WO2014022480A1

WO2014022480A1 - Deformable dosimetric phantom

Info

Publication number: WO2014022480A1
Application number: PCT/US2013/052871
Authority: WO
Inventors: Hualiang ZHONG; Teamour NURUSHEV; Indrin CHETTY; Benjamin MOVSAS
Original assignee: Henry Ford Health System
Priority date: 2012-07-31
Filing date: 2013-07-31
Publication date: 2014-02-06

Abstract

In at least one embodiment, a phantom system is provided for measuring radiation dosage. The phantom may include a deformable material including a plurality of landmarks, a plurality of radiation sensors disposed within the deformable material, and at least one artificial tumor including a radiation detector disposed within the deformable material. An actuator may be configured to deform the deformable material and a radiation source may be provided for irradiating the deformable material. Location data from the plurality of landmarks and radiation data from the plurality of radiation sensors and the at least one artificial tumor may be received by a processor, and the location data and the radiation data may have been recorded while the deformable material was being deformed and irradiated. In another embodiment, the phantom may be used to generate and verify simulated dosages, which may be compared to measured dosages.

Description

DEFORMABLE DOSIMETRIC PHANTOM

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. provisional application Serial No.

61/677,637 filed July 31, 2012, the disclosure of which is hereby incorporated in its entirety by reference herein.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0002] The invention was made with Government support under Contract No. NIH/NCI

R01CA140341. The Government has certain rights to the invention.

TECHNICAL FIELD

[0003] One or more embodiments relate to a phantom for assisting in radiotherapy.

BACKGROUND

[0004] Inter and intra-fraction changes in patient anatomy pose a challenge to radiotherapy when delivering a highly conformal dose distribution. When changes in tumor size or breathing patterns are significant, for example in the case of lung or abdominal cancers, large uncertainties may be introduced to the dose calculated for target and organ-at-risk structures. These applications may benefit from the use of adaptive radiotherapy (ART). Deformable image registration (DIR) and dose accumulation are fundamental to ART, yet it is difficult to quantify errors introduced during the process.

SUMMARY

[0005] In at least one embodiment, a phantom system for measuring radiation dosage is provided. The system may include a deformable material including a plurality of landmarks, a plurality of radiation sensors disposed within the deformable material, and at least one artificial tumor including a radiation detector disposed within the deformable material. An actuator may be configured to deform the deformable material and a radiation source may be provided for irradiating the deformable material. A processor is provided and is configured to receive at least location data from the plurality of landmarks and radiation data from the plurality of radiation sensors and the at least one artificial tumor. At least a portion of the location and radiation data may be recorded while the deformable material is being deformed and irradiated.

[0006] In another embodiment, the deformable material is formed of a heterogeneous porous material. The deformable material may be formed of a plurality of adjacent slabs and at least some of the plurality of radiation sensors may be located at interfaces between the slabs. In another embodiment, at least one artificial tumor is located in each slab. Each slab may be formed of the same material and a portion of the slabs may be formed of a heterogeneous sponge material and a portion of the slabs may be formed of polyvinyl alcohol Cryogel (PVA-C).

[0007] In another embodiment, the actuator includes a motor and a piston, the motor being configured to oscillate the piston to axially deform the deformable material. The piston may have an end portion having a spherical or semi-spherical shape, the end portion contacting the deformable material. In another embodiment, the system may further include a flexible bladder in contact with the deformable material and configured to receive a fluid and deform the deformable material. The plurality of radiation sensors may include thermoluminescent detectors (TLDs) and the radiation detector may include a radiation-sensitive film.

[0008] In at least one embodiment, a method of measuring radiation in a deforming phantom is provided. The method may include deforming a phantom formed of a heterogeneous porous material and including a plurality of landmarks, a plurality of radiation sensors, and at least one artificial tumor including a radiation detector. The method may further include irradiating the phantom using a radiation source while the phantom is being deformed, tracking a location of the plurality of landmarks while the phantom is being deformed, and measuring a dosage of radiation in the radiation sensors and the at least one artificial tumor while the phantom is being deformed.

[0009] In another embodiment, the deforming step may include deforming the phantom in an axial direction. The deforming step may also include deforming the phantom with a pressurized fluid. In another embodiment, the tracking step is performed with a four-dimensional (4D) computed tomography (CT) scanner. The deforming step may include deforming the phantom to simulate lung deformation during breathing. The deforming, irradiating, tracking, and measuring steps may be repeated for a plurality of radiation treatments and deformation patterns.

[0010] In at least one embodiment, a method of verifying a simulated radiation dosage using a deformable phantom including a plurality of landmarks and a plurality of radiation sensors is provided. The method may include scanning the phantom while implementing a plurality of deformation patterns to generate and track location data for the plurality of landmarks. A displacement vector field (DVF) of the phantom may be generated using the tracked location data and a radiation dosage in the phantom may be measured during a selected radiation treatment and deformation pattern using the plurality of radiation sensors. The method may further include calculating a simulated radiation dosage based on the DVF for the selected radiation treatment and deformation pattern and verifying the simulated radiation dosage by comparing it to the measured radiation dosage.

[0011] In another embodiment, the method may further include generating an FEM model of the phantom based on the tracked location data and using the FEM model to generate the DVF. If the simulated radiation dosage is different from the measured radiation dosage by more than a predetermined amount, parameters of the simulated radiation dosage may be adjusted and the calculating and verifying steps may be repeated.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] FIGURE 1 is a schematic representation of a cubic phantom including three slabs with diodes embedded on the top of each slab according to an embodiment

[0013] FIGURE 2 is an MIP CT scan of a deformable phantom constructed from heterogeneous sponges with an artificial tumor embedded therein, according to an embodiment;

[0014] FIGURE 3 is a CT intensity histogram of the heterogeneous sponges according to an embodiment; [0015] FIGURE 4 is a photograph depicting thermoluminescent detectors and films embedded in the phantom according to an embodiment;

[0016] FIGURE 5 is an illustration of a rubber-like tumor arranged to be embedded in each slab according to an embodiment;

[0017] FIGURE 6 is an image of the piston motion with respect to the phantom according to an embodiment;

[0018] FIGURE 7 is a phantom system having a cylindrical phantom surrounded by a flexible bladder according to an embodiment;

[0019] FIGURE 8 is an algorithm for generating and verifying a DVF for a phantom according to an embodiment;

[0020] FIGURE 9 is an algorithm for calculating and verifying simulated radiation dosages in a phantom according to an embodiment;

[0021] FIGURE 10 is an algorithm for comparing computed dose distributions to measured distributions according to an embodiment;

[0022] FIGURE 11 is an exemplary FEM algorithm according to an embodiment;

[0023] FIGURE 12 is a graph of four DIR registrations from end-exhale to end-inhale;

[0024] FIGURE 13 is a graph of four DIR registrations from end-inhale to end-exhale;

[0025] FIGURE 14 depicts the consistence error between the registrations of FIGS. 12 and 13;

[0026] FIGURE 15 illustrates a user interface which may be used for dose calculation;

[0027] FIGURE 16 illustrates a linear dose mapping method of dose reconstruction;

[0028] FIGURE 17 illustrates an energy-mass congruence mapping method of dose reconstruction; [0029] FIGURE 18 is a graph of dose warped by EMCM with different DVFs;

[0030] FIGURE 19 is a graph illustrating the results of dose reconstruction; and

[0031] FIGURE 20 is a graph of dose warped by EMCM and linear interpolation.

DETAILED DESCRIPTION

[0032] As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention that may be embodied in various and alternative forms. The figures are not necessarily to scale; some features may be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention.

[0033] In at least one embodiment, a deformable dosimetry phantom 10 is provided. The phantom 10 may be used to measure dose during radiation delivery. The phantom 10 may be used as a tool to verify the total dose calculated by adaptive treatment plans. The phantom 10 may also provide a benchmark for verification of adaptive radiation treatment planning. A goal of adaptive treatment planning is to determine the actual dose delivered to patients during treatment, and thereby to tailor the radiation treatment plan on a daily basis to better conform to the tumor and avoid healthy tissues. In doing so, the outcomes for patients may be improved, either by reducing normal tissue complications for the same target dose, or by escalating the tumor dose for the same level of healthy tissue damage.

[0034] In one embodiment, the phantom 10 helps ensure that each patient's treatment plan is properly adapted to account for inter- and intra-fractional dose errors introduced by organ deformation. While deformable image registration techniques (DIR) can help reduce treatment margins and minimize radiation damage to surrounding healthy tissues, DIR accuracy at the level required for ART in the clinic remains a significant concern. One or more of the deformable lung phantoms described herein may be used to verify the accuracy of dose mapping and accumulation of 4D dosimetry algorithms. [0035] With reference to Figures 1, 2, 4, 6, and 7, a deformable dosimetry phantom 10 is shown. The phantom 10 may represent any suitable organ or body part, such as a lung or prostate, or it may represent a region of the body, such as the abdomen. In at least one embodiment, the phantom 10 is formed of a deformable material 12. The deformable material 12 may be a heterogeneous and/or porous material. In another embodiment, the phantom 10 is formed of a heterogeneous sponge material 14. The heterogeneous sponge material 14 may be a natural sponge or a synthetic sponge. The phantom 10 may include a plurality of deformable slabs 16, for example, a plurality of deformable heterogeneous sponges 14. The phantom 10 may also include a tissue- equivalent tumor 18. In one embodiment, the tissue-equivalent tumor 18 is composed of bolus slabs, however other suitable materials may be used.

[0036] The phantom 10 may have any suitable shape, including the shape of the organ or body region that it is representing. The phantom 10 may also have a uniform shape or cross-section, such as rectangular (as shown in Fig. 1), cubic, cylindrical (as shown in Figs. 2, 4, 6, and 7), egg- shaped, oval, or others. In one embodiment, the phantom 10 includes a plurality of deformable slabs 16, for example, two, three, four, or more slabs. In one embodiment, the slabs 16 each have the same dimensions; however in other embodiments the slabs may be different sizes and/or have different thicknesses. The slabs may each be formed of the same material, such as heterogeneous sponge 14, or one or more slabs may have different compositions. The sponge may be made of naturally heterogeneous material. An example of a histogram of the density of a suitable sponge material is shown in Figure 3. In one embodiment, the sponge material has a density of approximately 0.05 to 0.5 g/cm . In another embodiment, the sponge material has a density of approximately 0.1 to 0.4 g/cm . In another embodiment, the sponge material has a density of approximately 0.1 to 0.3 g/cm . In another embodiment, the sponge material has a density of approximately 0.2 g/cm . The heterogeneity of the sponge may make the phantom 10 appropriate for deformable image registration. The slabs 16 may be bound together to prevent slippage during the deforming process. In one non- limiting example, the phantom 10 may be generally cubic and have a dimension of 20x20x20 cm , and may include four deformable slabs 16, each composed of a heterogeneous sponge with dimension 5x20x20cm .

[0037] In another embodiment, a portion of the slabs 16 may be made of one material and another portion may be made of another material. For example, outer slabs 20 may be provided having a different composition than inner slabs 22. The outer slabs 20 and inner slabs 22 may have the same dimensions or they may have different dimensions (e.g., different thicknesses). In one embodiment, the inner slab or slabs 22 may be formed of a heterogeneous porous material (e.g., sponge material) and the outer slabs 20 may be formed of a porous polymer. In one embodiment, the outer slabs 20 are formed of polyvinyl alcohol Cryogel (PVA-C). The density of the PVA-C may be approximately 1.0 g/cm and the sponge material may have a density of approximately 0.28 g/cm . In one non- limiting example, a phantom 10 is provided having outer slabs 20 of PVA-C with dimensions of 5x20x20cm and a middle slab or slabs 22 composed of a heterogeneous sponge material 14 with dimensions 10x20x20cm .

[0038] In addition to the phantom 10 material itself (e.g., heterogeneous sponge), a plurality artificial landmarks 24, sensors 26, and/or detectors 28 may be included in the phantom 10 to facilitate benchmarking of a deformable image registration algorithm. To measure the accumulated radiation dose, one or more diodes 30, thermoluminescent detectors (TLD) 32, and/or radiation- sensitive films (e.g., gafchromic films) 34 or other sensors/detectors may be disposed within the phantom 10 (as shown in Fig. 4). In at least one embodiment, sensors/detectors 26, 28 are placed at the interfaces 36 between different slabs 16 (as shown in Fig. 1). In addition, visible landmarks 24 may be embedded within or on the external surfaces of the phantom 10. The sensors 26 and landmarks 24 disposed in or on the phantom 10 may be placed at regular intervals throughout the phantom 10 to form a three dimensional grid.

[0039] In addition to landmarks 24, sensors 26, and/or detectors 28 disposed within the phantom 10, artificial tumors 18 may be embedded in the phantom 10, an example of which is shown in Figure 5. In embodiments where the phantom 10 includes multiple slabs 16, artificial tumors 18 may be placed in one or more slabs 16 or in each slab 16. The artificial tumors 18 may include artificial landmarks 24, sensors 26, and/or detectors 28 such as those described above in the phantom 10 material. In one embodiment, the artificial tumors 18 include a radiation-sensitive film

34, which may be a gafchromic film. However, any suitable radiation-detecting device may be included in the artificial tumor 18. The artificial tumor(s) 18 may have any suitable shape to represent a tumor. Non-limiting examples of artificial tumor shapes include spherical, egg-shaped, cubic, rectangular, cylindrical, irregular, and others. As shown in Figure 5, the artificial tumor 18 may be formed of two or more parts or halves 38 that interlock or connect. The radiation-detecting device may be located within the parts or halves 38, and may be disposed in a cut-out or other locating feature 40, such as a notch, depression, or others. The radiation detecting device may also be held in place by an adhesive or any other known method of fixation.

[0040] The phantom 10 may include multiple detectors, for example, film for measuring tumor dose and TLD for lung dose. These multiple embedded landmarks are visible in 4D CT images. Dose detectors 26, 28 (e.g., diodes and TLD) may be configured at the interfaces 36 between slabs 16 and films 34 may be configured within artificial tumor(s) 18, providing convenient dose readout and processing for validation of dose accumulation. Artificial tumors 18 may be embedded at different locations in each slab 16. The tumor 18 may be uniquely designed to hold a radio-sensitive film 34 so that measured data can be correctly compared with computational results. The overall deformation of the phantom 10 may be quantified by a finite element method.

[0041] With reference to Figure 1, 6, and 7, the phantom 10 may be deformed in one, two, or three dimensions. Deformation may include applying a compressive force or a tensile force. In one embodiment, the phantom 10 is deformed in one dimension, for example, along one axis of the phantom 10 (as shown in Fig. 1). For a rectangular phantom 10, this may include deforming the phantom 10 perpendicular to one face of the phantom 10. If the phantom 10 is cylindrical, the phantom 10 may be deformed perpendicular to the end faces. In another embodiment, the phantom 10 is deformed in two dimensions, for example, along two different axes of the phantom 10. For a rectangular phantom 10, this may include deforming the phantom 10 in two perpendicular directions. In another embodiment, the phantom 10 is deformed in three dimensions. For a rectangular phantom 10, this may include deforming in a direction perpendicular to each face. For a cylindrical phantom 10, the three dimensional deformation may include applying an axial force to the end faces and a distributed force along the curved face (as shown in Fig. 7), for example, a hydrostatic force or pressure. For axial deformation, a rod or piston 42 may be used to impart a force on one side or face of the phantom 10. The rod 42 may have an end portion 44, or a piece that connects to the rod, that contacts the phantom 10, which may have a shape different than the rod 42. Non-limiting examples of the shape of the end portion 44 or end piece include spherical, semi-spherical (as shown in Figs. 2 and 6), rectangular, conical, rectangular prism, flat or plate-like, or others. [0042] In one embodiment, the phantom 10 is a lung phantom 10 which is compressed by a piston 42 to simulate the diaphragm motion. The piston may have an end portion 44 or end piece that has a spherical or semi-spherical shape in order to simulate the diaphragm. In another embodiment, the phantom 10 material (e.g., heterogeneous sponge) may be enclosed (partially or fully) in a surrounding material 46, such as one or more flexible bladders 48, and then compressed using fluid 50 (e.g., water or air) to simulate a motion of the representative organ or body region. In at least one embodiment, both axial deformation and compression using fluid 50 are used to impart two or three dimensional deformation in the phantom 10. For example, a lung phantom 10 may be deformed axially by a piston 42, as described above, and also hydrostatically using a fluid 50, thereby providing three dimensional deformation or motion. This multi-dimensional deformation may more accurately simulate the deformation of an organ or body region, such as the deformation of the lungs. In another embodiment, the flexible bladder(s) 48 are an internal bladder or bladders. The internal bladder(s) may be used to impart deformation from within the phantom 10. The bladder(s) may be inflated or deflated using a fluid 50 (e.g., water or air) to simulate deformation of, for example, a lung as air flows in and out of the bronchi and bronchioles. The flexible bladder(s) 48 may include one or more of the landmarks 24, sensors 26, and detectors 28. In embodiments having an internal bladder, this may assist in simulating internal cavities, such as air cavities in the lungs. Any of the above embodiments for causing deformation of the phantom 10 may be used alone or in combination with any or all of the other embodiments (e.g., piston and external bladder, piston and internal bladder, piston and both internal and external bladder, internal and external bladder, etc.).

[0043] Embodiments of the phantom 10 deformation systems are illustrated in Figures 1, 6, and 7. The systems include a phantom 10 formed of a deformable material 12 and including a plurality of landmarks 24, as described above. A plurality of radiation sensors 26 are disposed within the phantom 10, as well as at least one artificial tumor 18, which includes a radiation detector 28. The system further includes an actuator 52 configured to deform the deformable material 12, such as a motor-driven rod or piston 42 or a bladder 48 with pressurized fluid 50. A radiation source 54 is provided to irradiate the phantom 10. The radiation source may provide any type of radiation known for radiotherapy, for example, X-rays, electron beams, proton sources, or others. A video camera and/or 4D CT scanner (not shown) is configured to acquire location data from the artificial landmarks 24, and processor(s) (e.g., computer or computing devices) are used to process and record radiation data from the radiation sensors/detectors 26, 28. The location data and the radiation data may be generated and/or recorded while the phantom 10 is being deformed and irradiated.

[0044] In operation, the phantom 10 may be irradiated by a radiation source 54 while it is being deformed. As the phantom 10 is being deformed, the location of the plurality of landmarks 24 disposed therein may be tracked, for example, using a CT scanner. This tracked location data may be used to simulate deformation of the phantom 10 for various movements (e.g., simulate lung deformation during breathing). Measurements of radiation dose and/or accumulated dose may also be taken during phantom 10 deformation. These measurements may come from the radiation sensors 26 embedded in the phantom 10, radiation detectors 28 in the one or more artificial tumors 18, or a combination thereof. Therefore, both location and radiation data may be tracked during the deformation of the phantom 10. This data may be used to verify that 4D radiation treatment plans are providing the right amount of radiation to the right region at the right time and also that healthy tissue regions are not being subjected to excessive levels of radiation during a radiotherapy treatment.

[0045] Phantom 10 deformation may be induced in two dimensions: (a) a motor-controlled rod 42 may be used to compress and retract the phantom 10 material (e.g., sponge) in one dimension; and (b) a water pump may be used to infuse and remove water from a side-coupled cavity connected to the foam by a plastic membrane. The pressure exerted by the water will cause compression of the sponge in a direction perpendicular to that induced by the motor-controlled rod 42. The combination of force applied to the sponge in three dimensions will enable more realistic modeling of lung motion within a patient. The deformation applied in three dimensions will facilitate the study of patients who exhibit "diaphragmatic respiration" (forces applied mainly in the superior-inferior direction) as well as those who exhibit "chest-based respiration" (forces applied primarily in the anterior-posterior direction).

[0046] With continuing reference to Figures 1, 6 ,and 7, for the rod 42 driven phantom 10, a semi-sphere may be attached on the end portion 44 of the rod 42. The phantom 10 may be pressed against a rigid plate 56 (e.g., glass), and the plate 56 and the motor may be fixed to a smooth table 58 upon which the phantom 10 is positioned. For the water pump-driven phantom 10, the sponge may be compressed by a water-filled chamber 60 controlled by a water pump via a side-coupling cavity and connected to the sponge via a plastic membrane.

[0047] In one non-limiting example, a heterogeneous sponge lung phantom was placed in a latex cylinder and TLD-100 thermoluminescent dosimeters (ThermoFisher Scientific, Pittsburgh, PA) were placed at two locations in the sponge and one location inside an artificial tumor for 4D dosimetry verification. Three TLDs were used at each point for better statistics. 4DCT images were acquired while the piston was moving up to 2 cm at a rate of 10 cycles per minute. A 5 -beam 6MV 3D conformal plan was developed with 95% of the internal target volume (ITV) receiving the prescribed dose of 200 cGy, which may help to maintain a linear TLD response. The dose was calculated based on the maximum intensity projection (MIP) CT. The plan was delivered under the same deformation pattern with the BrainLab Novalis system, and exported to Eclipse and Pinnacle for TPS comparison. CT phase images were registered to end-exhale (EE) phase, when the sponge is maximally compressed, using a B-Spline-based Multi-Pass algorithm (VelocityAI). The resultant displacement vector field (DVF) was output for dose mapping. Dose was warped to EE phase using an in-house developed, subvoxel projection method and accumulated for comparison with the TLD measurements.

[0048] In addition to the deformable physical phantom 10 with embedded radiation detectors described above, the dosimetric phantom 10 may also utilize a calibrated database that contains the gold standard deformation fields and dose distributions for specific deformation scenarios. The phantom's deformation may be driven by a computer-controlled motor with pre-loaded motion patterns. In embodiments that also include a flexible bladder for fluid deformation, the computer may also control the flow of fluid that causes the deformation. The computer may be programmed to impart specific deformation patterns that may be of interest for a particular patient. Alternatively, standard or common deformation patterns that are applicable to multiple patients may be stored in the computer.

[0049] In at least one embodiment, the deformable phantom 10 may be used to verify a simulated radiation dosage. An algorithm for the verification may include first scanning the phantom 10 while applying a plurality of deformation patterns in order to generate and track location data for the artificial landmarks disposed in/on the phantom 10. This scanning may be done using any suitable equipment, for example, a CT scanner. Using the tracked location data, a displacement vector field (DVF) may be generated. The DVF may be generated by using an FEM model based on the tracked location data. Using a selected 4D radiation treatment and deformation pattern, radiation dosages in the phantom 10 may be measured during the deformation pattern. Simulated radiation dosages may be calculated for the same radiation treatment and deformation pattern. The measured and the simulated radiation dosages for the same radiation treatment and deformation pattern may then be compared to verify that the simulated dosages are accurate. If the simulated dosages differ from the measured dosages by over a certain amount (e.g., an acceptable error level), then parameters of the simulation may be adjusted and the simulation re -run and compared to the measured values again. This adjustment and re -run cycle may be repeated as necessary until the difference in the dosages is within an acceptable level.

[0050] The displacement of each point in the phantom 10 may be theoretically calculated and physically verified using the phantom 10, and the trajectory of each point is repeatable for different CT scans (e.g., in the case of patient simulation and daily treatment). Based on the displacement of the embedded markers, the phantom s displacement vector fields (DVF) can be calculated and verified using an algorithm 100 as follows: in step 102, the physical phantom 10 may be scanned by 4D CT for different deformation scenarios; in step 104, the positions of the landmarks embedded in the physical phantom 10 are identified from these 4D CT images; in step 106, with these tracked landmarks as boundary conditions, a FEM model of the physical phantom 10 may be developed to generate the phantom's DVF; in step 108, the FEM simulated DVF may be verified in step 110 using additional landmarks embedded within the phantom 10; in step 112, if there are large errors found in the FEM simulated DVF, the parameters of the FEM model may be adjusted (e.g., use the additional landmarks to re-simulate the phantom's deformation) in step 114; and steps 108 to 114 may be repeated until the accurate deformation field is derived in step 116. An embodiment of the method for generating and verifying a phantom 10 DVF based on FEM is illustrated in the algorithm 100 of Figure 8.

[0051] The embedded detectors may be capable of measuring radiation dose in heterogeneous materials that may have mass densities which change dynamically. The dose measured at any given point may be stable for the same deformation scenario. The dose may be measured at multiple points in the phantom 10 and recorded according to beam configurations, field sizes, and deformation patterns. These doses may be used to later verify 3D dose distributions.

[0052] According to an embodiment, 3D dose distributions may be created by a 4D Monte

Carlo dose computation system, and benchmarked with the dose measured at these selected points in the phantom 10. The calibrated dose distributions help provide point-wise dose verifications of 4D treatment plans that are developed by any other 4D dose calculation algorithms. The calibrated dose distributions are less impacted by the radiation measurement errors such as detector drift, response uncertainty, and mass-heterogeneity-induced dose interpretation errors as well as the non-realistic image pattern-induced registration errors.

[0053] Based on the standard DVF database, the database of the phantom 10's standard dose distributions may be calculated using an algorithm 200 as follows: in step 202, a 4D Monte Carlo (MC) dose calculation is performed on a static phantom; in step 204, with a 4D Monte Carlo (MC) method, radiation dose is computed at each voxel in the phantom 10, based on the validated FEM DVF; in step 206, the 4DMC calculated dose distributions are compared with actual dose measurements from a plurality of radiation treatments and deformation scenarios; in step 208, if dose errors above a pre-determined level are found in the comparison, the parameters of the 4DMC simulations will be adjusted in step 210; steps 202-210 may be repeated until the errors are reduced to an acceptable level in step 212. An embodiment of the method for generating and verifying 4D dose calculations is illustrated in the algorithm 200 of Figure 9.

[0054] Once an accurate model of accumulated dose has been developed, for example, using the algorithms 100 and 200 of Figs. 8 and 9, the accumulated dose distribution using clinical or other 4D algorithms can be calculated and compared to the 4DMC-FEM calculations. An embodiment of this method is illustrated in the algorithm of Figure 10. If the accumulated dose from the clinical or other 4D algorithms 304 is not within an acceptable level of the 4DMC-FEM dose 302, as determined in steps 306 and 308, the parameters of the clinical or other 4D algorithms may be adjusted in step 310 and the above steps repeated until the dose is within an acceptable level in step 312. [0055] Advantages of the phantom 10 according to the disclosed embodiments may include, but are not limited to: 1) the phantom deformation is repeatable and automatically controlled by a motor; 2) the phantom is composed of lung-like, heterogeneous materials with densities that can change dynamically; 3) radiation detectors are embedded to measure dose in each voxel during the phantom deformation; 4) standard deformation fields are created for different deformation scenarios including discontinuity, volume compression, surface slippage; and 5) standard dose distributions are created for different radiation and phantom conditions including different field size and energy, phantom heterogeneity, dynamic density variation, and volume compression.

[0056] Therefore, the disclosed phantom 10 may be composed of different layers of heterogeneous, compressible sponge suitable for verification of both image registration and dose mapping algorithms. The sponge material can be used without need for replacement after every irradiation. The phantom 10 may be enclosed in a flexible bladder and placed in a pressure- controlled, water-filled chamber, used to compress the phantom 10 in more than one dimension. The phantom 10 may be compressed with a semi-sphere attached to a cylinder, not air pressure, which may better simulate the natural breathing cycle. This allows different density changes at different locations during phantom 10 deformation.

[0057] In one non-limiting example, 4D dose calculation algorithms were verified using a deformable dosimetric phantom 10 according to the disclosed embodiments. Adaptive radiotherapy (ART) technique consists of two major components: deformable image registration (DIR) and dose accumulation. Verifying the accuracy of the two components is important, and a deformable lung phantom 10 is important for quality assurance of this technique. In this study, the phantom 10 included a lucite cylinder and a latex balloon that was attached to a piston that mimics the human diaphragm. The phantom 10 was programmed to simulate different breathing patterns. The balloon contained heterogeneous sponges and a tissue-equivalent tumor. An elevator held landmarks for motion tracking. 4DCT images were acquired using the RPM system. The piston's motion was programmed with amplitude of 2.5 cm, and films and TLDs were embedded.

[0058] For simulation of phantom 10 deformation, heterogeneous sponges may be suitable to evaluate different DIRs. Image registration may be performed between end-inhale (EI) and end- exhale (EE): A) from EI to EE; B) from EE to EI. Three DIR algorithms from VelocityAI are: Demons, "Deformable" with full intensity range (V-FIR), and "Deformable" with limited intensity range (V-LIR). One FEM algorithm developed for the phantom 10 disclosed herein is illustrated in Figure 11.

[0059] With respect to the results of DIR, Figure 12 is a graph of four DIR registrations from end-exhale to end-inhale, and Figure 13 is a graph of four DIR registrations from end-inhale to end- exhale. For the evaluation of DIR, Figure 14 depicts the consistence error between the registrations of FIGS. 8 and 9, namely:

[0060] Eq. 1 : E(A,B)=DIR(A)*DIR(B)

[0061] For dose calculation in this non- limiting example, 6MV Trilogy was simulated by

BEAMnrc, a 10x10 open beam was delivered to the phantom, the dose was calculated by DOSXYZnrc on the EE image, and the dose was mapped to EI. A user interface which may be used for dose calculation is illustrated in Figure 15. In this study, the CT density between EE and EI changed by 10.2% as the sponge was compressed. For dose reconstruction, a linear dose mapping (LDM) method is illustrated in Figure 16. For i satisfying p(i)=j, the reconstructed dose is:

[0062] Eq. 2: RD(i)=D(j)

[0063] An energy-mass congruence mapping (EMCM) method is another method of dose reconstruction, wherein energy and mass are warped to the EI image as shown in Figure 17. The dose is reconstructed using the following equations:

[0064] Eq. 3:

[0065] where

[0067] and

[0069] The results of dose reconstruction are shown in the graphs of Figures 18-19. The registration error-induced dose mapping inaccuracy was small. Note that the sharp dose gradient at the center of the beam was caused by a plastic bar present on the top of the phantom. Figure 20 is a graph of dose warped by EMCM and linear interpolation, showing different doses constructed by EMCM and LDM at the center of the phantom.

[0070] The differences at the center of the phantom were up to 8.3% for Demons and 5.8% for a Velocity. Their mean difference relative to their maximum dose is 1.0%, 0.33%, 0.35% and 0.30% for Demons, V-LIR, V-FIR and FEM, respectively, and their maximum difference is 13.2% at beam penumbra. In Table 1 below, the upper triangle shows displacement differences between two DIRs, and the lower triangle lists the relative dose differences calculated by EMCM with two related DIRs.

Table 1. Displacement and dose differences between two DIRs.

[0071] Therefore, in at least one embodiment, a deformable dosimetric phantom has been developed with heterogeneous, compressible materials. This phantom has manifested the variation of dose calculated with different image registration and dose addition algorithms. It is appropriate to serve as a quality assurance tool for verification of 4D dose calculation algorithms.

[0072] In another non-limiting example, a static test was performed to measure the accuracy and reproducibility of the experimental setup of the phantom. TLD measurements in the tumor agreed with Eclipse AAA and Pinnacle CCC were within 4.2% and 5.6% for two repeated trials. Reproducibility of the piston movement and target positions during compression cycles was verified by image overlay of two different CT scans at EE phase. After rigid image registration, the positions for the tumor and TLDs in the repeated scans were within 1 mm.

[0073] The measured tumor dose agreed very closely to the accumulated dose, 0.5%> lower with the TLDs. However, significant dose differences at points 1 and 2 outside the tumor were noted among different TPS algorithms. Point 1 was approximately 2 cm right of the tumor near the edge of the field, and was measured 112.3 cGy compared to the warped dose of 106.3 cGy. Point 2 at a high dose gradient region ~5mm left of the tumor was measured 156.1 cGy, while dose accumulation resulted in 178.2 cGy. Larger uncertainties in the TPS are expected in this gradient region. Table 2 below summarizes these results. Table 2 shows the dose measurement from TLDs compared to TPS and accumulated (warped) dose. PB = Pencil Beam, MC = Monte Carlo.

Table 2. Dose measurements from TLDs, TPS, and accumulated.

[0074] The planned dose from Pinnacle was warped to calculate the accumulated dose, improving the tumor dose calculation by 29.4%. The other two points were calculated in the sponge material, and may have larger errors associated with the TPS algorithms in these regions of low density material.

[0075] Benchmark models were developed from the CT images acquired from lung and prostate patients. For deformable image registrations performed on these models, DIR errors were evaluated on a large number of image voxels (multiple millions) using different regression methods. It was found that unbalanced force (UF), a DIR evaluation metric, outperforms the two generally used metrics: image intensity difference and inverse mapping composition. [0076] Simulation images were created with organs deformed of different magnitudes by

FEM and with simulated image noise imposed by FFT. With these simulation images, potential factors that may compromise the performance of DIR were investigated. A dosimetric impact index, μ, of DIR error at each image voxel with μ₁₍ defined as the maximum μ value per cc for each organ is provided. With this index, evaluation of the dosimetric consequences of DIR errors on ART based on tumor location, tumor volume, and patient sizes was performed.

[0077] The deformation of the physical phantom was derived using VelocityAI and evaluated with a landmark-based method. Dosimetry tests were conducted on the phantom first for a static case, to achieve 5% agreement between the measured doses and the doses calculated by four dose algorithms in three different planning systems, and then on its dynamic mode to verify the in- house developed dose accumulation algorithms.

[0078] DIR errors have been quantified in the treatment planning of lung and prostate cancer patients; their dosimetric consequences, represented by the dosimetric impact index μ_1(Χ, were calculalted for each organ. To assess the overall impact of these errors on adapted treatment plans, a new framework was developed to calculate patient-specific TCP for each adapted plan, presented an image based method to quantify radiobiological parameters (tumor survival fraction, tumor doubling time, and dead cell resolving time), and compared TCP with clinical assessment results. For NTCP, ventilation functions were used as a quantitative end-point to evaluate lung function for 27 lung cancer patients treated with SBRT. It was found that the average ventilation function is 1.25 for recurrent patients, higher than that for the non-recurrent patients.

[0079] While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention. Additionally, the features of various implementing embodiments may be combined to form further embodiments of the invention.

Claims

WHAT IS CLAIMED IS:

1. A phantom system for measuring radiation dosage comprising: a deformable material including a plurality of landmarks;

a plurality of radiation sensors disposed within the deformable material; at least one artificial tumor including a radiation detector disposed within the deformable material;

an actuator configured to deform the deformable material;

a radiation source for irradiating the deformable material; and

a processor configured to receive at least location data from the plurality of landmarks and radiation data from the plurality of radiation sensors and the at least one artificial tumor;

wherein at least a portion of the location and radiation data are recorded while the deformable material is being deformed and irradiated.

2. The phantom system of claim 1, wherein the deformable material is formed of a heterogeneous porous material.

3. The phantom system of claim 1, wherein the deformable material is formed of a plurality of adjacent slabs.

4. The phantom system of claim 3, wherein at least some of the plurality of radiation sensors are located at interfaces between the slabs.

5. The phantom system of claim 3, wherein at least one artificial tumor is located in each slab.

6. The phantom system of claim 3, wherein each slab is formed of the same material.

7. The phantom system of claim 3, wherein a portion of the slabs are formed of a heterogeneous sponge material and a portion of the slabs are formed of polyvinyl alcohol Cryogel (PVA-C).

8. The phantom system of claim 1, wherein the actuator includes a motor and a piston, the motor being configured to oscillate the piston to axially deform the deformable material.

9. The phantom system of claim 8, wherein the piston has an end portion having a spherical or semi-spherical shape, the end portion contacting the deformable material.

10. The phantom system of claim 1, further comprising a flexible bladder in contact with the deformable material and configured to receive a fluid and deform the deformable material.

11. The phantom system of claim 1, wherein the plurality of radiation sensors includes thermoluminescent detectors (TLDs) and the radiation detector includes a radiation- sensitive film.

12. A method of measuring radiation in a deforming phantom comprising:

deforming a phantom formed of a heterogeneous porous material and including a plurality of landmarks, a plurality of radiation sensors, and at least one artificial tumor including a radiation detector;

irradiating the phantom using a radiation source while the phantom is being deformed;

tracking a location of the plurality of landmarks while the phantom is being deformed; and

measuring a dosage of radiation in the radiation sensors and the at least one artificial tumor while the phantom is being deformed.

13. The method of claim 12, wherein the deforming step includes deforming the phantom in an axial direction.

14. The method of claim 12, wherein the deforming step includes deforming the phantom with a pressurized fluid.

15. The method of claim 12, wherein the tracking step is performed with a four- dimensional (4D) computed tomography (CT) scanner.

16. The method of claim 12, wherein the deforming step includes deforming the phantom to simulate lung deformation during breathing.

17. The method of claim 12, further comprising repeating the deforming, irradiating, tracking, and measuring steps for a plurality of radiation treatments and deformation patterns.

18. A method of verifying a simulated radiation dosage using a deformable phantom including a plurality of landmarks and a plurality of radiation sensors, the method comprising:

scanning the phantom while implementing a plurality of deformation patterns to generate and track location data for the plurality of landmarks;

generating a displacement vector field (DVF) of the phantom using the tracked location data;

measuring a radiation dosage in the phantom during a selected radiation treatment and deformation pattern using the plurality of radiation sensors;

calculating a simulated radiation dosage based on the DVF for the selected radiation treatment and deformation pattern; and

verifying the simulated radiation dosage by comparing it to the measured radiation dosage.

19. The method of claim 18, further comprising generating an FEM model of the phantom based on the tracked location data and using the FEM model to generate the DVF.

20. The method of claim 18, wherein if the simulated radiation dosage is different from the measured radiation dosage by more than a predetermined amount, parameters of the simulated radiation dosage are adjusted and the calculating and verifying steps are repeated.