Leaf sequencing

Systems and methods of controlling the leaves of an aperture in radiation treatment are disclosed. In some embodiments, these systems and methods allow the delivery of different radiation fluences to different parts of a treatment volume in a single rotation of the aperture around the treatment volume. In some embodiments, different radiation fluences are achieved by radiating different parts of the treatment volume from opposing positions of the aperture around the treatment volume. In some embodiments, different radiation fluences are achieved by assigning different leaf pairs to radiate different parts of the treatment volume.

BACKGROUND

1. Field of the Invention

The invention is in the field of radiation therapy and more specifically related to the use of leaf apertures to control delivery of radiation to a patient.

2. Related Art

Radiation, e.g., x-rays or particle beams, is used in a variety of medical treatments. Preferably, radiation is delivered to a treatment volume and not to a surrounding region of healthy tissue. In order to achieve these treatment preferences, a radiation beam is typically shaped using an aperture. The aperture is configured to shape the radiation beam according to a geometric projection of the treatment volume along the axis of the radiation beam.

One type of aperture includes a series of movable leaves. These leaves may be comprised of a series of thin plates whose thin dimension and axis of movement are both perpendicular to the direction of the radiation beam. Movement of the leaves allows for the generation of a variety of openings and, thus, a variety of radiation beam shapes. The resolution of these shapes is, in part, dependent on the thickness and number of the plates.

In some treatment schemes, a radiation source and aperture are rotated around the treatment volume, i.e., around a patient, using a gantry. One advantage of this approach is that the radiation beam does not always pass through the same healthy tissue. For example, at two different points in the rotation process, the radiation beam may be directed at the treatment volume from directions that differ by approximately ninety degrees. While the radiation beam passes through the treatment volume from both directions, it passes through different parts of the healthy tissue from the different directions. As such, the harmful impacts on the healthy tissue are distributed and their total magnitude reduced.

In the prior art, the rotating radiation source and aperture are configured to provide a single fluence. The fluence is a two-dimensional object defined in a plane. An intensity is defined at each point of fluence. The intensity is the amount of radiation per unit cross-sectional area. The magnitude of the fluence may take any of a range of continuous values. However, magnitude of the fluence is typically approximated by discrete fluence levels, i.e. the continuous fluence values are mapped to a set of discrete values.

The fluence is distinct from dose which is the total radiation received by a part of the treatment volume. The dose is a three-dimensional distribution whose magnitude varies as a function of the position within the treatment volume. This variation may be undesirable. In the prior art, improved control over the three-dimensional dose distribution inside the treatment volume may be achieved by rotating the aperture around the treatment volume more than one time. The intensity and spatial distribution of radiation provided by a beam source is changed between consecutive rotations. This may be accomplished, for example, by changing the shape of an aperture within the beam source. The availability of more than one fluence per position along the trajectory of the rotation allows for improved control over the dose distribution. However, this approach results in a variety of disadvantages, for example, rotation of the aperture more than once around the treatment volume requires additional time.

When the radiation source and aperture are rotated around a treatment volume, the projection of the treatment volume onto the aperture may change. As such, it is desirable to change the opening within the aperture as the aperture is moved though different angles. These changes are typically achieved by moving leaves within the aperture to positions determined prior to the treatment. There are several ways in which leaf positions may be determined. In one approach, the projection of the treatment volume along the axis of the radiation beam is determined at each position along the arc of rotation. Two points along the arc of rotation approximately 180 degrees apart will have essentially the same projections (e.g., a mirror image thereof) and, therefore, essentially the same relative leaf configurations. Radiation generated by a beam source is typically constant as the aperture is rotated around the treatment volume. The amount of radiation received by various parts of the treatment volume is, therefore, primarily controlled by the aperture.

One approach to determining leaf positions that can include consideration of the dose received by each part of the treatment volume includes selecting a particular set of leaf positions, for example, by using projections of the treatment volume. The dose distribution throughout the treatment volume is then calculated. After this calculation, the selected set of leaf positions is changed slightly and the projected dose distribution is again calculated. If the change in leaf positions results in an improvement in the dose, the changed leaf positions are kept and the process is repeated. This iterative process may be facilitated by statistical or optimization algorithms. Disadvantages with this approach include lengthy computation times.

SUMMARY

Various embodiments of the invention include systems and methods of managing the positions of aperture leafs so as to improve the radiation treatment of patients. In some embodiments, these systems and methods allow for improved control over the dose received in the treatment volume. In some embodiments, these systems and methods allow for the selection and use of several different discrete fluence levels in a single treatment. For example, leaves may be controlled such that a first part of the treatment volume receives a first amount of radiation and a second part of the treatment volume receives half of the first amount. These parts of the treatment volume and/or the dosage they receive can be designated by a user.

In some embodiments, different leaf configurations are used at opposing points around an arc of rotation to effectively deliver more than one discrete fluence level. For example, in a first position the leaves may be configured to deliver radiation to a first subset of the treatment volume and in a second position, 180 degrees from the first position, the leaves may be configured to deliver the radiation to a second subset of the treatment volume. Those parts of the treatment volume that are included in both the first subset and the second subset receive twice the radiation dose relative to those parts that are included in only one of the first subset and the second subset.

In some embodiments, more than one radiation fluence level is provided by dividing aperture leaves into two or more groups, configuring a first of the two or more groups to provide radiation to a first subset of the treatment volume and configuring a second of the two or more groups to provide the radiation to a second subset of the treatment volume. Those parts of the treatment volume that are included in both the first subset and the second subset receive twice the radiation dose relative to those parts that are included in only one of the first subset and the second subset. Thus, more than one fluence level can be provided at the same time.

The approaches for producing multiple discrete fluence levels per position along the arc of rotation can be used in combination. For example, four discrete fluence levels can be generated by both using different leaf configurations at opposing arc points and by dividing aperture leafs into two or more groups.

Various embodiments of the invention include a radiation treatment system comprising a beam source configured to generate a beam of radiation, a beam aperture including a plurality of aperture leaves configured to shape the beam of radiation, a gantry configured to move the beam aperture, and a computing device configured to control the plurality of aperture leaves so as to provide a dose distribution within a treatment volume while moving the beam aperture 360 degrees or less around the treatment volume using the gantry.

Various embodiments of the invention include a method of determining a configuration of a radiation treatment system, the method comprising receiving a plurality of optimal fluences to be delivered to the treatment volume, the optimal fluences being configured to provide a dose distribution within the treatment volume, determining a plurality of discrete fluence levels to be delivered to the treatment volume, the plurality of discrete fluence levels being determined so as to approximate the optimal fluences, and calculating leaf positions for each leaf of a beam aperture at each of a plurality of beam aperture positions in order to achieve the plurality of discrete fluence levels by moving the beam aperture one or fewer times around an arc of rotation.

Various embodiments of the invention include a computing system comprising a fluence determination engine configured to determine a plurality of radiation fluence levels to produce a desired dose distribution, a leaf position calculator configured to calculate leaf positions for a plurality of leaves in a radiation beam aperture, the leaf positions being configured to provide the plurality of radiation fluence levels to a treatment volume within one rotation of the radiation beam aperture around the treatment volume, and a leaf controller configured to control the plurality of leaves according to the leaf positions calculated using the leaf position calculator.

DETAILED DESCRIPTION

The invention includes systems and methods for providing radiation treatment to a patient. These systems and methods include, for example, a beam source configured to provide a beam of therapeutic radiation. The beam of radiation is shaped by an aperture that is moved, e.g., rotated, around a treatment volume using a gantry. The treatment volume may include a tumor or other part of a patient that benefits from the therapeutic radiation. Some embodiments further include a computing device configured to determine optimum positions for leaves within the aperture. These optimum positions may be configured to provide more than one discrete fluence level during one (or fewer) complete rotation of the aperture around the gantry. Various embodiments of the invention include alternative approaches to providing multiple discrete fluence levels. As is further described herein, some of these approaches may be used in combination.

FIG. 1illustrates a cross-section of an exemplary Treatment Volume100. This cross-section may be projected to an aperture along the direction of a radiation beam. As the position of the aperture changes, the projection of the projected cross-section is also likely to change according to the three-dimensional shape of Treatment Volume100. In some embodiments, Treatment Volume100includes more than one separate volume. For example, Treatment Volume100may include two separate tumors separated by healthy tissue. In some embodiments, the treatment volume surrounds a volume of healthy tissue. For example, Treatment Volume100may include a tumor that has grown around a healthy tissue. The shape of Treatment Volume100shown inFIG. 1is an arbitrary shape used for illustrative purposes. Treatment Volume100may take a wide variety of shapes and, thus, result in a wide variety of cross-sections.

FIG. 2illustrates an Aperture200configured to shape a radiation beam to match Treatment Volume100illustrated inFIG. 1, according to various embodiments of the invention. Aperture200includes a plurality of movable Leaves210, some of which are individually designated210A-210F. Each of Leaves210typically includes a plate having a thickness in the direction parallel to the radiation beam (perpendicular to the image ofFIG. 2) that is sufficient to greatly attenuate that part of the radiation beam that is blocked by one of Leaves210. Opposing members of Leaves210are referred to as Leaf Pairs230. For example, Leaves210A and210B comprise a Leaf Pair230A. Likewise, Leaves210C and210D comprise a Leaf Pair230B.

Leaves210may be moved in Directions220in order to provide one or more Opening240. For example, inFIG. 2Leaf Pair230A is disposed to match the projection of Treatment Volume100along the direction of the radiation beam to Aperture200. Opening240may include a single opening as illustrated inFIG. 2, or a plurality of separate openings as illustrated elsewhere herein. In some embodiments, Aperture200can be rotated within the plane of the figure, e.g., in Directions250.

FIG. 3illustrates a Radiation Treatment System, generally designated300and including a 360 degree Gantry310configured to support and move Aperture200ofFIG. 2. Gantry310is configured to move Aperture200and optionally part of a beam source (not shown) in directions320. As Aperture200is moved around Treatment Volume100, the beam of radiation travels from Aperture200to Treatment Volume100from a variety of directions. For example, at the position of Aperture200illustrated inFIG. 3, a radiation beam is directed in a Direction330.

As Aperture200is moved around Treatment Volume100, the projection of Treatment Volume100onto Aperture200changes according to the three-dimensional shape of the Treatment Volume100. As is further described herein, this changing projection is one of the factors that may be used to determine a position for leaves210. The projection of Treatment Volume100will be approximately the same when Aperture200is positioned in opposing positions around Gantry310. For example, the projections from a Position340and a Position350will be approximately the same. For the purposes of this discussion, these positions are referred to herein as the 11:00 and 5:00 positions respectively. Likewise, a Position360and a Position370are referred to herein as the 3:00 and 9:00 positions respectively. Other positions may be referred to herein using similar clock based references.

FIG. 4is a block diagram of Radiation Treatment System300, which includes a Beam Source410, Beam Aperture200and Gantry310. Beam Source410is configured to generate a beam of therapeutic radiation. This beam of radiation may include x-rays, particles, and/or the like. For example, in some embodiments, Beam Source410includes an x-ray source. In some embodiments, Beam Source410includes a particle beam source such as a particle accelerator. Beam Source410is optionally configured for generating imaging radiation as well as therapeutic radiation.

Radiation Treatment System300further includes a Computing Device420configured to determine radiation fluence levels using a Fluence Determination Engine430, to send signals to Beam Aperture200to position Leaves210using a Leaf Controller440, and to calculate leaf positions using a Leaf Position Calculator450.

Computing Device420typically further comprises a Processor460and Memory470. Processor460is configured to execute computing instructions in order to perform methods and functions described herein. These computing instructions may be embodied in hardware, firmware, and/or software. Memory470is configured to store the computing instructions, data related to the three-dimensional dose distribution, data related to fluences, data defining the treatment zone, calculated leaf positions, and/or the like. Computing Device420may further include a User Interface480. User Interface480may include a display and/or a graphical user interface, and is configured for a user to control Radiation Treatment System300, designate fluence levels, designate a treatment volume, and/or the like.

Fluence Determination Engine430is configured for determining a plurality of optimal fluences appropriate for achieving a desired three-dimensional dose distribution within a treatment volume. These optimal fluences are optionally continuous rather than discrete. For example, in some embodiments, Fluence Determination Engine430is configured to receive specifications for a desired three-dimensional dose distribution from a user via User Interface480. The spatial characteristics of the desired three-dimensional dose distribution may be designated manually by having the user mark boundaries of the spatial distribution on an image of Treatment Volume100. Alternatively, the spatial distribution may be automatically designated by applying a filter to an image of Treatment Volume100. For example, the spatial distribution may be designated by selecting image pixels within a certain intensity range. Designation of the spatial distribution may include both manual and automated approaches. Typically, the spatial distribution is selected to avoid delivering radiation to healthy radiation sensitive organs.

FIG. 5Aillustrates a plurality of discrete fluence levels (solid line), approximating the optimal fluences (dotted line) as may be appropriate for an exemplary treatment. InFIG. 5A, the X-axis510represents position within a cross-section of Aperture200and the Y-axis520represents a normalized magnitude of the fluence. The magnitude of the optimal fluences is represented by a Dashed Line530. As shown inFIG. 5A, the magnitude of the fluence varies as a function of position. Between a Position540A and a Position540B, and a Position540D and a Position540E, the discrete fluence level is approximately ¼ of the Maximum Discrete Fluence550. Between Position540B and a Position540C, the discrete fluence level is approximately equal to the Maximum Discrete Fluence550. Between Position540C and the Position540D, the discrete fluence level is approximately ¾ of the Maximum Discrete Fluence550. In some embodiments, Fluence Determination Engine430is configured to calculate the continuous fluences in order to achieve a desired three-dimensional dose distribution for each point within the Treatment Volume100.

The optimal fluences are used, by the Fluence Determination Engine430, to determine the plurality of discrete fluence levels. The discrete fluence levels are typically selected so as to best approximate the optimal fluences. For example, inFIG. 5A, the selected discrete fluence levels are illustrated by Solid Line560. These discrete fluence levels are selected to approximate the optimal fluences illustrated by Dashed Line530. Because the optimal fluences may vary as a function of gantry angle, Fluence Determination Engine430is optionally configured to select a different set of discrete fluence levels for each gantry angle. The selection of discrete fluence levels may be manual or automatic.

In some embodiments, determined discrete fluence levels from opposing gantry positions are summed or averaged. This can significantly simplify the determination of the discrete fluence levels. Summing or averaging the discrete fluence levels from opposing gantry positions is possible because the projection of Treatment Volume100in opposite directions is approximately the same. (These projections are not necessarily exactly the same because the radiation beam typically has some divergence.)

As is described further herein, the discrete fluences levels are sometimes restricted to being simple ratios of each other. For example, the discrete fluence levels may be in ratios of 1:½, 1:¼, 1:¾, 1:⅓, 1:⅔, and/or the like. Further, more than two fluence levels may be selected for use during a single movement around Gantry310. For example,FIG. 5Aillustrates three discrete fluence levels in ratios of 1:¾, 1:¼ and 1:⅓. (The discrete fluence levels in the ratio of 1:⅓ can be found by comparing the fluence between Positions540C and540D to the fluence between Positions540D and540E.) A greater number of discrete fluence levels can allow for an improved approximation of the optimal fluences. For example, using the three discrete fluence levels illustrated inFIG. 5A, between Positions540A and540B the discrete fluence level is substantially below the optimal fluences. A fourth discrete fluence level of approximately ⅜ of the Maximum Discrete Fluence550would allow a better approximation in this particular example.

FIG. 5Billustrates an alternative shape of the optimal fluences and corresponding discrete fluence levels. These discrete fluence levels include a region, between a Position540F and a Position540G, in which the optimal fluences are approximated with a discrete fluence level of zero. Such a distribution may be desirable to protect radiation sensitive organs, e.g. a spinal cord. Typically, a greater the number of discrete fluence levels allows for a better the match between the discrete fluence levels and the optimal fluences.

Referring again toFIG. 4, Leaf Controller440is configured to send control signals to Beam Aperture200so as to move Leaves210to the leaf positions calculated using Leaf Position Calculator450. In some embodiments, these control signals include digital data to be delivered to Beam Aperture220. Leaf Controller440may include computing instructions and/or hardware configured for communication and signal processing.

Leaf Position Calculator450is configured to calculate positions for each Leaf210at each position of Gantry310. These leaf positions are calculated so as to achieve the discrete fluence levels selected using Fluence Determination Engine430. Typically, Leaf Position Calculator450starts the calculation of leaf positions by a) assigning Leaves210to different groups, and/or b) by assigning different positions of Aperture200(relative to Gantry310) to different groups. Thus, groups may include sets of Leaves210and/or sets of positions of Aperture200. In some embodiments, Leaves210are assigned on the basis of Leaf Pairs230. For example, each opposing Leaf Pair230may be assigned together to a group. Each group is configured to provide radiation to a different volume within Treatment Volume100. Further details of these assignments are discussed elsewhere herein.

FIGS. 6A-6Dare an illustration of how different groups (of Leaves210and/or positions) can be used to provide a plurality of discrete fluence levels.FIG. 6Ashows an Area610A that will be radiated using a first group andFIG. 6Bshows an Area610B to be radiated using a second group. These areas are in a plane through Treatment Volume100and perpendicular to the direction of the radiation beam. For example, in the example illustrated inFIG. 3, if the Aperture were in the 11:00 Position340, the plane through Treatment Volume100would be perpendicular to the Direction330. During a single movement of Aperture200around Gantry310the radiation generated using Beam Source410is approximately constant, as such, each of Area610A and610B receive the same fluence of radiation. For the purposes of illustration, this fluence can be referred to as fluence “X.”

FIG. 6Cshows the combined effects of radiation received by the Treatment Volume100due to both the first group and the second group. Some parts of Treatment Volume100receive radiation only as a result of the first group, some parts of Treatment Volume100receive radiation only as a result of the second group, and some parts of the Treatment Volume100(illustrated by Hash Marks620) receive radiation as a result of both the first group and the second group. Those parts of Treatment Volume100that receive radiation only as a result of one group receive a fluence of level “X,” while those parts of Treatment Volume100that receive radiation as a result of both groups receive a fluence of level “2X.” As such, two different discrete fluence levels are achieved in a ratio of 1:½. More than two groups may be used to achieve more than two discrete fluence levels. For example, in some embodiments, two groups are established by assignment of Leaf Pairs230and two groups are established by assignment of positions of Aperture200. These two groups may be used to achieve two, three or four discrete fluence levels.

FIG. 6Dillustrates the discrete fluence levels resulting from the groups illustrated inFIG. 6Calong a Cross-section630. As shown, in some Positions640a fluence of “X” is achieved while in other Positions650a fluence of “2X” is achieved. More than two groups may be used to achieve more than two discrete fluence levels.

FIGS. 7A-7Fillustrate further examples of how different groupings can be used to generate multiple discrete fluence levels.FIGS. 7A and 7Billustrate fluence magnitude as a function of position along a cross-section such as Cross-section630.FIG. 7Aillustrates the fluence resulting from a first group whileFIG. 7Billustrates the fluence resulting from a second group.FIG. 7Cillustrates the combined fluence that can be achieved using the first and second group in a single movement of Beam Aperture200around Gantry310. Likewise,FIGS. 7D and 7Eillustrate fluences resulting from a third group and a fourth group, respectively. More than one leaf pair assigned to separate groups are required to generate a fluence including a gap such as that illustrated inFIGS. 7D and 7E.FIG. 7Fillustrates the combined fluence that can be achieved using the third and fourth groups in a single movement (rotation) of Beam Aperture200around Gantry310.

In some embodiments, Leaf Position Calculator450is configured to assign different positions of Aperture200around Gantry310to different groups each configured to provide radiation to a different part, e.g. subset, of Treatment Volume100. For example, the 11:00 o'clock Position340may be assigned to a first group and the 5:00 o'clock Position350may be assigned to a second group. As a result of these assignments, at the 11:00 o'clock Position340, as shown inFIG. 3, Leaf Pairs230will be configured to deliver radiation to a first part of Treatment Volume100, and at the 5:00 o'clock Position350Leaf Pairs230will be configured to deliver radiation to a second part of Treatment Volume100. As illustrated inFIGS. 6A-6Dand7A-7F, these parts of Treatment Volume100may overlap to achieve multiple discrete fluence levels. This approach is different than the prior art wherein relative leaf positions at opposing points around Gantry310are typically the mirror image of each other so as to radiate the same part of a treatment volume. Each pair of opposing positions around Gantry310is optionally assigned to the first group and the second group in a similar manner. In one embodiment, the positions 12:00 clockwise to 5:59 are assigned to the first group and the positions 6:00 clockwise to 11:59 are assigned to the second group. When different groups are assigned to different positions around Gantry310, multiple discrete fluence levels can be achieved without substantial degradation of the spatial resolution to which radiation is delivered to Treatment Volume100.

In some embodiments, Leaf Position Calculator450is configured to assign different Leaves210and/or Leaf Pairs230to different groups. For example, every second, third or fourth member of Leaf Pairs230may be assigned to a different group. Using this approach, the first, third, fifth, etc., Leaf Pairs230may be assigned to a first group and the second, fourth, sixth, etc., Leaf Pairs230may be assigned to a second group. The assignment of different Leaf Pairs230may be done in combination with assignment of different positions of Aperture200to different groups. This combination can result in three or four different groups and, thus, up to four different discrete fluence levels.

FIG. 8illustrates an example of Aperture200wherein Leaves210are divided into two groups by assigning alternating member of Leaf Pairs230to a different group. For example, Leaf Pair230C is assigned to a first group and Leaf Pair230D is assigned to a second group. Each if these groups is configured to apply radiation to a different part of Treatment Volume100.FIG. 9Aillustrates the part of Treatment Volume100that would be radiated by the first group andFIG. 9Billustrate the part of Treatment Volume100that would be radiated by the second group. The magnitude of the radiation fluence across the parts of Treatment Volume100illustrated inFIGS. 9A and 9Bmay vary somewhat due to the reduction in spatial resolution that results from the use of alternating Leaf Pair230to control the distribution of radiation in each group. However, approaches to reducing this variation are discussed elsewhere herein.FIG. 9Cillustrates the combined discrete fluence levels achieved using the first group and the second group. A Region910receives a discrete fluence level twice that of other parts of Treatment Volume100because Region910is included in both the first group and the second group.

In practice, Aperture200may include more or fewer Leaf Pairs230than shown inFIGS. 2 and 8. A greater number of Leaf Pairs230per unit area will result in a higher resolution in the distribution of radiation within Treatment Volume100. Thus, the effects of using alternating Leaf Pair230to define parts of Treatment Volume100may partially be compensated for by including a greater number of Leaf Pairs230in Beam Aperture200. Further, the examples illustrated by FIGS.8and9A-9C correspond to one projection of Treatment Volume100to one position of Beam Aperture200around Gantry310. The projection of Treatment Volume100may be different at different positions around Gantry310and the parts of Treatment Volume100to which Leaf Pairs230in the first group and the second group are configured to provide radiation are typically three-dimensional volumes. As such, the relative positions of Leaf Pairs230within Gantry310may change as Beam Aperture200is moved around Gantry310. These changes may partially compensate for the effects of using alternating Leaf Pair230to radiate a part of Treatment Volume100.

In some embodiments, Beam Aperture200is configured to rotate in Directions250as indicated inFIG. 2, e.g. around the direction of propagation of the radiation. This rotation may occur while Beam Aperture200is stopped at one or more positions around Gantry310and/or may occur as Beam Aperture200is moved around Gantry310. Because rotation of Beam Aperture200in Directions250changes which particular members of Leaf Pairs230cover particular parts of Treatment Volume100, rotation of Beam Aperture200may reduce the resolution related effects of using alternating Leaf Pair230to radiate parts of Treatment Volume100.

Leaf Position Calculator450may further be configured for determining how to divide Treatment Volume100into different parts for treatment using different groups of Leaf Pairs230. In some embodiments, each projection of Treatment Volume100is divided using an arbitrary division line. On one side of the division line those parts of Treatment Volume100that are to receive the lowest discrete fluence level are assigned to a first group, and on the other side of the division line those parts of Treatment Volume100that are to receive the lowest discrete fluence level are assigned to a second group.

For example, a Division Line920is shown intersecting Treatment Volume100inFIG. 9C. Those parts of Treatment Volume100that are to receive the lowest discrete fluence level and are to the left of Division Line920are assigned to the first group. Those parts that are to receive the lowest discrete fluence level and are to the right of Division Line920are assigned to the second group. Those parts of Treatment Volume100that are to receive a greater discrete fluence level are assigned to both the first group and the second group. The resulting radiation distributions are illustrated inFIGS. 9A and 9B, respectively.

To clarify the relationship between the radiation distributions illustrated inFIGS. 9A and 9B,FIGS. 9D and 9Eillustrate overlays ofFIG. 8onFIGS. 9A and 9B, respectively.

Division Line920need not be a straight line. For example,FIG. 10Aillustrates the use of a curved Division Line920to separate disjoint parts of Treatment Volume100. The separate disjoint parts of Treatment Volume100are radiated by using Aperture Leaves210to create at least two separate openings in the same aperture at the same time. Further, Treatment Volume100may be divided using a plurality of alternative Division Lines920.FIG. 10Billustrates two alternative Division Lines920that may be used to separate parts of Treatment Volume100. In some embodiments, Division Line920changes as Beam Aperture200moves around Gantry310. Several division lines can be used simultaneously. Further, any two dimensional region within a target can be assigned to a group of leaf pairs.

In some embodiments, each of Division Line920is automatically generated using Leaf Position Calculator450. In some embodiments, Division Line920is manually selected by a user using User Interface480. For example, a user may use User Interface480to manually draw Division Line920on an image of Treatment Volume100.

In some embodiments, Leaf Position Calculator450is configured to calculate positions for each Leaf Pair230at each position around Gantry310. These calculations may include consideration of the mechanical limitations of Beam Aperture200. For example, the speed at which Leaves210can be moved may be limited and it may be undesirable to have to wait for leaf movement as Beam Aperture200is moved around Gantry310. Calculated positions for each Leaf Pair230may, therefore, be automatically reviewed to assure that they can be efficiently implemented using Beam Aperture200. If moving each Leaf Pair230to the calculated positions would significantly slow the treatment process, then Leaf Position Calculator450may automatically modify the calculated positions, or perform new calculations of leaf positions using different Division Lines920and/or rotational orientations of Beam Aperture200.

FIG. 11illustrates methods of providing radiation to a treatment volume, such as Treatment Volume100, according to various embodiment of the invention. In these methods, a plurality of optimal fluences is calculated, a plurality of discrete fluence levels is selected in order to approximate the optimal fluences, leaf positions are calculated, and the calculated leaf positions are optionally used to deliver radiation to a treatment volume.

In a Receive Optimal Fluences Step1110, a plurality of optimal fluences to be delivered to Treatment Volume100is received. These optimal fluences are optionally continuous and have been determined in order to achieve the desired three-dimensional dose distribution in the treatment volume. The characteristics of the desired three-dimensional dose distribution have been specified by a user, e.g., by a medical doctor, by a physicist or by a dosimetrist, based on medical needs. The user may specify that the values of the three-dimensional dose distribution need to be lower, or smaller, near radiation sensitive healthy tissue. The values of the desired three-dimensional dose distribution will typically vary as a function of position within the Treatment Volume100. The Fluence Determination Engine430used the three-dimensional dose distribution to calculate the two-dimensional optimal fluences for each static Gantry310angle.

In a Determine Discrete Fluence Levels Step1120, a plurality of discrete fluences levels is selected to approximately reproduce the, optionally continuous, optimal fluences, received in Receive Optimal Fluences Step1110. The selected discrete fluence levels may be similar to those illustrated by Solid Line560inFIGS. 5A and 5B. In some embodiments, Determine Fluence Levels Step1120is performed automatically using Fluence Determination Engine430. In these embodiments, Processor460is used to calculate two, three, four, or more discrete fluence levels. In some embodiments, Determine Fluence Levels Step1120is performed with input from a user using User Interface480. For example, a user may adjust the discrete fluence levels determined using Fluence Determination Engine430, or the user may determine the discrete fluence levels manually.

In a Calculate Leaf Positions Step1130, positions of Leaves210and/or Leaf Pairs230at each of a plurality of beam aperture positions are calculated. These positions of Leaf Pairs230are calculated to achieve the plurality of discrete fluence levels by moving the beam aperture one or fewer times around an arc of rotation, such as that characterized by Gantry310. For example, in some embodiments the leaf positions are calculated to achieve the plurality of discrete fluence levels by moving the beam aperture once around Gantry310. In some embodiments, the leaf positions are calculated to achieve the plurality of discrete fluence levels by moving the beam aperture part of the way around Gantry310, e.g., from the 12:00 position clockwise to the 11:00 position. Calculate Leaf Positions Step1130optionally includes calculation of how to rotate Aperture200in Directions250as illustrated inFIG. 2.

Calculate Leaf Positions Step1130optionally includes associating a first part of Leaves210with a first discrete fluence level in the beam aperture positions around Gantry310and associating a second part of Leaves210with a second discrete fluence level in the beam aperture positions. When the first group and the second group are related to aperture positions, individual Leaf Pairs230are configured to deliver radiation to the first part of Treatment Volume100at gantry positions associated with the first group and configured to deliver radiation to the second part of the treatment volume at gantry positions associated with the second group. In some embodiments, opposing gantry positions are associated with different groups.

Calculate Leaf Positions Step1130optionally includes assigning a first Leaf Pair230of Beam Aperture200to a first group and assigning a second Leaf Pair230of Beam Aperture200to a second group. The first Leaf Pair230is configured to deliver radiation to the first part of Treatment Volume100and the second leaf pair is configured to deliver radiation to the second part of Treatment Volume100. For example, in some embodiments, alternating Leaf Pairs230may be assigned to the first group and second group respectively. In some embodiments, every third or every fourth Leaf Pair230is assigned to the same group and other Leaf Pairs230are assigned to other groups. Radiation is optionally delivered to both the first part and second part of Treatment Volume100at the same time.

Calculate Leaf Positions Step1130optionally includes both associating beam aperture positions around Gantry310and associating different Leaf Pairs230with different groups. For example, Calculate Leaf Positions Step1130optionally includes dividing Treatment Volume100into first through fourth parts, assigning opposing aperture positions to the first part and second part, and also assigning each leaf pair to either the third or the fourth group. This may result in three or four fluence levels.

Calculate Leaf Positions Step1130optionally includes determining that the calculated leaf positions can be achieved within mechanical limitations of Beam Aperture200. For example, Calculate Leaf Positions Step1130may include a determination of how quickly Leaves210can be moved between the calculated leaf positions.

In a Deliver Radiation Step1140, radiation is delivered at the plurality of fluence levels to Treatment Volume100using the leaf positions calculated in Calculate Leaf Positions Step1130.

Several embodiments are specifically illustrated and/or described herein. However, it will be appreciated that modifications and variations are covered by the above teachings and within the scope of the appended claims without departing from the spirit and intended scope thereof. For example, while many of the illustrations and examples disclosed herein are in a two-dimensional context, one of ordinary skill in the art will understand that these same illustrations and examples are intended to be applied to the three dimensions actually encountered in radiation therapy. Further, various embodiments of the invention include computing instructions configured to perform various methods and functions described herein, and stored on a computer read readable media. Some embodiments of the invention do not include directly controlling a radiation delivery device. For example, the information produced using the methods discussed herein may be used as a starting point for other algorithms, or can be stored for later used. In these embodiments, Leaf Controller440is optional.