WO2011042819A1

WO2011042819A1 - Combination of vmat and standard imrt

Info

Publication number: WO2011042819A1
Application number: PCT/IB2010/054188
Authority: WO
Inventors: Michael Kaus; Karl Bzdusek; Matthias Guckenberger; Anne Richter; Matthieu Bal
Original assignee: Koninklijke Philips Electronics, N.V.
Priority date: 2009-10-06
Filing date: 2010-09-16
Publication date: 2011-04-14

Abstract

To develop a radiotherapy plan for treating a target tissue (15), radiation intensity maps (33) are analyzed to determine dose requirements at various gantry angle positions of a radiation source (16) and a collimator (18) around the target (15). Over arc segments of the angular positions at which intensity modulation and radiation dose are high, the system operates in a step-and-shoot (SAS) mode. In other angular segments, the radiation source and collimator are moved and operated continuously. During continuous movement of the radiation source, at least one of an intensity and a cross-sectional shape of the radiation beam is modulated.

Description

COMBINATION OF VMAT AND STANDARD IMRT

DESCRIPTION

The present application finds particular utility in radiation therapy systems. However, it will be appreciated that the described technique(s) may also find application in other types of radiation delivery systems, other medical imaging systems, and/or other medical applications.

In radiotherapy techniques, a linear accelerator (LINAC) or other radiation source is used for treatment delivery. For intensity modulated radiation therapy (IMRT) dose is typically delivered in either a step-and-shoot mode, sliding-window mode or in a continuously moving arc. Major advantages of treatment with a continuously moving single arc are faster delivery times and reduction of monitor units compared to the step- and-shoot and sliding window mode.

However, in complex radiation therapy planning cases, a single volumetric modulated arc therapy (VMAT) beam may not be sufficient to meet the desired plan objectives or match the plan quality of standard IMRT planning.

VMAT planning with a single arc may be limited in terms of intensity modulation in order to limit multi-leaf collimator leaf (MLC) motion. One of the most limiting factors is the leaf sweep motion that exposes undesirable tissue to radiation when it modulates between MLC segments.

There is an unmet need in the art for systems and methods that facilitate delivering a desired radiation dose to a target tissue with improved accuracy and speed, and the like, thereby overcoming the deficiencies noted above.

In accordance with one aspect, a system that facilitates combined step- and-shoot (SAS) and arc beam radiation delivery includes a radiation source that generates a radiation beam, a collimator that collimates the radiation beam into a collimated radiation beam, and a rotatable gantry upon which the radiation source and the collimator are mounted and rotated in an arc about a target tissue in a volume of interest. The system further includes a processor that executes computer-executable instructions stored in a memory, the instructions including defining first arc segments along which the radiation source moves continuously, defining second arc segments at which the radiation source moves in steps and generates the radiation beam at each step, and selecting collimator patterns to define cross-sectional shapes of the radiation beam.

In accordance with another aspect, a method of performing combined step-and-shoot (SAS) and arc radiation beam delivery to a target tissue includes defining first arc segments along which the radiation source moves continuously, defining second arc segments at which the radiation source moves in steps and generates the radiation beam at each step, and selecting collimator patterns to define cross-sectional shapes of the radiation beam.

In accordance with another aspect, a method of radiation treatment includes moving a radiation source along an arc, and during at least a first segment of the arc, controlling the radiation source to move continuously and generate a radiation beam continuously. The method further includes, during at least a second segment of the arc, controlling the radiation source to move in steps and to generate the radiation beam between steps.

In accordance with another aspect, a method of performing combined sliding window intensity field and arc radiation beam delivery to a target tissue includes defining first arc segments along which the radiation source moves continuously, and defining angular positions around a gantry at which the radiation source is stopped and generates a sliding window intensity field type radiation beam. The method further includes selecting collimator patterns to define cross-sectional shapes of the radiation beam.

In accordance with another aspect, a method of optimizing modulation of an intensity of a radiation beam includes analyzing radiation beam intensity maps generated over a range of angular positions of a radiation source around a gantry to which the radiation source is movably coupled, and assigning scores to the angular positions as a function of geometric qualities of the intensity maps, wherein a higher score indicates a higher degree of intensity modulation. The method further includes assigning weights to the angular positions as a function of dose to be delivered at each angular position, and storing the angular positions with assigned scores and weights in a computer-readable medium.

One advantage is that radiation dose delivery efficiency is improved. Another advantage resides in improved dose delivery speed. Still further advantages of the subject innovation will be appreciated by those of ordinary skill in the art upon reading and understand the following detailed description.

The drawings are only for purposes of illustrating various aspects and are not to be construed as limiting.

FIGURE 1 illustrates a system that facilitates combining step-and-shoot (SAS) radiation beams with arc radiation beams to minimize radiation dose to healthy tissue while efficiently irradiation a target tissue (e.g., a tumor).

FIGURE 2 is an illustration of the multi-leaf collimator (MLC), in accordance with various aspects described herein.

FIGURE 3 illustrates a method for combining SAS and arc radiation beams to improve tumor irradiation speed and efficacy, in accordance with various aspects described herein.

FIGURE 4 illustrates the gantry with a volume of interest positioned therein, and a plurality of arcs punctuated by SAS regions shown around the gantry, such as are employed in conjunction with the systems and methods described with regard to the preceding figures.

FIGURE 1 illustrates a system 10 that facilitates combining step-and- shoot (SAS) radiation beams with continuous arc radiation beams to minimize radiation dose to healthy tissue while efficiently irradiation a target tissue 15 (e.g., a tumor). The system 10 includes a rotatable gantry 12 in which a volume of interest (VOI) 14 (e.g., a patient or portion thereof) is positioned. The VOI includes a target tissue 16 (e.g., a tumor or other tissue) to be irradiated by a radiation source 18. In one embodiment, the radiation source is a linear accelerator (LINAC) radiation source. A multi-leaf collimator (MLC) 18 collimates radiation 20 from the radiation source. Collimated radiation 22 passing through the MLC irradiates the target tissue, while other radiation 20 is blocked by the MLC to mitigate irradiation of healthy tissue surrounding the target. A control processor 24 is coupled to the radiation source and/or the gantry to control radiation emitted from the radiation source, as well as movement or position of the radiation source around the gantry. The processor is coupled to a memory 26 that stores computer-executable instructions for execution by the processor in performing the various methods and actions described herein, as well as other data germane thereto. The processor and memory are additionally coupled to a graphical user interface (GUI) 28 that presents information to a user.

The memory stores one or more VMAT radiation therapy algorithms 30 for generating arc radiation therapy plans, and one or more IMRT radiation therapy algorithms 31 for generating intensity-modulated SAS radiation therapy plans. Image data (e.g., of the patient and/or target tissue therein) is also stored in the memory and optionally displayed on the GUI 28 along with one or more radiation intensity maps 33. In one embodiment, an intensity map(s) showing modulated radiation intensity is overlaid on an image of the target tissue.

In one example method, the processor 24 defines step-and-shoot beams 34 and arc beams 35. The beams 34, 35 can be defined manually (e.g., by a user interacting with or inputting information into the GUI using an input tool (not shown)) or by an automated technique such as geometrical evaluation of a 3D opening density matrix (ODM) 36, or the like.

The processor 24 performs intensity modulation optimization at a predetermined sample of gantry angle positions e.g., every 10°, 15°, 30°, or some other predetermined gantry angle interval around the patient. For instance, the sample rate may be a function of a total number of gantry angle positions (e.g., percentage thereof, such as 20%, 10%, 8%, 5%, etc.). Alternatively, the sample rate may be a function of a predefined interval of gantry angle positions, such as every 5^th position, every 10^th position, every 15^th position, every 17^th position, or some other predetermined interval. After intensity modulation optimization, the processor analyzes the intensity maps 33 (e.g., ODM, fluence maps, etc.) for complexity and assigns scores 37 the gantry angles. A higher score indicates a greater degree of intensity modulation. Additionally, a weight is assigned to each gantry angle as a function of beam-on time (e.g., dose delivered). Furthermore, weights are assigned to the gantry angle positions as a function of geometric qualities of the intensity maps. Angles with the combination of the most intensity modulation (score) and highest weight in terms of beam-on (e.g., duty cycle) time or monitor units are selected as step-and-shoot beam 34 angles (e.g., SAS endpoints). In one embodiment, the score and the weight for each gantry angle are compared to first and second predetermined threshold levels (respectively), and, if greater than their respective threshold levels, the gantry angle is designated as an SAS endpoint. The predetermined threshold levels are set as a function a maximum desired or allowed radiation dose (e.g., 80%, 90%, or some other predefined level).

MLC segments 38 are generated and assigned to either the arc beams 35 or step-and-shoot beams 34 to limit leaf sweep motion in the MLC 18. An MLC segment is a unique orientation of leaves in the MLC, relative to one another, to generate a desired window for a desired beam shape. For instance, segments 38 that have relatively little variation from one gantry angle to the next are included in the VMAT arc beam 35, while segments that have relatively large variation or only exist for limited angles are included in the SAS beams 34. Segments for step-and-shoot beams can also be selected based on the more limited machine constraints of the arc.

The processor 24 concurrently or serially optimizes all arc and SAS segments. Segments assigned to the arc are optionally limited based on machine constraints. The processor 24 causes the radiation source 16 to deliver a sequence of one or more full arcs, divided into multiple arcs with end points at the step-and-shoot positions. In one embodiment, radiation is output as multiple beams with small sub-arcs, in conjunction with SAS beams performed at the end-points of the sub-arcs. That is, the sub-arcs are punctuated and delineated by the SAS beam angle positions around the gantry.

In this manner, the control processor 24 moves the radiation source 16 in a continuous arc, interrupted by one or more step-and-shoot segments or positions. The intensity of the delivered dose can also be modified or modulated as the radiation source traverses one or more arcs. In an alternate embodiment, a sliding window intensity field is used instead of one or more of the step-and-shoot segments. In another embodiment, the sliding window is employed with a continuous, very slow gantry motion which can be defined as a single arc with variable gantry spacing in the control points. By adding several step-and-shoot beams to the VMAT arcs at optimal beam angles, plan quality similar to IMRT plans is achieved, where the IMRT plans have significantly more beams and longer delivery times. Additionally, the system 10 limits leaf sweep motion in the MLC 18. MLC segments 34 that have relatively little variation from one gantry angle to the next are included in the VMAT arc 37. Segments that have relatively large variation or only exist for limited angles are included in the step-and- shoot beams 36 and thus avoid the leaf sweep motion.

As mentioned above, the system includes the processor 24 that executes, and the memory 26 that stores, computer executable instructions for carrying out the various functions and/or methods described herein. The memory 26 may be a computer- readable medium on which a control program is stored, such as a disk, hard drive, or the like. Common forms of computer-readable media include, for example, floppy disks, flexible disks, hard disks, magnetic tape, or any other magnetic storage medium, CD- ROM, DVD, or any other optical medium, RAM, ROM, PROM, EPROM, FLASH- EPROM, variants thereof, other memory chip or cartridge, or any other tangible medium from which the processor 24 can read and execute. In this context, the system 10 may be implemented on or as one or more general purpose computers, special purpose computer(s), a programmed microprocessor or microcontroller and peripheral integrated circuit elements, an ASIC or other integrated circuit, a digital signal processor, a hardwired electronic or logic circuit such as a discrete element circuit, a programmable logic device such as a PLD, PLA, FPGA, Graphical card CPU (GPU), or PAL, or the like.

FIGURE 2 is an illustration of the multi-leaf collimator (MLC) 18, in accordance with various aspects described herein. The MLC includes a plurality of slidable collimator leaves 40 that slide laterally (relative to the plane of the page of Figure 2) to collimate radiation emitted by the radiation source (Fig. 1) to ensure that the target tissue 15 is sufficiently irradiated while nearby healthy tissue is protected. It will be understood that as the radiation source and MLC 18 move around the gantry on which they are mounted, the cross-section presented by the target 15 changes. That is, at different gantry angles (e.g., perspective view points), the shape of the target is different. The processor 24 (Fig. 1) adjust the leaves 40 of the MLC so that the radiation beam passed there through consistently irradiates the target tissue only, while preventing radiation from passing to nearby healthy tissue.

FIGURE 3 illustrates a method for combining SAS and arc radiation beams to improve tumor irradiation speed and efficacy, in accordance with various aspects described herein. At 50, a radiation treatment plan (RTP) is developed. The RTP is designed to deliver a pre-selected total higher dose to the target and a lower dose to surrounding tissue, particularly radiation-sensitive tissue. In each session, dose delivered to each tissue is the sum of the dose delivered along each of a plurality of trajectories by defining an arc and step-and-shoot beams. The beams can be defined manually or by an automated technique such as geometrical evaluation or evaluation of a 3D opening density matrix (ODM), or the like. At 52, intensity modulation optimization is performed at a predetermined sample of gantry angle positions around the patient. For instance, the sample rate may be a function of a total number of gantry angle positions (e.g., percentage thereof, such as 20%, 10%, 8%, 5%, etc.). Alternatively, the sample rate may be a function of a predefined interval of gantry angle positions, such as every 5^th position, every 10^th position, every 15ths position, every 17^th position, or some other predetermined interval.

At 54, intensity maps (e.g., ODM, fluence maps, etc.) are analyzed for complexity and scores are assigned. A higher score indicates a greater degree of intensity modulation. Additionally, a weight is assigned to each gantry angle as a function of beam-on time (e.g., dose delivered). At 56, angles with the combination of the most intensity modulation and highest weight in terms of beam-on (e.g., duty cycle) time or monitor units are selected as step-and-shoot beam angles. At 58, MLC segments are generated and assigned to either the arc or step-and-shoot beams to limit leaf sweep motion in the leaf collimator. For instance, segments that have relatively little variation from one gantry angle to the next are included in the VMAT arc, while segments that have relatively large variation or only exist for limited angles would be included in the step and shoot beams. Segments for step-and-shoot beams can also be selected based on the more limited machine constraints of the arc.

At 60, simultaneous optimization of arc segments of the radiation source travel is performed to generate the final RTP. The RTP is optionally reviewed by an oncologist or radiologist to be certain that a sufficiently high dose of radiation is delivered to the target and sufficiently low doses are delivered to the adjacent tissue. At 62, beam delivery is performed. The beam is delivered continuously with at least one of its speed of movement, intensity, and cross-sectional shape modulated during travel along at least a first arc segment. At the end of the first arc segment, the radiation source is operated in the step-and-shoot mode, in which the radiation source stops in one or more angular positions or steps along at least a second arc segment. The radiation beam is turned off during movement between steps, and on at each step position. The beam intensity and cross-section can be the same at each step or can be different at different steps.

FIGURE 4 illustrates the gantry 12 with a volume of interest 14 positioned therein, and a plurality of first arc segments 70 punctuated by second arc segments 72 shown around the gantry, such as are employed in conjunction with the systems and methods described with regard to the preceding figures. Also illustrated are single-shot step and shoot gantry positions 74. Although the gantry is illustrated as a circle for simplicity of illustration, it is to be appreciated that the radiation source may and often does move only along a limited circular segment. Moreover, the radiation source and a counterweight may be mounted on a C-arm that rotates around a central axis such that the radiation source moves along the arc, arc segment, or circle. In addition to the movement of the radiation source, the patient couch may also be dynamically adjusted during radiation or during pauses such as step-and-shoot delivery. This movement can create non-circular or random trajectories. The radiation source (not shown) generates the radiation beam intermittently in the SAS mode in the second arc segments 72, and generates the radiation beam as it moves continuously along the first arc segments 70 between the second arc segments 72. In one embodiment, the radiation beam is continuous along the first arc segment, moving at a fixed or variable speed. In another embodiment, the radiation beam is gated between steps in the step and shoot mode, such that large adjustments can be made to the collimator without exposing the patient to excess radiation. It will be appreciated that although the SAS or second arc segments are shown as evenly spaced along the gantry circumference, they may be positioned at irregular intervals or position as needed to ensure adequate irradiation of the target tissue.

The innovation has been described with reference to several embodiments. Modifications and alterations may occur to others upon reading and understanding the preceding detailed description. It is intended that the innovation be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.

Claims

CLAIMS Having thus described the preferred embodiments, the invention is now claimed to be:

1. A system (10) that facilitates combined step-and-shoot (SAS) or sliding- window and arc beam radiation delivery, including:

a radiation source (16) that generates a radiation beam (20);

a collimator (18) that collimates the radiation beam (20) into a collimated radiation beam (22);

a rotatable gantry (12) upon which the radiation source (16) and the collimator (18) are mounted and rotated in an arc about a target tissue (15) in a volume of interest (14); and a processor (24) that executes computer-executable instructions stored in a memory (26), the instructions including:

defining first arc segments (70) along which the radiation source moves continuously;

defining second arc segments (72) at which the radiation source moves in steps and generates the radiation beam at each step;

selecting collimator patterns to define cross-sectional shapes of the radiation beam.

2. The system according to claim 1, the instructions further including:

modulating an intensity of the radiation beam as the radiation source (16) moves continuously through the first arc segments (70), and in steps along the second arc segments (72).

3. The system according to claim 2, the instructions further including optimizing the modulation of the intensity of the radiation beam, including:

analyzing intensity maps generated over a range of angular positions of the radiation source;

assigning scores to the angular positions, wherein a higher score indicates a higher degree of intensity modulation; assigning weights to the angular positions as a function of dose to be delivered at each angular position; and

assigning scores to the angular positions as a function of geometric qualities.

4. The system according to claim 3, the instructions further including:

defining the second segments (72) based on the angular positions with scores above a first predetermined threshold and weights above a second predetermined threshold. .

5. The system according to any one of claims 1-4, wherein the movement, intensity, and cross-sectional shape of the radiation beam in the first arc segments (70) are controlled using a volumetric modulation arc therapy algorithm (30).

6. The system according to any one of claims 1-5, wherein the movement, intensity, and cross-sectional shape of the radiation beam in the second arc segments (72) are controlled using an intensity modulation radiation therapy algorithm (31).

7. The system according to any one of claims 1-6, wherein the radiation source (16) includes a linear accelerator (LINAC) radiation source.

8. The system according to any one of claims 1-7, the instructions further including:

controlling the collimator (18) to adjust the cross-sectional shape of the radiation beam while the radiation source (16) is moving.

9. The system according to any one of claims 1-8, the instructions further including:

controlling the radiation source (16) and the collimator (18) to deliver the radiation beam as the radiation source and the collimator move continuously along the first arc segments (70) and in steps along the second arc segments (72);

and

controlling the radiation source and the collimator to deliver the radiation beam in one or more shots during the second arc segments (72).

10. A method of performing combined step-and-shoot (SAS) and arc radiation beam delivery to a target tissue (15), including:

defining second arc segments (72) at which the radiation source moves in steps and generates the radiation beam at each step; and

11. The method according to claim 10, further including:

12. The method according to claim 11, further including optimizing the modulation of the intensity of the radiation beam, including:

assigning scores to the angular positions, wherein a higher score indicates a higher degree of intensity modulation;

assigning weights to the angular positions as a function of dose to be delivered at each angular position; and

assigning scores to the angular positions as a function of geometric qualities.

13. The method according to claim 12, further including:

defining the second segments (72) based on the angular positions with scores above a first predetermined threshold and weights above a second predetermined threshold.

14. The method according to any one of claims 10-13, further including: controlling the movement, intensity, and cross-sectional shape of the radiation beam in the first arc segments (70) using a volumetric modulation arc therapy algorithm (30).

15. The method according to any one of claims 10-14, further including:

controlling the movement, intensity, and cross-sectional shape of the radiation beam in the second arc segments (72) using an intensity modulation radiation therapy algorithm (31).

16. The method according to any one of claims 10-15, wherein the radiation source (16) includes a linear accelerator (LINAC) radiation source.

17. The method according to any one of claims 10-16, further including:

and

18. A method of radiation treatment planning, including:

moving a radiation source (16) along an arc;

during at least a first segment (70) of the arc, controlling the radiation source to move continuously and generate a radiation beam continuously; and

during at least a second segment of the arc (72), controlling the radiation source to move in steps and to generate the radiation beam between steps.

19. The method according to claim 18, further including:

modulating at least one of an intensity of the radiation beam and a cross-sectional shape of the radiation beam as the radiation beam moves continuously along the first arc segment (70).

20. The method according to either one of claims 18 or 19, further including: at each step along the second arc segment (72), delivering the radiation beam with a constant cross-sectional shape and intensity, and between at least some steps changing at least one of the cross-sectional shape and intensity of the radiation beam.

21. A method of performing combined sliding window intensity field and arc radiation beam delivery to a target tissue (15), including:

defining arc segments (70) along which a radiation source (16) moves continuously;

defining angular positions around a gantry (12) at which the radiation source is stopped and generates a sliding window intensity field type radiation beam; and

22. The method according to claim 21, wherein the radiation source (16) moves with a very slow, continuous motion, relative to its speed when moving along the arc segments, while moving across the defined angular positions and generating the sliding window intensity field type radiation beam.

23. A method of optimizing modulation of an intensity of a radiation beam, including:

analyzing radiation beam intensity maps (33) generated over a range of angular positions of a radiation source (16) around a gantry (12) to which the radiation source is movably coupled;

assigning scores to the angular positions as a function of geometric qualities of the intensity maps, wherein a higher score indicates a higher degree of intensity modulation; assigning weights to the angular positions as a function of dose to be delivered at each angular position; and

storing the angular positions with assigned scores and weights in a computer- readable medium (26).

24. The method according to claim 23, further including:

delivering the radiation beam to target tissue (15); and

modulating the intensity of the radiation beam as s function of the assigned scores and weights as the radiation source (16) moves continuously through one or more first arc segments (70), and in steps along one or more second arc segments (72).