WO2004105574A2

WO2004105574A2 - Image guided radiation therapy

Info

Publication number: WO2004105574A2
Application number: PCT/US2004/014917
Authority: WO
Inventors: John W. Wong; Di Yan; Lindsay Watt
Original assignee: William Beaumont Hospital
Priority date: 2003-05-21
Filing date: 2004-05-11
Publication date: 2004-12-09
Also published as: WO2004105574A3

Abstract

The present invention provides a process (10) to adapt a radiation therapy plan for treating cancer in a patient. The process includes generating a radiation therapy plan for treating the patient, obtaining one or more reference images of an object in the patient (14, 16, 18, 20, 22), and obtaining a plurality of portal images or volumetric images or both portal and volumetric images (24, 26, 27, 28, 30) of the object in a patient over a time period. The reference images (14, 16, 18, 20, 22) and portal images or volumetric images or both portal and volumetric images (24, 26, 27, 28, 30) are compared and the radiation therapy plan modified based on the comparison.

Description

IMAGE GUIDED RADIATION THERAPY

RELATED APPLICATION

[0001] This application claims the benefit of U.S. Provisional Application No.

60/472,287, filed May 21, 2003, the entire contents of which are incorporated herein by reference.

BACKGROUND

[0002] The present invention generally relates to radiation therapy. More specifically, the invention relates to image guided radiation therapy.

[0003] Radiotherapy involves delivering a prescribed tumorcidal radiation dose to a specific geometrically defined target or target volume. Typically, this treatment is delivered to a patient in one or more therapy sessions (termed fractions). It is not uncommon for a treatment schedule to involve twenty to forty fractions, with five fractions delivered per week. While radiotherapy has proven successful in managing various types and stages of cancer, the potential exists for increased tumor control through increased dose. Unfortunately, delivery of increased^' dose is limited by the presence of adjacent normal structures and the precision of beam delivery. In some sites, the diseased target is directly adjacent to radiosensitive normal structures. For example, in the treatment of prostate cancer, the prostate and rectum are directly adjacent. In this situation, the prostate is the targeted volume and the maximum deliverable dose is limited by the wall of the rectum.

[0004] In order to reduce the dosage encountered by radiosensitive normal structures, the location of the target volume relative to the radiation therapy source must be known precisely in each treatment session in order to accurately deliver a tumorcidal dose while minimizing complications in normal tissues. Traditionally, a radiation therapy treatment plan is formed based on the location and orientation of the lesion and surrounding structures in an initial computerized tomography or magnetic resonance image. However, the location and orientation of the lesion may vary during the course of treatment from that used to form the radiation therapy treatment plan. For example, in each treatment session (interfraction), systematic and/or random variations in patient setup and in the location of the lesion relative to surrounding anatomy can each change the location and orientation of the lesion at the time of treatment compared to that assumed in the radiation therapy treatment plan. Furthermore, the location and orientation of the lesion can vary during a single treatment session (resulting in intrafraction errors) due to normal biological processes, such as breathing, peristalsis, etc.

SUMMARY OF THE INVENTION

[0005] In general, the present invention provides a process to adapt a radiation therapy plan for treating cancer in a patient. In one aspect, the process includes generating a radiation therapy plan for treating the patient, obtaining one or more reference images of an object in the patient, and obtaining a plurality of portal treatment images or volumetric computer tomography images, or both portal and volumetric images of the object in the patient over a time period. The reference images and the portal and/or volumetric images are compared and the radiation therapy plan is modified based on the comparison between the reference images and the portal and/or volumetric images. During the comparison, medical specialist may approve or disapprove a particular portal and/or volumetric image. [0006] For certain patients, the portal and/or volumetric images are obtained on a daily basis. The portal and/or volumetric images may be obtained with cone- beam computerized tomography and evaluated for setup error and organ motion. In certain implementations, the process includes obtaining off-line computerized tomography images that can be evaluated for setup error and organ motion. The process may include imaging radiographic markers to adjust for patient setup and radiation beam targeting during a treatment session. Alternatively, or additionally, the process may include obtaining computerized tomography images to adjust for patient setup and radiation beam targeting during a treatment session. The images can be viewed on displays, associated, for example, with personal computers distributed over a network.

[0007] Further features and advantages of this invention will become readily apparent from the following description, and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] FIG. 1 is a flow diagram showing the processes involved in image- guided radiation therapy in accordance with an embodiment of the invention; [0009] FIGS. 2(a)-(e) are diagrammatic views of several angular orientations of a cone-beam computerized tomography system used in conjunction with the processes of FIG. 1 ;

[0010] FIG. 3 shows a side view of the cone beam computerized tomography system of FIG. 17;

[0011] FIGS. 4(a)-(d) are diagrammatic sketches illustrating the geometry and orientation of the cone beam computerized tomography imaging system of FIG. 2; [0012] FIG. 5 illustrates a comparison between a reference image and a portal image with the processes of FIG. 1 ;

[0013] FIG. 6 illustrates a sequence of images organized by the processes of

FIG. 1; and

[0014] FIG. 7 illustrates a comparison of set-up error correction between conventional radiation therapy and off-line and on-line adaptive radiation therapy in accordance with the invention.

DETAILED DESCRIPTION

[0015] Referring now to the drawings, a process embodying the principles of the present invention is illustrated therein and designated at 10. As its primary components, the process 10 includes a decision making module 12, a electronic portal imaging device (EPID) database 14, a computerized tomography (CT) database 16, a radiation therapy planning (RTP) database 18, a linear accelerator

(LINAC) database 20, and a database 22 for positron emission tomography and magnetic resonance imaging (PET/MRI).

[0016] The decision making module 12 receives information from one or more of the aforementioned databases to dynamical adapt the radiation therapy program for a patient. Specifically, medical personal 23 such as physicians and radiotherapists interface with the decision making module 12 to make decisions regarding the patient's radiation therapy through the use of several image guidance methods. For example, off-line methods include port film review 24, off-line analysis of setup error from a sequence of portal 2D images 26, and off-line analysis of organ motion from a sequence of CT scans 27. On-line methods include the detection of radio-opaque markers 28 or the evaluation of cone-beam computerized tomography images for volumetric intervention 30 to adjust patient setup and beam targeting. [0017] The process 10 allows the treatment personnel 23 to process and evaluate the imaging data and to make the appropriate treatment decision and correction during the treatment of the patient. The process 10 includes a set of image analysis tools implemented, for example, on personal computers, distributed system-wide over a network at the treatment stations, offices, treatment planning area, etc. The process 10 reads images and objects from "image-generating" stations from the radiation therapy plan database 18 and the LINAC database 20 to facilitate analysis and to write directives back to them without creating another database. The process 10, however, is not limited to the use of treatment images. For example, as mentioned above, the system can be integrated with other imaging databases such as the electronic portal imaging device database 14, the computerized tomography (CT) database 16, and the database 22 for PET and MRI. [0018] Radiation treatment delivered with image guidance provided through the process 10 significantly improves accuracy over conventional therapy programs. Without an effective means to integrate the imaging process and the treatment process, as in conventional systems, the very large amount of imaging data produced by image guided treatment methods can easily overwhelm clinical resources. Therefore, the process 10 integrates the imaging data from various sources to achieve effective image guided radiation therapy and to provide the infrastructure to support the various image guidance strategies, such that the radiation therapy plan can be modified to more effectively treat the patient. [0019] In certain implementations, the process 10 is employed in conjunction with a linear accelerator integrated with cone-beam computerized tomography imaging, such as a system 400 illustrated in FIG. 2, which provides treatment to the patient according to a plan associated with the radiation therapy plan database 18 and provides images for the LINAC database 20.

[0020] As illustrated in FIGS. 2(a)-(e) and 3, the system 400 is an embodiment of a linear accelerator cone beam computerized tomography system. The system 400 is a flat panel imager-based kilovoltage cone beam computerized tomography scanner for guiding radiation therapy on a medical linear accelerator. The cone beam computerized tomography system 400 includes an x-ray source, such as x-ray tube 402 and a flat-panel imager 404 mounted on a gantry 406. The x-ray tube 402 generates a beam of x-rays 407 in the form of a cone or pyramid that have an energy ranging from approximately 30 KeV to 150 KeV, preferably approximately 100 KeV. The flat-panel imager 404 employs amorphous silicon detectors. [0021] The system 400 may be retrofitted onto an existing or new radiation therapy system 700 that includes a separate radiation therapy x-ray source, such as a linear source 409, which operates at a power level higher than that of x-ray tube 402 so as to allow for treatment of a target volume in a patient. The linear source 409 generates a beam of x-rays or particles 411 , such as photons or electrons, that have an energy ranging from 4 MeV to 25 MeV. The system 400 may also include an imager that is aligned with the linear source 409 with the patient interposed therebetween. The imager forms projection images of the patient based on the remnants of the beam 411 that passes through the patient. Note that the x-ray sources 402 and 409 may be separate and contained within the same structure or be combined into a single source that can generate x-rays of different energies. [0022] As shown in FIGS. 2(a)-(e) and 3, the flat-panel imager 404 can be mounted to the face of a flat, circular, rotatable drum 408 of the gantry 406 of a medical linear accelerator 409, where the x-ray beam 407 produced by the x-ray tube 402 is approximately orthogonal to the treatment beam 411 produced by the radiation therapy source 409. Attachment of the flat plane imager 404 is accomplished by an imager support system 413 that includes three 1 m long arms 410, 412 and 415 that form a tripod. Side arms 410 and 415 are identical to one another in shape and have ends attached to a Ax95 Guy pivot 417 which in turn is attached to a mounting 414 by screws that are threaded through aligned threaded holes of the pivot 417 and threaded holes 425 and 431 of plates 433 and 435, respectively, as shown in FIG. 3. As shown in FIGS. 2(b) and 3, the mountings 414 for the arms 410 and 415 are aligned with one another along a line segment 419 that is contained within a plane 421 that is parallel to and offset by approximately 30 cm from the plane containing the flat-plane imager 404. The mountings 414 are separated from one another by approximately 70 cm and are symmetrically positioned with respect to a plane bisecting an imager mount 423 that is attached to the drum 408 270° from the radiation therapy source 409.

[0023] As shown in FIGS. 2(d) and 2(e), there are two preset positions of the flat panel imager 404 relative to the plate 424. As shown in FIG. 2(d), the flat panel imager 404 is centered about the ends of the arm 412. In order to provide a larger field of view, an offset flat panel imager 404 can be used as shown in FIG. 2(e) where the imager 404 is attached to a side of the plate 424 via bolts. Note that it is possible to use a motorized system to move the flat panel imager 404 relative to the plate 424 to provide an easy way to vary the field of view of a cone beam computerized tomography system. This arrangement can be mounted to a robotic arm that is retractable.

[0024] A center arm 412 is also attached to the drum 408 and the flat-panel imager 404. The center arm 412 has one end attached to Ax95 Guy pivot 427 that is in turn attached to a tapped, triangular-shaped, reinforcing plate 426 formed on the drum 408 as shown in FIGS. 2(b) and 3. The plate 426 is approximately 433.8 mm from the rotational axis 428 that intersects the iso-center 430 of the imaging system 400. A second end of the center arm 412 is attached to the plate 424 via a Cx95A right angle joint 425.

[0025] Note that the x-ray tube 402 can also be retrofitted onto an existing stand-alone treatment device so as to be positioned opposite to the flat panel imager 404. As shown in FIGS. 2(a)-(e), the x-ray tube 402 is attached to tube support 440 that is composed of a pair of front and rear faces 442 and 444 and a pair of side faces 446. A multi-leaf collimator 448 is supported within the interior of the tube support 440. The front and rear faces 442 and 444 each include three openings 450, 452 that are aligned with one another and receive one, two, or three cylindrical support arms 454 that are attached to a bearing housing 456 that is bolted to the drum 408. The tube support 440 and the x-ray tube 402 are able to slide along the support arms 454. Note that a cable support 458 spans between the tube support 440 and the bearing housing 456 and contains the wiring necessary to operate the x- ray tube 402. [0026] Turning now to the operation of the system 400, in the description to follow, the term "shape" of the radiation therapy beam 411 is understood to refer to the spatial distribution of the beam in a plane perpendicular to the direction of the beam or to the frequency modulation of the beam after being transmitted through some beam-limiting device. The term "planning image" refers to an image of the patient acquired by volumetric computerized tomography with the system 400 prior to treatment delivery for radiation therapy treatment planning. Such images can be stored in the LINAC database 20 (FIG. 1). The term "constrained plan set" refers to a plurality of radiation therapy treatment plans for a given patient, where each radiation therapy treatment plan is calculated assuming some perturbation of lesion location and/or orientation compared to that in the planning image. For example, a constrained plan set could be calculated where each plan corresponds to a different magnitude of lesion rotation about the x, y and/or z axes.

[0027] The x-ray tube 402 and the flat panel imager 404, arranged in any one of the geometries illustrated in FIGS. 4(a)-(d), are capable of forming 3-D images of the patient on the treatment table in the treatment position. The x-ray tube 402 may be operated so as to produce a pulsed or continuous beam of x-rays 407. The flat panel imager 404 includes an active matrix of imaging pixels incorporating mechanisms for: 1.) converting incident x-rays to electronic charge (e.g., a scintillator in combination with optically sensitive elements at each pixel, or a photoconductor); 2.) integrating and storing the electronic charge at each pixel (e.g., the capacitance of photodiode(s), capacitors, etc. located at each pixel); and 3.) reading the electronic charge out of the device (e.g., a thin-film transistor switch or the like at each pixel, with associated switching control lines and readout lines). The x-ray tube 402 and the flat panel imager 404 preferably move in a circular orbit (or variation thereof) about the longitudinal axis of the patient. Depending on which ones of the imager support systems used, the imager support system accommodates offsets in the x and/or z directions as illustrated in FIG. 4(b). Note that the combined motion of the x-ray tube 402 and/or the flat panel imager 404 in x, y, and/or z is termed the orbit, and may be circular about the patient, or non-circular, e.g., comprising of some combination of linear, sinusoidal, circular, and/or random paths. For example, in the case where the source 402 and imager 404 move independently with respect to one another, the source 402 can move on a sinusoidal or sawtooth path constrained to the surface of a cylinder while the imager 404 moves in a circular path on the surface of a cylinder. In this scenario, the collimator adjusts in real time the shape of the radiation field so it is confined to the imager 404 despite the allowed independent motion of the source 402 and imager 404.

[0028] Cone beam computerized tomography image acquisition involves acquisition of a plurality of 2-D images, where each image preferably corresponds to a different orientation of the x-ray beam 407 and the flat panel imager 404 with respect to the patient 441 , e.g., where the x-ray tube 402 and the flat panel imager 404 traverse a circular or non-circular path about the patient 441 as illustrated in FIG. 4(d). Note that the cone beam computerized tomography image is preferably acquired with the patient on the treatment table, in the treatment position, and immediately prior to treatment delivery. The processes involved in the use of the system 400 are divided conceptually into a variety of off-line and on-line processes, and mechanisms for 2-D image acquisition and 3-D image reconstruction. [0029] In the interim between the 2-D image acquisition and correction of lesion localization errors, the patient 441 is preferably monitored by periodic radiographs obtained with the flat panel imager at one or more gantry angles. In the system 400, these monitor radiographs are analyzed (e.g., by calculation of difference images) in order to provide a check against intrafraction motion of the patient 441.

[0030] The process 10 in conjunction with the system 400 entail a streamlined process for rapid lesion localization, selection of an appropriate RTP, dosimetry review, and transfer of the prescription to the radiation therapy delivery system. The off-line treatment process begins with a planning image (see, e.g., image 500 in FIG. 6) on which contours of the target volume and surrounding structures are defined, and margins for target deformation, delivery precision, and delineation precision are applied. Inverse planning is performed according to a given protocol for radiation therapy of the given treatment site, e.g., a number of radiation therapy beams 411 directed at the patient 441 from various angles, with target dose uniformity and normal tissue volume constraints to match the prescription.

[0031] For on-line plan selection and correction of lesion localization errors, the target volume/lesion 444 and its relationship to bony structure in the planning image are prepared for use as priors, for example, for the on-line volumetric intervention 30 (FIG. 1), and the constrained plan set is transferred to the radiation therapy system to verify deliverability prior to the on-line procedure. In the on-line treatment process, the patient 441 is set up on the treatment table 443 in the treatment position, and cone beam computerized tomography images are acquired as described above. The target volume/lesion 444 and surrounding structures are delineated in the cone beam computerized tomography data, thereby identifying the translations and/or rotations of the target volume/lesion 444 relative to the position and orientation in the planning image. The translation of the lesion 444 observed in the cone beam computerized tomography image relative to the planning image is corrected by translation of the patient 441 on the treatment table 443 in the y and/or z directions, and/or by rotation about the x axis. The orientation of the lesion 444 (i.e., rotations about the y and/or z axes) are corrected by selecting from the previously calculated constrained plan set a modified RTP that most closely corresponds to the measured rotation of the lesion 444. Meanwhile, radiographic monitoring of the patient 441 can be used to check against intrafraction motion of the patient 441. Furthermore, a cone beam computerized tomography image acquired immediately prior to, during, or following the treatment procedure can be obtained in order to provide accurate representation of the location of patient anatomy during treatment delivery, which can be stored for off-line review, evaluation, and modification of subsequent treatment sessions. Following transferal of the prescription to the delivery system, the treatment plan is executed according to the patient setup and treatment plan determined from the cone beam computerized tomography image.

[0032] Other details of the system 400 and its operation may be found in U.S.

Patent Application No. 09/788,335, filed February 16, 2001 , published as U.S. Patent Publication No. 2003/0007601, the entire contents of which are incorporated herein by reference.

[0033] The organization of the process 10 centers on an image calendar, such as the sequence of volumetric or portal images 510 over a number of days (or weeks, months, or years) shown in FIG. 6, that can be scrolled, for example, with the buttons 512, to relate intuitively to the course of fractionated treatments over a time period as the medical personal interfaces with the decision making module 12. For each treatment fraction, radiographic or volumetric images are arranged as stacks and can be selected for detailed review.

[0034] At the basic level, the process 10 supports "view-boxes" for efficient weekly and chart round. Advanced adaptive radiation therapy tools are also invoked from the image calendar. For off-line treatment intervention, sequential daily portal images 24 or CT images 27 are analyzed for systematic and random setup error and organ motion 26. The results are then sent to the treatment planning system 18 where planning target volume (PTV) margins are re-optimized for the individual patient.

[0035] For on-line intervention, image guidance tools are invoked at the treatment machine by trained radiotherapists. Radiopaque markers 28, for example, in breast or prostate treatments, are localized manually or automatically on a pair of pre-treatment projection images in reference to a pre-loaded pair of corresponding prescription images. For CT guided treatment 30 while the patient is on the couch, the process 10 extends the functionality of 3D virtual simulation to facilitate paired comparison of the pretreatment CT with reference treatment planning CT. Fast 3D image fusion and navigation tools are used to align prescription PTV contours and to evaluate beams-eye views (BEV) trajectories.

[0036] For on-line interventions with either markers 28 or CT images 30, the necessary shifts and rotations are displayed for immediate action. The prescribed and implemented corrections are then recorded in the databases of the LINAC 20, and treatment planning system 18 for plan recalculation purposes. [0037] Accordingly, the process 10 provides for improvements in correcting for random and system setup errors over conventional radiation therapy systems, as indicated in FIG. 8. The left-most schematic of FIG. 8 depicts clusters of image data for conventional radiation therapy (obtained, for example, through the use of markers) relative to an origin, where the set-up error is considered zero. Each cluster of image data 600a, 600b, 600c, 600d is associated with a particular patient. Thus, for conventional radiation therapy, the radiation therapy device is adjusted to cover the setup error for all these patients. The process 10, however, can use offline treatment intervention, as described above, to center the cluster of a particular patient, for example, the cluster 600d, to the origin of the axes such that the therapy device targets a smaller area than that for conventional radiation therapy, as indicated by a comparison between the center schematic and the left-most schematic. Moreover, as depicted in the right-most schematic, the process 10 can use on-line intervention to correct for setup error associated for each image to further reduce the target area of the therapy device.

[0038] With the process 10 supporting electronic portal imaging 14 and CT imaging 16 and review 24, films and paper images are eliminated for the task of weekly portal review and chart round. For example, as shown in FIG. 6, a physician may compare a reference or planning image 500 with a treatment portal image 502 or a CT volumetric image and then either accept or reject the portal or CT image for the image calendar. The improvement in efficiency is significant. For a system 400 that treats 40 patients a day, there can be a savings of >6 hours of a radiotherapist's time per week. Treatment slots can increase by 3 hours. A physician with 20 patients on treatment may save >2 hours per week. The benefits of convenience are intangible. For off-line treatment interventions, images are analyzed independently of the treatment planning systems, increasing their availability for complex planning. When off-line corrections are made by modifying the multileaf collimator (MLC), a standard treatment fraction can be performed within a ^'10 min slot instead of the conventional 15 min slot, thus improving both quality and efficiency. On-line interventions with the process 10 emphasize efficiency in order to minimize deterioration of the imaging information due to patient movement. Both marker and CT guided corrections, 28 and 30, respectively, can achieve better than 2 mm accuracy within a 10 min treatment slot. Since different clinical objectives require different interventional treatment strategies, the process 10 provides effective infrastructure to support decision making, advanced imaged guided treatment, which will not only improve treatment quality, but also treatment efficiency. In conventional therapy systems, once the therapy plan is established, modifications to the plan are not implemented during the course of treatment. The process 10, however, provides feedback to the physician such that the initial radiation therapy plan can be adaptively modified both during treatment sessions and between sessions tto optimize the treatment of the patient.

[0039] As a person skilled in the art will readily appreciate, the above description is meant as an illustration of implementation of the principles of this invention. This description is not intended to limit the scope or application of this invention in that the invention is^' susceptible to modification, variation and change, without departing from spirit of this invention, as defined in the following claims.

Claims

CLAIMSWhat is claimed is:

1. A method of radiation therapy for treating cancer in a patient, comprising: generating a radiation therapy plan for treating the patient; obtaining one or more reference images of an object in the patient; obtaining a plurality of portal images or volumetric images or both portal and volumetric images of the object in the patient over a time period; comparing the reference images with the portal images or volumetric images or both portal and volumetric images; and modifying the radiation therapy plan based on the comparison between the reference images and the portal images or volumetric images or both portal and volumetric images.

2. The method of claim 1 wherein the comparing includes approving or disapproving one or more portal images or volumetric images or both portal and volumetric images.

3. The method of claim 1 wherein the portal images or volumetric images or both portal and volumetric images are evaluated for setup error and organ motion.

4. The method of claim 1 further comprising obtaining off-line, portal or computerized tomography images or both portal and computerized tomography images.

5. The method of claim 4 wherein the off-line images are evaluated for setup error and organ motion.

6. The method of claim 1 further comprising imaging radiographic markers to adjust for patient setup and radiation beam targeting during a treatment session.

7. The method of claim 1 further comprising obtaining computerized tomography images to adjust for patient setup and radiation beam targeting during a treatment session.

8. The method of claim 1 wherein the modifying includes evaluating images from an electronic portal imaging device.

9. The method of claim 1 wherein the modifying includes evaluating images from a positron emission tomography device.

10. The method of claim 1 wherein the modifying includes evaluating images from a magnetic resonance imaging device.

11. The method of claim 1 wherein the portal images or volumetric images or both portal and volumetric images are obtained on a daily basis over the time period.

12. The method of claim 1 wherein the comparing includes viewing the images on a display.

13. The method of claim 12 wherein the viewing includes viewing the images over a plurality of displays distributed over a network.