the orthogonal double layer grating can be divided into one division. Especially, the intensity matrix containing a plurality of isolated areas is adopted, the orthogonal double-layer grating can be segmented at one time, and the non-overlapping constraint (interlace alignment-ICC) of the single-layer grating is eliminated, so that the irradiation efficiency is greatly improved.
The program operation result on TPS in this example is shown in fig. 8, and it can be seen that in this example, the total MU and the number of sub-fields of the sub-field segmentation of the orthogonal double-layer grating are reduced compared to the single-layer grating. Continuing with the example of the "pin" shaped intensity matrix, the contrast graphs of the single-layer grating and the double-layer grating are shown in fig. 9-11, which shows that for some intensity graphs containing multiple connected regions, the number of divided sub-fields of the orthogonal double-layer grating is small, the total MU is low, and the irradiation efficiency is high. Meanwhile, the single-layer grating has a blade gap limitation (the minimum gap between the left blade and the right blade of a pair of blades), so that a narrow gap exists between each pair of blades outside the intensity matrix, and radiation leakage is caused. And two layers of gratings of the double-layer grating can play a complementary role, the vertically-installed grating can shield the narrow gap of the horizontal grating, and the horizontal grating can also shield the narrow gap of the vertically-installed grating, so that the double-layer grating has less radiation leakage. In addition, the transmission of radiation through a double layer grating is also reduced compared to a single layer grating. In conclusion, the double-layer grating can reduce the transmission and the leakage of rays and better protect organs at risk.
Next, an algorithm for the occlusion of the leaf in step S6 will be described by taking a 4 × 4 intensity matrix as an example. It is first assumed herein that the mounting thickness for horizontally mounted gratings and vertically mounted gratings is consistent with the intensity matrix sampling interval (i.e., a pair of blades may occlude a row or column of data). Then for the initial optimization matrix A below, the surrounding leaves are first conformed to the matrix edges to form the actual segmentation matrix A1It can be seen that the actual segmentation matrix is larger than the initial optimization matrix, and an abnormal point "0" exists inside the actual segmentation matrix.
Figure GDA0002732321750000141
The blade shielding algorithm is implemented below, the position of the '0' is subject to the second pair of horizontal blades (from top to bottom), the second pair of vertical blades (from right to left), if the left blade is to shield the '0', 2 effective values need to be shielded, the effective distance is 2, the effective distance of the right blade in the same way is 1, the effective distance of the upper blade is 1, and the effective distance of the lower blade is 2, therefore, the upper blade or the right blade can be selected as the shielding blade. If the upper leaf is selected as the shielding leaf, the actual partition matrix is formed as A2Once the segmentation is complete, the second segmentation may continue. Eventually resulting in a segmentation result as shown in fig. 8. By using the above method, the result of dividing the "pin" shaped intensity map by the orthogonal double-layer grating is finally shown in fig. 11, which is not described herein again.
The premise of the above example is that the thickness of the horizontal and vertical leaves is consistent with the sampling interval of the matrix, assuming there is no consistency, the horizontal leaf thickness is twice the sampling interval of the matrix, while the vertical leaf thickness is still equal to the sampling interval, then the surrounding leaves conform to the edges of the matrix, forming the actual segmentation matrix as B1Two missed spots are visible. Firstly, analyzing the leakage points of the second row and the third column, wherein the leakage points belong to the first pair of horizontal blades and the second pair of vertical blades, if the leakage points are shielded, the left blade shields 5 effective points, the effective distance is 5, the effective distance of the right blade is 2, and the upper blade is effectiveThe distance is 1, the effective distance of the lower blade is 2, and therefore the upper blade is selected for shielding. Then, the leakage point of the third row and the second column is analyzed, the leakage point belongs to the second pair of horizontal blades and the third pair of vertical blades, the effective distance of the left blade is 1, the effective distance of the right blade is 3, the effective distance of the upper blade is 2, the effective distance of the lower blade is 1, and the lower blade is selected as a shielding blade. The division matrix finally formed is B2And after the current segmentation is finished, continuing to perform next segmentation.
Figure GDA0002732321750000151
As another preferred embodiment of the present invention, based on the above, it is different from that, as shown in fig. 5, the method further includes the step of adjusting the segmentation strength value to reduce the total MU (modified double-layer grating):
s7: calculating the area of the actual segmentation matrix in step S6, and taking the product of the area and the segmentation strength value as an evaluation criterion (called benefit); if the product value (benefit) after the current segmentation is finished is larger than the product value (benefit) of the last segmentation, subtracting one from the segmentation strength value in the step S4, solving the matrix of the current segmentation, repeating the steps S5-S6, and performing segmentation again; otherwise, go to step S8;
s8: subtracting the actual segmentation matrix in the step S6 from the total segmentation matrix to obtain a new segmentation matrix, and repeating the steps S4-S7 until the new segmentation matrix is 0;
s9: and (3) optimizing all the sub-fields in the step by adopting a least square method to ensure that the final segmentation result is the minimum with the expected matrix in the step 1, and completing the segmentation.
By adopting the method for adjusting the segmentation intensity values and reducing the total MU in the embodiment, the segmentation intensity value of each segmentation is adjusted by taking the product of the segmented subfield area and the segmentation intensity value as an evaluation standard. The defects that in the later stage of subfield segmentation, due to the fact that the distribution of the inner points of the intensity matrix is irregular (a large number of concave polygons exist), a large number of effective points are shielded by double-layer grating blades, the segmentation times are increased, and the total MU value is high are overcome.
Based on the orthogonal double-layer grating device for radiotherapy equipment and the subfield segmentation control method thereof, the method is applied to actual cases shown in fig. 12-23, 12 different cases are selected for testing, the number of subfields and MU statistical results thereof are shown in fig. 24 and 25, it can be seen that the total MU value of 8 cases in 12 cases is reduced to different degrees, the multi-target-region cases such as the multi-target region of brain metastasis are most significant, the number of subfields is increased except for one case, and the number of cases is kept equal, and other cases are reduced to different degrees. Comparing the dose volume histogram-DVH plots (fig. 12-23) for 12 cases, it was shown that orthogonal bi-layer gratings can better protect organs at risk (with a bi-layer grating, with the DVH curve positioned lower). In conclusion, the orthogonal double-layer grating can reduce the total MU and the total number of sub-fields, improve the irradiation efficiency and better protect organs at risk.
It will be apparent to those skilled in the art that various changes and modifications can be made without departing from the inventive concept thereof, and these changes and modifications can be made without departing from the spirit and scope of the invention.

Claims (5)

1. A subfield segmentation control method uses an orthogonal double-layer grating device for radiotherapy equipment, and the orthogonal double-layer grating device for the radiotherapy equipment is arranged below an accelerator handpiece of the radiotherapy equipment, and comprises the following steps:
the plane of the upper grating blade and the plane of the lower grating blade are parallel to each other and perpendicular to the direction of a ray emitted by the accelerator head, and the moving directions of the upper grating blade and the lower grating blade are orthogonal;
the upper layer grating blade comprises a left blade and a right blade and is used for searching and moving towards the left side and the right side of the target area;
the lower grating blade comprises an upper blade and a lower blade and is used for searching and moving towards the upper side and the lower side of the target area;
the controller is used for driving each sub-blade of the left blade, the right blade, the upper blade and the lower blade to move independently so as to achieve the purpose of conforming to the target area;
it is characterized in that the preparation method is characterized in that,
the method comprises the following steps:
s1: determining an optimization matrix of dose intensities determined by a Treatment Planning System (TPS);
s2: resampling the optimization matrix in the step S1, and adjusting the dimension of the optimization matrix;
s3: dividing the matrix re-sampled in the step S2 into step-shaped intensity levels at equal intervals according to intensity;
s4: determining a segmentation strength value according to the maximum strength in the step S3, and solving a matrix of the current segmentation under the segmentation strength value;
s5: calculating the maximum rectangular range of the contour of the current segmentation matrix, calculating the intensity matrix range of the grating blade needing conformal shape according to the maximum rectangular range, and moving the left blade and the right blade, and the upper blade and the lower blade to conform to the edge of the intensity matrix range;
the optimization matrix in the step S1 is marked as P[p×q]Adjusting P in said step S2[p×q]The values of p and q in (1) and are marked as D[M×N]M is set to 256, N is set to 256, and the sampling interval of the matrix in the vertical direction and the horizontal direction is set to 0.25;
the step-shaped intensity level divided at equal intervals of intensity in the step S3 is 10 levels, and the divided intensity value in the step S4 is one third of the current maximum intensity;
in step S5, the method for moving the left and right blades, the upper and lower blades to conform to the edge of the intensity matrix range is: searching the left blade from left to right until the target area is hit, and searching the corresponding right blade from right to left until the target area is hit; if the left leaflet fails to hit the target area, the set of leaflets is closed at the edge; searching the upper leaves from top to bottom until the target area is hit, and searching the corresponding lower leaves from bottom to top until the target area is hit; if the upper leaf cannot hit the target area, the group of leaves is closed at the edge;
further comprising the step of blocking the missed shot point:
s6: after the upper leaflet, the lower leaflet, the left leaflet and the right leaflet perform conformal movement in the step S5, calculating an actual segmentation matrix, and comparing the actual segmentation matrix with the optimized matrix of the dose intensity determined in the step S1, that is, a desired matrix; if the actual partition matrix is larger than the expected partition matrix, the position of the blade is adjusted, and pixel points, namely missed-shot points, at the positions where the actual partition matrix is larger than the expected partition matrix are shielded and are smaller than or equal to the expected partition matrix.
2. The subfield segmentation control method according to claim 1, wherein the method of blocking the leakage point in the step S6 includes the steps of:
t1: searching pixel points of which the actual partition matrix is larger than the expected partition matrix, and creating a matrix for storing abnormal points;
t2: scanning all the points of the abnormal matrix in the step T1 line by line, calculating the effective distances between the current abnormal point and the blades corresponding to the upper, lower, left and right directions, wherein the distances represent the number of points of the normal point to be covered when the blade is shielded to the current abnormal point, and the blade corresponding to the upper blade, the lower blade, the left blade and the right blade in the four directions with the minimum effective distance is selected as a shielding blade, and the current blade position is updated;
t3: and after scanning of all the points of the abnormal matrix is finished, comparing the current blade position in the step T2 with the expected segmentation matrix, updating the abnormal matrix, judging whether abnormal points exist or not, and if so, repeating the steps T1-T2.
3. The subfield segmentation control method according to claim 2, wherein the method of searching for outliers in step T1 is: for the horizontally installed grating, if the center position of a certain pixel point of the matrix falls between the upper edge and the lower edge of a certain blade of the grating, the pixel point is considered to be subordinate to the blade; for the vertically installed grating, if the center position of a certain pixel point of the matrix falls between the left edge and the right edge of a certain blade of the grating, the pixel point is considered to be subordinate to the blade; if the state (open or closed) of the blade at the pixel point is consistent with the state (0 or 1) of the expected matrix, the pixel point is considered to be normal, otherwise, the pixel point is considered to be abnormal.
4. The subfield segmentation control method according to claim 1, characterized by the step of optimizing the segmentation:
s7: subtracting the actual segmentation matrix adjusted in the step S6 from the total segmentation matrix to obtain a new segmentation matrix, and repeating the steps S4-S5 until the new segmentation matrix is 0;
s8: and (3) optimizing all the sub-fields in the step by adopting a least square method to ensure that the final segmentation result is the minimum with the expected matrix in the step 1, and completing the segmentation.
5. The subfield segmentation control method according to claim 1, further comprising the step of adjusting the segmentation intensity value to reduce the total MU:
s7: calculating the area of the actual segmentation matrix in the step S6, and taking the product of the area and the segmentation strength value as an evaluation criterion; if the product value after the current segmentation is finished is larger than the product value of the last segmentation, subtracting one from the segmentation strength value in the step S4, solving a matrix of the current segmentation, and repeating the steps S5-S6; otherwise, go to step S8;
s8: subtracting the actual segmentation matrix in the step S6 from the total segmentation matrix to obtain a new segmentation matrix, and repeating the steps S4-S7 until the new segmentation matrix is 0;
s9: and (3) optimizing all the sub-fields in the step by adopting a least square method to ensure that the final segmentation result is the minimum with the expected matrix in the step 1, and completing the segmentation.
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