CN1202884C - Controlling delivery of radiotherapy - Google Patents
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- CN1202884C CN1202884C CNB998053899A CN99805389A CN1202884C CN 1202884 C CN1202884 C CN 1202884C CN B998053899 A CNB998053899 A CN B998053899A CN 99805389 A CN99805389 A CN 99805389A CN 1202884 C CN1202884 C CN 1202884C
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- A61N5/10—X-ray therapy; Gamma-ray therapy; Particle-irradiation therapy
- 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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- G21K1/00—Arrangements for handling particles or ionising radiation, e.g. focusing or moderating
- G21K1/02—Arrangements for handling particles or ionising radiation, e.g. focusing or moderating using diaphragms, collimators
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- G21K1/02—Arrangements for handling particles or ionising radiation, e.g. focusing or moderating using diaphragms, collimators
- G21K1/04—Arrangements for handling particles or ionising radiation, e.g. focusing or moderating using diaphragms, collimators using variable diaphragms, shutters, choppers
- G21K1/046—Arrangements for handling particles or ionising radiation, e.g. focusing or moderating using diaphragms, collimators using variable diaphragms, shutters, choppers varying the contour of the field, e.g. multileaf collimators
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- A—HUMAN NECESSITIES
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Abstract
An algorithm to generate discrete beam intensity modulation by dynamic multileaf collimation (MLC) is described which incorporates constraints on minimum allowed leaf separations. MLC positioning information is derived simultaneously for all leaf pairs and backup diaphragms as they progress across the field and a feedback mechanism allows corrections to be applied to eliminate potential violations of minimum separation conditions and any underexposure in the inter-leaf-tongue-and-groove region as they are encountered. The resulting motion correctly delivers the intended modulation and is physically realisable. Results of the algorithm can also alternatively be interpreted as defining a series of static fields to deliver the same modulation.
Description
Technical field
The present invention relates to a kind of linear accelerator, the radiation dose that it adopts the output of many thin slices collimator to change in whole area for treatment.
Background technology
How by dynamic many thin slice collimations (for example many authors have described the radiocurable intensity modulated of conformal field is, people (1998) such as K llman, Convery and Rosenbloom (1992), Spirou and Chui (1994), people such as Stein (1994), people such as Svensson (1994), people such as Yu (1995), Van Santvoort and Heijmen (1996), people such as Hill (1997)) or a plurality of static field (for example, people such as Galvin (1993), people such as Bortfield (1994)) realize.
US 5663999 discloses a kind of method, and promptly area for treatment can be divided into a plurality of independent treatment subregions.
Obviously, realize that the fastest method that variable dose is treated is the auxilliary simultaneously various piece according to area for treatment.But can't reaching, the system of US 5663999 accomplishes, although it points out that treatment time is a factor that can reduce in theory.Yet, also be difficult to so far maybe can not provide a kind of can be to the algorithm of any treatment section output dose, for no other reason than that available many thin slices collimator must keep the minimum wafer spacing of (for example) 1 centimetre at present.Along with the development of dynamic Therapeutic Method, have necessary with the contacted mode blanking of thin slice part area for treatment.Therefore, some treatment sections can not obtain dosage output, have hindered this broad application.
Summary of the invention
The object of the present invention is to provide a kind of linear accelerator.
According to a kind of linear accelerator of the present invention, comprising:
(1) radiation source, the output of described radiation source are subjected to thin slice collimator more than and another to comprise the restriction of the collimator of two diaphragms at least;
(2) be used for area for treatment is divided into the device of a plurality of sectional arrays, wherein said a plurality of subregions distinguish along the line parallel with described thin slice moving direction;
(3) be used for distributing the device of the dosage of expection to each subregion;
(4) be used for during irradiation, adjusting the position of passing through described thin slice, so that the device of the dosage of expection is provided to each subregion;
Wherein said adjusting device keeps separating of thin slice with the outside that one of them diaphragm extends to one of them described thin slice, and prevents overdosage.
Thus, according to the present invention, diaphragm remains on after the outmost thin slice usually, but also is advanced to outside one or more thin slices sometimes, so that diaphragm provides the predose shielding.This has stoped one or more thin slices to be dropped back effectively, and allows the thin slice on opposite to advance, so that dose limitation is simultaneously again without prejudice to minimum wafer spacing.
Preferably can keep diaphragm to be in after the outmost thin slice fast or be close to after the thin slice, this is because many thin slices collimator has a radiation leaks, thereby diaphragm can limit some radiation leaks.
In this application, suppose that the stretching, extension of the thin slice on a left side is dropped back as the thin slice on the right, field.All direction details will be explained in context.Yet, be understandable that obviously the present invention can be applicable to reverse situation.
Description of drawings
Now by way of example and one embodiment of the present of invention are described with reference to the drawings.Wherein:
Fig. 1 a and 1b show typical discrete intersity modulated beam;
Fig. 2 a and 2b have illustrated minimum wafer spacing to limit;
Fig. 3 has illustrated the composition at control point;
Fig. 4 shows principle flow chart; And
Fig. 5 has illustrated to realize the control point sequence of Fig. 1 a and 1b light beam.
The specific embodiment
Discrete intersity modulated beam herein is used for representing to be divided into the unitary light beam of many penlights, and intensity is constant in each beam unit, but each unitary intensity also may be different.Fig. 1 shows an example.This is the rear-inclined field of a prostate plane graph, and this prostate plane graph has 10% intensity layering and the beam unit of 1cm * 1cm on concentric some plane, and with Corvus design system (for example via NOMOS) drafting plane graph.Fig. 1 a shows the example on gray scale, and Fig. 1 b shows intensity matrix.After this beam unit is called " light element (bixels) " (pixel by image is analogized), typically is 1cm * 1cm in the size of putting with one heart.Oppositely treat design system by some and can calculate discrete intensity modulated.
Realize that by continuous dynamic many thin slice collimations (DMLC) discrete light beams intensity modulated (BIM) have caused some distinctive problems.Particularly, require sudden change along the beam unit of thin slice direction of displacement with intensity.People such as Hill (1997) show before, this can by with leading thin slice with constant speed through a light when plain the oblique descending of intensity of output dose and subsequently thin slice at the same rate by this light when plain the combination of tiltedly going up a slope of the intensity of corresponding output dose realize.Similar stack slope intensity distributions is followed the trail of department (Tracking Cobalt Unit at the Royal Free Hospital, London) middle use (seeing the example of Davy (1985)) by Davy and colleague thereof at London independent hospital of imperial family cobalt.
The algorithm that people such as Hill (1997) provide is the extension of the algorithm of Bortfield et al (1994) use, is used for producing discrete intersity modulated beam by a series of static MLC field of adding up.In these algorithms, the intensity section right along the lattice thin slice is independent check.For each section, the rising and falling edges of intensity pattern matches so that a series of static field to be provided, and these static fields can provide unidirectional " scanning " through the thin slice of visual field in order.In dynamically realizing, people such as Hill (1997) convert this many static fields sequence to a dynamic sequence, in this transition period, thin slice can be maximum speed displacement immobilized or to allow, next, aforesaid oblique descending of intensity and oblique upward slope of stack to provide uniform light plain intensity through the light element.This algorithm is not considered tongue and groove artifact (Van Santvoort and Heijmen (1996)).
The spacing that above-mentioned tenet of dynamic state requires thin slice can be near 0 at the head and tail of this sequence, and the rearmounted thin slice of a thin slice centering can overlap on the adjacent leading thin slice of opposite one row's thin slice.This can not accomplish all many thin slices collimators, and always not wish so that in fact also because mechanical collision can bring hazard, and the contact circle sheet end that uses in some MLC designs can cause leakage.
For many thin slices collimator that the applicant produces, the minimum wafer spacing that dynamic mode allows down is made as 1cm, and this restriction also is applied to relative but adjacent thin slice, so just can not produce thin slice and overlap.With reference to figure 2 (a), the most leading thin slice on the left side not only must keep necessary minimum spacing with the right thin slice on opposite, and also must keep necessary minimum spacing with thin slice upper right, the bottom right.Also to keep same minimum spacing between the standby diaphragm.The width that the MLC thin slice projects to concentric face is 1.0cm, their shift length be from from beam axis 20cm cross center line to 12.5cm.The standby diaphragm of MLC has same shift length, and vertical with it pair of alignment instrument is from moving to center line from beam axis 20cm.The details of Elekta MLC and static field operating characteristic thereof are provided by Jordan and Williams (1994) before this.
By " control point " form of using the dynamic MLC control system of Elekta to use, the dynamic control of explanation MLC thin slice and diaphragm in the algorithm described herein.The specific percentile frame for movement of predetermined light beam monitor unit (MU) (size and shape, gate-type angle, etc.) is determined at the control point.By the definition control point sequence relevant with different monitor unit percentage rate, the dynamic dosage output of definable, as shown in Figure 3.In the Elekta control system, can be in the ideal value of any parameter (as the position of MLC thin slice) of any particular monitored unit fraction values by the fast linear between the control point inserts and obtains in the percentile front and back of this MU.By use MU percentage rate, rather than actual wave beam MU, the dynamic beam scheme does not even need spaced apart control point for the predetermined MU of visual field quick adjustment.
Any light beam must define by two control point at least, one of them control point definition initiating structure (control point O), and a control point definition finishes structure.Can increase the control point of definition intermediate structure.
Except the dynamic beam collimation, this control point form also can be used for defining light beam or light beam section static and only motion.Static light beam section is by having same parameter value but two different continuous control points definition of MU percentage rate, and only motor segment can be by having same MU percentage rate but two different control point realizations of parameter value.During this motion stage, by forbidding that light beam is cut off from the linear accelerator output radiation.Static, dynamically and only the combination of motor segment can mix use in a light beam scheme.
Notice that although a kind of special MLC control system of the special support of this control point form, same notion can be used for other manufacturers' MLC.It shall yet further be noted that the result that the algorithm that this description is described produces is suitable for the realization via how static MLC field equally as what hereinafter will show.
Produce discrete intersity modulated beam by dynamic collimation
Ignore the minimum thin slice of permission or the instantaneous restriction of collimator spacing, be used for to illustrate by considering an isolated beam unit by the basic concept of the discrete intersity modulated beam of dynamic collimation generation.When collimator intermediate plate behind the leading thin slice moves when exposing this unit with constant speed, the oblique descending of intensity is by this unit output dose.Then photograph is evenly assisted in this unit, interdicts this unit up to thin slice subsequently that moves with identical speed with leading thin slice or intermediate plate, and generation provides sharp-pointed, the discrete required necessary strength of initial exposure tiltedly to go up a slope.The basic thought of the technology that people (1997) such as Here it is Hill use.Notice that in unitary beginning of this row and end, thin slice/intermediate plate spacing is required to be 0, so that the light beam edge of sudden change to be provided.
The generation of discrete intersity modulated beam under the minimum spacing restriction
Above-described processing procedure requires can approach 0 at the head and tail thin slice of exposure or the spacing of collimator.We notice that this is impossible concerning all MLC.Yet,, in the dynamic beam scheme, can simulate by the motion of combination MLC thin slice and the motion of reserve diaphragm (collimator intermediate plate) according to the present invention.In this case, thin slice and reserve location of aperture are biased, so that the gap that requires between the MLC thin slice " hides " under the reserve diaphragm, this illustrates in Fig. 2 (b).
Central shield
Central shield promptly shields a zone in the boundary of home court, also can need not thin slice is pressed close to down to realize that during a dynamic exposure in this case, necessary thin slice gap and for example Fig. 2 (b) equally is hidden under the reserve diaphragm of shielding area.
Connotation to the minimum wafer spacing restriction of two-dimentional light beam intensity modulated
The alignment restrictions (Fig. 2 (a)) of minimum wafer spacing restriction, particularly contiguous slices to allowing brought restriction to the synthetic way of output of light beam.Particularly, when producing two dimension (2D) intensity modulated in a light beam, the leading thin slice in a pair of thin slice may need reach to shield a zone, to prevent that this zone is by overexposure.The maintenance of minimum wafer spacing can promote the leading thin slice reach of adjacent a pair of thin slice again, if having only the MLC thin slice to be used to produce synthetic words, will cause the overexposure at this place potentially.Yet if the reserve diaphragm can partly be used as dynamic collimation, so leading thin slice row's reserve diaphragm can be used for providing the shielding of necessity, avoids producing overexposure with regard to allowing leading thin slice reach.Another kind of way is, the initial sheet that may be able to " slow down " is to the generation of intensity distribution down, and thin slice so subsequently is advanced to the back of output sequence, and at this moment it just can not run counter to the right minimum wafer spacing of contiguous slices and limit.This will go through below.
In general, under these minimum wafer spacings restrictions, we find, because such as the influence of above-mentioned " bump (knock on) " effect, the derivation that right thin slice of thin slice moves can not be isolated to its contiguous slices and consider.On the contrary, be necessary to consider together all thin slices of relating to and section, these sections produce all stages of thin slice motion separately.This causes the different schemes of a kind of MLC of being derived from and diaphragm motion again, promptly comes out by the progressive derivation in control point one by one.Thin slice alignment restrictions during in this mode, fully taking into account derivation (location that comprises contiguous slices), and, can eliminate the tongue and groove phenomenon easily as shown in following.This scheme is used for following algorithm.
----oOo----
The plain beam intensity modulation algorithm of light (Bixel BIM) is a kind of principle that iterates, MLC thin slice and the reserve diaphragm motion that is used for deriving, discrete light element (bixel) the intensity modulated field that the wafer spacing of being permitted with output limits.This algorithm by control point one by one derive progressively all thin slices that relate to MLC reserve diaphragm by the time movement locus, rather than consider the derivation that each thin slice is right separately.This algorithm also comprises a kind of device, runs counter to minimum thin slice gap information to derive spendable dynamic aspect by feedback.In the supposition hereinafter, under the situation of not losing its versatility, thin slice and diaphragm from left to right pass this.
When determining that can a light element be assisted photograph at any given control point, adopt two logic matrix (truth table) in the algorithm.First matrix, promptly shielding matrix is to define for each light at each control point is plain.If light element necessary conductively-closed at given control point just is made as " very ", this light element may be by a left side or right MLC thin slice or the shielding of reserve diaphragm.Second matrix, the shielding of promptly right diaphragm is for every row definition of the field at each control point.If it is made as very to a set point, whole these row of light element must be equipped with right back diaphragm (collimator intermediate plate) shielding that is equipped with at this control point so.The state of these matrixes part by desired self intensity distributions definition (for example, any intensity is 0 light element conductively-closed always), but they are also revised continuously as algorithm, be used for correction or prevent that thin slice from colliding or running counter to minimum clearance, avoiding this overexposure zone to occur, and the tongue and groove phenomenon of eliminating the motion of deriving.Notice that by definition, if right diaphragm shielding matrix is classified " very " as to one of any given control point, all light in should being listed as so are plain must conductively-closed.
This algorithm makes the graduation of whole numbers of units of using up plain intensity, and a unit equals the intensity of the interior output dose of time of thin slice or the plain width of light of stop shift.Therefore, the absolute value of this intensity depends on the radiation dose rate that use the width of light element, maximum available wafer spacing and output dose field.Algorithm allows the distance of MLC thin slice and the plain width of light of each control point displacement of diaphragm, and is minimum wafer spacing in the unit representation algorithm with the plain width of light.To go through how the intensity distributions of expecting is mapped as the plain volume unit of light below, and the control of output dose resolution.The form statement that minimum spacing is a unit with the plain width of light.
The principle flow chart of this algorithm as shown in Figure 4.Each key step is described below.
Initialization thin slice and stop position (control point O)
When assisting according to beginning, left thin slice is placed leftmost border on the scene, and right thin slice is positioned at the field with identical minimum spacing (is unit with the plain width of light).The reserve diaphragm is with the spacing that is equal to this minimum light primitive unit cell and the biasing of these thin slices, and like this, right diaphragm is positioned at left margin and left diaphragm is positioned at outside the venue.
The control point circulation
From first control point, use present shielding and right diaphragm shielding matrix position to derive the movement locus that MLC thin slice and diaphragm pass by control point one by one.Thus, following step can be carried out at each control point.
The left back stop position that is equipped with is set
Finish its auxilliary photograph (finding by being checked through so far the intensity that adds up of output dose) if be arranged in plain require at least of any light of at present left back these row that are equipped with the right, stop position more than a control point, diaphragm must still be in the position at former control point so.Otherwise, the plain width of the light that moves right.
Left MLC flap position is set
When this light element (finds by being checked through so far the intensity that adds up of output dose) that when being interdicted at this control point behind its current position a left side (subsequently) MLC thin slice only moves forward.Its auxilliary photograph is finished at least more than one control point if desired, so the position at its maintenance and former control point.
Right MLC flap position is set
For each right MLC thin slice, if require the light element that is exposed by the plain width of light of thin slice displacement to the right in this control point shielding (promptly, shielding at this light element of this control point is " very "), right diaphragm shielding is " vacation ", and the left back diaphragm that is equipped with is not set as this light element of shielding at this control point, is necessary to keep the position of right thin slice at former control point so.Otherwise, the position plain width of light that will move to right again when flap position is than last control point for present control point.
The right back stop position that is equipped with is set
In general, right back stop position fully is set to the position of rightmost MLC thin slice at each control point.Yet if right diaphragm mask logic matrix is made as " very " to this string and control point, so right diaphragm can be provided with so far away.Like this, diaphragm just is used to provide the shielding of necessity at this.Similarly, has the right diaphragm of necessary maintenance border, field on the right, to prevent overdosage outside the venue.
Inspection collision or minimum spacing are run counter to
Check that in this stage thin slice and stop position to guarantee step setting as described above can not cause running counter to the minimum spacing standard, must do individual inspiration to diaphragm spacing and MLC wafer spacing.
At first to check reserve diaphragm spacing, how solve running counter to of MLC wafer spacing because their location can influence.If spacing is permitted spacing less than minimum, the plain width of light of so right diaphragm reach just just in time can shield thereon row (by the indication of diaphragm mask logic matrix) up to this diaphragm, and in this case, left diaphragm must be return the plain width of a light on the contrary.If left diaphragm is returned, be necessary further to check this light element whether this diaphragm of the meeting of following overexposure has shielded so.If find this just situation, the right diaphragm shielding that these row are set so restarts to consider these fresh informations for " very " up to current control point and motion derivation algorithm.
In case check to finish the back stop position and finished necessary correction, just can estimate the position of MLC thin slice.(second portion) is such just as noted, and for the design such as ElektaMLC, it is right that minimum spacing requires not only to be applied to every single sheet, and is applied to the position of contiguous slices, therefore also must check the position of each contiguous slices.
According to this example, be in sequence to the wafer spacing inspection of each right thin slice.This is checked and also is applicable to each left thin slice certainly.
If left thin slice and right thin slice within minimum spacing, will determine to move left thin slice so or right thin slice is corrected check result.
If the current just in time light element on right thin slice end does not need shielding at this control point, if perhaps it does not need shielding and still is provided with right diaphragm shielding, right diaphragm so can move forward.
If do not use these conditions, must carry out a detection so, see this point that whether can arrive soon after (this can accomplish by the right thin slice motion of forbidding being correlated with), stop this generation of running counter to the situation of distance limit by the left thin slice of in scheme, forcing to be correlated with.For reaching this purpose, return each row and iterate inspection to seek first control point, at this control point, the light beam under the left thin slice is exposed, and estimates right thin slice return and shield the minimum thin slice requirement whether this position can run counter to this control point.If possible forbid left thin slice by this way, the logic matrix shielding is corrected thus so, and the movement locus of deriving again also can be taken into account it.(, before shielding changes for the first time, derive and continue) from this control point for raising the efficiency.
If can not forbid advancing of left thin slice by this way, so right thin slice must be moved forward, and shield this light element (and arriving whole row thus) by the shielding of right diaphragm being made as the right diaphragm of " very " pressure, up to this control point and the movement locus of deriving again.Owing to can cause the efficient of this dosage output scheme not high like this (diaphragm shields all outside this point), if this method only is used in the time of can not forbidding whether right thin slice moves (as above-mentioned).
Inspection does not have right thin slice too far away under right diaphragm
After minimum spacing inspection (as above-mentioned) and adjustment finish, then check whether to have any right backly to be equipped with right thin slice under the diaphragm unnecessarily too away from diaphragm.If the certain mistake of distance is far away and position this control point can be adjusted, and without prejudice to the minimum clearance standard, redefines their position so.Taking this step is in order to minimize the radiation leaks via the reserve diaphragm.
Inspection does not have light plain by excessively auxilliary photograph
After the desired adjustment of minimum spacing condition executes, check that and then do not have the light procatarxis is current thin slice and location of aperture and by excessively auxilliary photograph, this for example may occur in, if right thin slice has moved forward when preventing to run counter to the minimum spacing condition.Plain the mask logic matrix is made as " very " with this light element all control point up to the present by excessively auxilliary photograph if light is arranged, and considers this updated information movement locus of deriving again.Equally, for raising the efficiency, before changing the first time of shielding, derive and continue from this control point.
Check the intensity that adds up of output dose
Whether the inspection intensity that adds up correctly outputs to all light elements.If situation is true, optionally check the intensity in tongue and groove zone (following) between thin slice.If no, then need an above control point at least, and continue the circulation at control point.
Inspection tongue and groove zone
Also optionally check when derive in each control point the intensity in tongue and groove zone between thin slice.If find that light exposure is low excessively, just can correct (VanSantvoort and Heijmen (1996)) to moving by forbidding the most leading thin slice.In this algorithm, be by seeking the control point the earliest that the relative photo element is exposed, and the shielding at N control point of this light element that will begin from this control point is made as that " very " realize, herein, the output dose by this N control point is corresponding to the tongue and groove of the under-exposure of discovery.By considering this lastest imformation movement locus of deriving again, and, before changing the first time of shielding, derive and continue from this control point as the front.
Yet should note, the maintenance of minimum wafer spacing is tending towards and the thin slice synchronized movement with the relevant routine of avoiding colliding, so that the under-exposure in zone can not produce big variation to the dosage output scheme between thin slice, and concerning whole dosage output, usually can not involve any additional control point (producing additional MU thus).
Use aforementioned algorithm and the results are shown in Figure 5, the MLC structure that there is shown at each control point to the distribution example of Fig. 1.The zone of black is simultaneously by the zone of MLC thin slice and the shielding of reserve diaphragm, and dark-grey zone is only shielded by the MLC thin slice, and the zone of light gray only is backlogged the diaphragm shielding.Light element (beam unit) is of a size of 1cm * 1cm, and minimum thin slice/diaphragm spacing is appointed as 1cm.Can see clearly that dosage output beginning that sharp-pointed edge, field requires and the enclosed construction that finishes also can be seen shielding is provided when using the reserve diaphragm to restrict flap position with the restriction at minimum wafer spacing.It should be noted that equally that as above-described thin slice and diaphragm are restricted to and can only move the plain width of a light in every control point.
Above-mentioned algorithm realizes being used to export the discrete light beams intensity modulated having on the Phillips/Elekta SL25 of MLC.A theory diagram of this realization is seen Fig. 6, below its principal character will be discussed.
The intensity distribution that converts and import
Input intensity distribution (certainly demarcating arbitrarily) converts according to " nominal standard dose " of field output.Doing like this is in order to control the intensity distributions resolution of output dose, and the dynamic beam scheme when guaranteeing dosage output can not require to surpass the web speed (seeing below) that MLC has.This result can regard monitor unit as and distribute, and specifies each unit of MU light beam to receive.Yet it should be noted that the explicit value that is used for nominal standard dose is undemanding (it is only with for referencial use),, therefore can convert with the monitor unit that presets because light beam scheme file is based on the percentile control point of monitor unit each point.
Open field assembly output dose
On the scene is not that it is to export some or all of field basic intensity levels by a static field assembly that this realizations also has a selection under the situation of blocking of center.This will allow the conventional planning treatment to change the portal imaging of patient position down, and allow most of field intensity by big relatively static field output, concerning static field, radiation dose rate meter is more common, and concerning static field, for example the patient moves that wrong consequence is set is just so not serious with thin slice.When selecting this option, static field (with suitable MU percentage rate) is specified at preceding two control point.Be an only mobile step subsequently, in the meantime, light beam is closed, and the border, field that the MLC thin slice moves to left produces dynamic modulation afterwards in the step of ensuing control point.
The resolution that control dosage output intensity distributes
" substantially " strength distinguish rate of dosage in this scheme output is subjected to thin slice or diaphragm to pass the control of output intensity during beam unit (light element) width.This depends on the maximum web speed that allows, and depends on the close rate of this output, and depends on cell width.For example, concerning the wide beam unit of 1cm, with the velocity process of 400MU/ minute and maximum web speed 1cm/ second, the result produces the base resolution of the 6.67MU that releases, that is, and and ± 3.3MU.Monitor unit distributes (that is, the intensity distribution of conversion) then around arriving nearest MU/ light element, to produce the inner beam intensity unit matrix that uses of algorithm.
Yet, only need just can improve the resolution of this dosage output easily by before turning round, segmenting necessarily along the beam unit in the original distribution of thin slice direction of displacement.In the above example, if the wide unit of 1cm is subdivided into 3.3mm, consequent dosage output resolution ratio will improve ± 1.1MU.The cost of doing like this is that the control that the requirement increase is used for defining dynamic aspect is counted.Yet it does not influence the MLC delivery efficiency,, requires to be used for the MU quantity of output field that is.
In aforementioned algorithm, only considered primary intensity (contribution of the limited transmission by thin slice and diaphragm), do not comprise the head scattering radiation and away from the variation of the primary intensity of central shaft.The purpose of doing so only provides the portable algorithm of considering based on how much, and it is not subjected to the influence that changes between the machine, the influence of yet not calculated the method for above-mentioned quantity.On the contrary, these additive factorss can include by this algorithm is embedded in the iterative cycles, (Convery and Webb (1997)) as described below:
1. use above-mentioned algorithm (only considering how much) to calculate thin slice and diaphragm motion.
2. use move dosage under the reference conditions of calculating overall strength or requirement of this thin slice.If the difference of value of calculation and desired value is released iterative cycles so, otherwise is proceeded to step 3 greater than default limit (if or subsequent iteration do not bring any improvement).
3. calculate the input intensity distribution of a correction based on the difference of value of calculation and desired value.
4. use of the input of the intensity distributions of this correction as this algorithm---begin repetition from step 1.
What more should be noted that is, by dividing radiation dose from the actual derivation of MLC motion, this algorithm becomes and is independent of the modulation quantity of our actual consideration, for example, this may be face (" in air with one heart ") overall strength of influence, the dosage, the dosage of some reference depth under specified reference conditions of the peak depth of face with one heart, or some other quantity.The application of this algorithm also is independent of the method for calculating these quantity, to such an extent as to it can need not to be used for different planning systems or software module with changing, has therefore guaranteed transposability and application widely.
Although the initial exploitation of this algorithm of describing is in order to produce the dynamic collimation system, be used for the output of discrete light beams intensity modulated field, but from Fig. 5 as seen, its output can be described as static MLC field sequence (by the control point organization definition, not comprising those motion beginnings and the control point of finishing) equally well.Because initial designs is to be dynamic realization, the beam broken time that relates to during stepping between each field structure can be very little.Unique variation that this algorithm requires is that each derivation step conduct of record is followed the static control point of a movement step to arriving next field structure.This may, for example under the situation of the complete dynamically control that is not having MLC, be necessary.
Many static field outputs also may be preferred, because this is the littler step away from the output of traditional radiation therapy dosage.The dosage measurement of these light beams is easier, and as their QA and calibration, and they therefore may be easier of clinical acceptance.
Although technology described here (derive and move one by one by the control point, thin slice collision correction/prevention process, use the part of reserve diaphragm as the dynamic collimation process) be under dynamic dosage output system environment, to develop for discrete modulated beam of light, but they also can be applicable to produce continuously (that is, non-discrete) modulation.
List of references
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Convey?D?J?and?Webb?S?1997?Calculation?of?the?distribution?ofhead-scattered?radiation?in?dynamically-collimated?MLC?firlds?Proc12th?Int?Conf?Computers?in?Radiotherapy，Utah，May?1997(Ed.LeavittDD?and?Starkschall?G)，pp?350-353
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Claims (4)
1. linear accelerator comprises:
(1) radiation source, the output of described radiation source are subjected to thin slice collimator more than and another to comprise the restriction of the collimator of two diaphragms at least;
(2) be used for area for treatment is divided into the device of a plurality of sectional arrays, wherein said a plurality of subregions distinguish along the line parallel with described thin slice moving direction;
(3) be used for distributing the device of the dosage of expection to each subregion;
(4) be used for during irradiation, adjusting the position of passing through described thin slice, so that the device of the dosage of expection is provided to each subregion;
Wherein said adjusting device keeps separating of thin slice with the outside that one of them diaphragm extends to one of them described thin slice, and prevents overdosage.
2. according to the accelerator of claim 1, wherein said accelerator remains on the outside of the outermost thin slice of seeing from the exposure beam direction in order to treatment with described diaphragm.
3. according to the accelerator of claim 1, wherein said accelerator is advanced to one or more diaphragms outside one or more thin slices, so that described diaphragm provides the predose shielding.
4. according to the accelerator of claim 1, wherein said accelerator also is used for described diaphragm being remained on the outside of the outermost thin slice of seeing from the exposure beam angle or being close to thereafter.
Applications Claiming Priority (2)
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| GB9806057A GB2335583B (en) | 1998-03-20 | 1998-03-20 | Controlling delivery of radiotherapy |
| GB9806057.7 | 1998-03-20 |
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| CN1202884C true CN1202884C (en) | 2005-05-25 |
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| JP (1) | JP2002507462A (en) |
| KR (1) | KR20010042049A (en) |
| CN (1) | CN1202884C (en) |
| CA (1) | CA2324446A1 (en) |
| GB (1) | GB2335583B (en) |
| WO (1) | WO1999048558A1 (en) |
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| US6134296A (en) * | 1999-01-20 | 2000-10-17 | Siemens Medical Systems, Inc. | Microgradient intensity modulating multi-leaf collimator |
| US6260999B1 (en) * | 1999-07-26 | 2001-07-17 | Siemens Medical Systems, Inc. | Isocenter localization using electronic portal imaging |
| US6477229B1 (en) | 2000-05-12 | 2002-11-05 | Siemens Medical Solutions Usa, Inc. | Radiation therapy planning |
| GB2370210B (en) * | 2000-12-13 | 2004-06-02 | Elekta Ab | Radiotherapeutic apparatus |
| US6687330B2 (en) * | 2001-07-31 | 2004-02-03 | Siemens Medical Solutions Usa, Inc. | System and method for intensity modulated radiation therapy |
| US6907105B2 (en) | 2001-09-25 | 2005-06-14 | Bc Cancer Agency | Methods and apparatus for planning and delivering intensity modulated radiation fields with a rotating multileaf collimator |
| US6661871B2 (en) * | 2001-09-28 | 2003-12-09 | Siemens Medical Solutions Usa, Inc. | System and method for optimizing radiation treatment with an intensity modulating multi-leaf collimator by minimizing junctions |
| US6839405B2 (en) | 2002-05-31 | 2005-01-04 | Siemens Medical Solutions Usa, Inc. | System and method for electronic shaping of X-ray beams |
| GB0310596D0 (en) * | 2003-05-08 | 2003-06-11 | Cancer Res Inst | Method and apparatus for producing an intensity modulated beam of radiation |
| US7085348B2 (en) * | 2003-12-15 | 2006-08-01 | The University Of Florida Research Foundation, Inc. | Leaf sequencing method and system |
| US9498167B2 (en) | 2005-04-29 | 2016-11-22 | Varian Medical Systems, Inc. | System and methods for treating patients using radiation |
| US7734010B2 (en) | 2005-05-13 | 2010-06-08 | Bc Cancer Agency | Method and apparatus for planning and delivering radiation treatment |
| EP1909904B1 (en) | 2005-07-25 | 2013-09-04 | Karl Otto | Methods and apparatus for the planning of radiation treatments |
| US7880154B2 (en) | 2005-07-25 | 2011-02-01 | Karl Otto | Methods and apparatus for the planning and delivery of radiation treatments |
| CA2657791A1 (en) | 2006-07-27 | 2008-01-31 | British Columbia Cancer Agency Branch | Systems and methods for optimization of on-line adaptive radiation therapy |
| US8699664B2 (en) | 2006-07-27 | 2014-04-15 | British Columbia Center Agency Branch | Systems and methods for optimization of on-line adaptive radiation therapy |
| WO2008063573A2 (en) | 2006-11-17 | 2008-05-29 | Varian Medical Systems Technologies, Inc. | Dynamic patient positioning system |
| USRE46953E1 (en) | 2007-04-20 | 2018-07-17 | University Of Maryland, Baltimore | Single-arc dose painting for precision radiation therapy |
| EP2585854B1 (en) | 2010-06-22 | 2020-03-18 | Varian Medical Systems International AG | System and method for estimating and manipulating estimated radiation dose |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| US3448270A (en) * | 1966-11-23 | 1969-06-03 | Machlett Lab Inc | X-ray collimating device wherein a plurality of adjustable overlapping leaves define a collimating cone |
| US4868843A (en) * | 1986-09-10 | 1989-09-19 | Varian Associates, Inc. | Multileaf collimator and compensator for radiotherapy machines |
| GB2211710A (en) * | 1987-10-28 | 1989-07-05 | Philips Nv | Multileaf collimator |
| US5663999A (en) * | 1996-06-28 | 1997-09-02 | Systems Medical Systems, Inc. | Optimization of an intensity modulated field |
| US5757881A (en) * | 1997-01-06 | 1998-05-26 | Siemens Business Communication Systems, Inc. | Redundant field-defining arrays for a radiation system |
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- 1999-03-19 CA CA002324446A patent/CA2324446A1/en not_active Abandoned
- 1999-03-19 KR KR1020007010391A patent/KR20010042049A/en not_active Application Discontinuation
- 1999-03-19 EP EP99911913A patent/EP1064051A1/en not_active Withdrawn
- 1999-03-19 WO PCT/GB1999/000886 patent/WO1999048558A1/en not_active Application Discontinuation
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| GB2335583A (en) | 1999-09-22 |
| GB2335583B (en) | 2002-05-29 |
| CA2324446A1 (en) | 1999-09-30 |
| KR20010042049A (en) | 2001-05-25 |
| GB9806057D0 (en) | 1998-05-20 |
| JP2002507462A (en) | 2002-03-12 |
| WO1999048558A1 (en) | 1999-09-30 |
| EP1064051A1 (en) | 2001-01-03 |
| CN1298317A (en) | 2001-06-06 |
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