1. What advantages do the XRV-100 and XRV-124 have over other calibration systems?
The XRV-100 and XRV-124 provide more useful data, in a shorter time, with a lower cost-per-test than existing dose measuring technologies such as film, ionization chambers/diodes, and water tanks. They verify the 3D performance of the radiation delivery robot/gantry, tumor tracking cameras (kV imagers), beam shaping mechanism (MLC or Iris), and X-ray source (linear accelerator), and overall control system in real time with high accuracy. Complete QA plans that range in complexity from a simple Winston-Lutz to a non-isocentric volume can be captured directly to computer memory without pausing the treatment.
Advantages over Film
The 3D XRV-100 and XRV-124 cone-based systems set up faster than film, produce 3D data more quickly, require no human intervention, and have a lower cost-per-test. Film requires a technician’s time to position, expose, and scan it each time a new test is performed. A piece of film can only produce 2D information, so multiple pieces of film must be used to construct the 3D information needed to diagnose the delivery robot/gantry accuracy. Each piece of film and every block of time adds to the cost of a test. Film handling also introduces the potential for human error. Film inventory must be monitored and re-ordered when the stock dwindles. The XRV-100 and XRV-124 replace all of these film problems with a fast, easy to use, digital system.
Advantages over Radiation Sensors
The XRV-100 and XRV-124 detect local gradients more accurately than radiation sensors, provide 3D information about the direction of the radiation, have finer resolution (with repeatability close to .05 mm) for positional information, and have a lower cost-per-test. Ionization chambers and diodes can only measure radiation at a single point in space. Their 2D arrays cannot directly detect local gradients in the radiation field, cannot detect variations caused by the angle of the radiation, and cannot provide 3D information about the direction of the radiation. These sensors must be placed in planar or cylindrical 2D arrays to allow adequate data to be captured, which adds significantly to the test system cost and complexity. Because there are gaps between the individual devices (typically 4 to 10 mm), the sensor’s resolution may be inadequate for providing reliable 2D/3D information, particularly for small diameter beams. The XRV-100 and XRV-124 provide 3D results at higher resolutions than typical 2D radiation sensors.
Advantages over Water Tank Systems
The XRV-100 and XRV-124, which can be placed by hand onto the couch, provide real-time 3D information, making it convenient to use daily or even before each treatment, in the intervals between water tank testing sessions. In water tank systems, a single ionization chamber or diode is mechanically moved through a volume of water in order to develop 3D information about the radiation field. It provides no information about the aiming accuracy of the robot/gantry. The mechanisms needed to move the radiation sensor through the tank medium are slow. Beam QA with this technique is typically done at commissioning and then annually for depth dose comparisons to commissioned values. For proton range verification, our couch-top Ranger-300 Bragg Peak Imaging tool with the XRV-3000 Eagle or XRV-4000 Hawk provide accurate range measurements in a medium that is within 3% of equivalent water density.
2. Which QA test best highlights the capabilities of the XRV-124 and XRV-100?
The XRV-124 and XRV-100 cone-based systems perform image guided end-to-end tests quickly and accurately. Both 3D phantoms excel at gantry isocenter verification using multi-beam star-shot tests. Because the XRV-124 and XRV-100 monitor the X-ray or proton beam position and energy profile in real-time, the end-to-end tests can be repeated many times with different size beam widths or field sizes, fully exercising all of the major subcomponents of the radiosurgery system in a single session.
The XRV-124 and XRV-100 improve upon the industry standard Winston-Lutz test. Typically, Winston-Lutz style tests assume the beam is symmetrical with no discontinuities, and infers the isocenter position using calculations based on the penumbra. The XRV-124 and XRV-100 directly measure the gantry isocenter of the treatment beams, allowing it to detect asymmetrical beams or discontinuities that might be obscured by the central metal ball that is used in film measurements.
The XRV-124 and XRV-100 test results are ready to view as soon as the radiosurgery gantry stops moving and the beam is turned off. There is no radiochromic film that must be extracted from the phantom, hand carried to the scanner, subjected to the scanning process, etc. The XRV software immediately displays the full test results on a laptop computer conveniently located adjacent to the treatment room.
3. What is the difference between the XRV-100, XRV-124, XRV-2000 Falcon, XRV-3000 Eagle, and XRV-4000 Hawk?
3D scintillator cone-based systems
These 3D phantoms take the place of the patient on the treatment couch and are used for targeting and dose/fluence delivery testing. They can measure the vector location of the X-ray beam, the beam shape and intensity, and the pointing accuracy of the robot mechanism in real-time.
The XRV-100 has a 60 degree imaging cone that is 12 cm long, giving it a 70 mm long field of view along the center axis. With a vector position accuracy of up to 0.2 mm, it is ideal for measuring the rotational center of a system that uses beam diameters 3 - 30 mm (FWHM) in size.
The XRV-124 has a 45 degree imaging cone that is 24 cm long, giving it a 140 mm long field of view along the center axis, with similar accuracy as the XRV-100. Vector position accuracy is up to 0.3 mm for small beams. This enables the XRV-124 to capture larger beam sizes and fields at a wider variety of angles. The XRV-124 is capable of 3D measurements for beam diameters 4-60 mm (FWHM) in size.
2D scintillator flat-surface systems
These 2D beam profiler phantoms can be used to measure the position and profile of the treatment beam in real-time. BeamWorks Strata is the software program that controls the capture and analysis of beam data. Special features are included for "scanning window" style MLC measurements.
The XRV-2000 Falcon has a flat 20 × 20 cm scintillator. The Falcon comes with an auxiliary stand so that it can be positioned on its side for lateral beams, or it can be mounted in an optional gantry cradle that allows it to be manually turned a full 360 degrees. The scintillator can thus be positioned to be perpendicular to the incoming X-ray or proton beam at any angle of delivery from the treatment system gantry. Fiducials may be placed on the XRV-2000 Falcon target which is located directly over the scintillator surface.
The XRV-3000 Eagle has a flat 32 × 32 cm scintillator. The Eagle comes with an auxiliary stand so that it can be positioned on its side for lateral beams, or it can be mounted in an optional gantry cradle that allows it to be manually turned a full 360 degrees. The scintillator can thus be positioned to be perpendicular to the incoming X-ray or proton beam at any angle of delivery from the treatment system gantry. Fiducials may be placed on the XRV-3000 Eagle target which is located directly over the scintillator surface.
The XRV-4000 Hawk has a flat 42 × 32 cm scintillator. The mirror orientation is fixed to normally measure anterior/posterior beams. The unit comes with an auxiliary stand so that it can be positioned on its side for lateral beams, or it can be mounted in an optional gantry cradle that allows it to be manually turned a full 360 degrees. The scintillator can thus be positioned to be perpendicular to the incoming X-ray or proton beam at any angle of delivery from the treatment system gantry. Fiducials may be placed on the XRV-3000 Eagle target which is located directly over the scintillator surface.
4. Which radiosurgery systems are compatible with the XRV-124, Falcon, Eagle, and Hawk?
The XRV-124, XRV-2000 Falcon, XRV-3000 Eagle, and XRV-4000 Hawk are compatible with all image-guided photon, proton, and heavy ion radiotherapy systems. The lightweight hardware and the digital data-acquisition workflow are both designed to be general purpose. The hardware can be aligned using KV imagers or room lasers, and treatment plans can optionally be designed using CT scans of the XRV with its built-in fiducials.
After alignment, high-resolution video is recorded of the QA delivery as captured with the scintillator. Whether that delivery is a simple A-P and lateral beam pair from a linac, a complex modulated arc therapy delivery, a non-isocentric robotic delivery, or a scanned proton beam field, it is recorded with film-like resolution and the convenience of an all-digital data path. Afterward, a variety of software modules are used to perform the specialized analyses needed for particular QA tests.
X-ray therapy customers have successfully employed XRV systems with their Accuray CyberKnife®, TomoTherapy®, Varian TrueBeam®, Trilogy®, Elekta Synergy®, and many other systems.
Since the fundamental operating principles are the same, XRV technology can also be used on Image Guided Proton Therapy (IGPT) and Intensity Modulated Proton Therapy (IMPT) systems. Proton therapy customers enjoy using their XRV systems on IBA, Varian, Sumitomo, Hitachi, Mevion, ProNova, Protom, Toshiba, and Mitsubishi systems.
5. Can the XRV-124, Falcon, Eagle, and Hawk be used with proton therapy systems?
Yes. Because the fundamental principles are the same for the overall hardware and software, the XRV-124, XRV-100, XRV-2000 Falcon, XRV-3000 Eagle, and XRV-4000 Hawk are compatible with proton and heavy ion therapy systems.
Here are several proton pencil beam scanning (PBS) QA tests that can be performed with our digital camera phantoms:
- Gantry isocenter verification (XRV-124/100).
- Alignment checking of laser, image guidance, and radiation isocenters (XRV-124, XRV-100).
- PBS XY spot position accuracy (XRV-124, XRV-2000 Falcon, XRV-3000 Eagle, or XRV-4000 Hawk).
- Beam spot profiling (XRV-124, XRV-100, XRV-2000 Falcon, XRV-3000 Eagle, or XRV-4000 Hawk).
- Proton Bragg Peak range verification with the Ranger-300 module (XRV-3000 Eagle or XRV-4000 Hawk).
- Rapid Bragg Peak constancy checks with the LCW-200/300 chevron wedge (XRV-2000 Falcon, XRV-3000 Eagle, or XRV-4000 Hawk).
- PBS flat-field uniformity verification (XRV-124, XRV-2000 Falcon, XRV-3000 Eagle, or XRV-4000 Hawk).
- PBS XY scanning magnet SAD verification.
The XRV-3000 Eagle and XRV-4000 Hawk phantoms have a slot which holds the standard scintillator. Once removed, the Ranger-300 module (see below) can then be inserted for proton range verification.
The Ranger-300 consists of a rectangular block of scintillating plastic 305 millimeters long which acts to slow down and stop incoming protons. The light produced by the scintillator creates an image of the Bragg peak which is recorded by the Eagle or Hawk digital camera.
The 55 x 55 mm scintillator cross-section can be used to image beams up to 30-mm in diameter. The approximately 1.03 water equivalence ratio of the scintillator means beams between 50 and 225 MeV are visible - additional buildups are provided to capture higher-energy beams.
The BraggPeakView software provides manual or automated measurement of the R100, P80/D80, P90/D90, and D80/D20 locations on each proton beam image. Sophisticated Excel templates are provided for analyzing any number of beam measurements calculating individual and average error values for the group.
6. How do the XRV-124 measurements relate to radiation dose?
The delivered dose of radiation from a single beam is based on the location of the beam, the kind of tissue it is traveling through, the initial energy of the beam, the shape of the beam, and how long the beam is on. A treatment plan usually consists of many different radiation beams applied at different angles, shapes, energies, and durations. Consequently, the therapeutic dose is a three-dimensional volume located within the patient or phantom, with each point in the volume having a unique amount of delivered radiation.
The XRV-124 and XRV-100 determine the individual beam vectors, positions, and energy profiles by measuring the X-ray photons, or fluence, and by measuring how accurately those photons (or protons) are delivered to a target in 3D space. The photons will produce radiation dose by stripping electrons off of the atoms in its path. If the photons are not delivered in an accurate fashion, the dose will not be accurate.
The XRV-124 and XRV-100 capture and analyze X-ray fluence, not dose. Measuring fluence is in many ways superior to measuring dose, but since dose-based measurements are the industry standard, the XRV-124 and XRV-100 should be thought of as an adjunct to the existing technologies of film, ion chambers, diodes, etc.
The XRV-124 has an optional add-on called the Dose Post which allows it to accept a small ion chamber (or scintillating fiber) to measure dose at a point on the central axis of the cone with build-up. The Dose Post data at the center of the build-up can be correlated with the 3D fluence map that the XRV-124 VolumeWorks application creates from a delivery, producing a 3D representation of the dose distribution inside the cone.
7. Can the XRV-124 perform patient specific QA?
A new Logos Systems software program, VolumeWorks, is in development that will use XRV captured beam data and dosimetric data from the optional Dose Post imaging cone add-on to reconstruct the delivered 3D dose volume. The VolumeWorks 3D dose volume can then be compared to the original QA treatment plan.
8. How often should radiosurgery system QA be performed?
Calibration is essential to confirm the accuracy of the treatment system. The success of any treatment requires that the beam be delivered exactly where it is aimed, and that the actual beam energy profile matches the expected beam energy profile used by patient treatment planning software. To achieve this concurrence, ‘baseline’ data is collected at commissioning and then scheduled clinical QA procedures are carried out as long as the system is in service.
The American Association of Physicists in Medicine (AAPM) Task Group 142 (Quality Assurance of Medical Accelerators) recommends a daily complete end-to-end test of both imaging guidance and therapy radiation to ensure that patients are being given a maximum therapeutic dose at the tumor and that nearby organs at risk are not being damaged in the process. "It is, therefore, critical to ensure the coincidence of these two coordinate systems for different clinical needs of image-guided radiation therapy procedures... The accuracy of this process should be done on the daily basis, especially for SRS/SBRT."
Additionally, Task Group 224 (Comprehensive Proton Therapy Machine Quality Assurance) presents tolerance recommendations for proton-specific daily, weekly, monthly, and annual QA procedures. The procedures listed include verification of proton range, SOBP width, spot constancy, field flatness, gantry angle, and gantry isocenter, among other parameters.
Some of our proton customers with multiple gantries use their XRV-124 daily for beam alignment verification.
9. How can proton system manufacturers benefit from using Logos Systems QA products?
Proton therapy system manufacturers can gain great productivity benefits both when commissioning a new system and during night-time/weekend QA by employing the BeamWorks Client-Server software.
The Client-Server software is a remote operation toolkit which allows Logos phantoms such as the XRV-124 or XRV-4000 Hawk to be tightly integrated with the treatment system’s Beam Position Control software. A network-connected computer is made to control beam acquisition and measurement programmatically, so that beam position or profile errors can be automatically mapped and corrected according to gantry angle. The resulting reduction in manual data processing allows the team to accomplish more beam vector/position tuning in a shorter time frame.
10. How are Logos Systems phantoms used for proton commissioning?
AAPM Task Group 185 (Clinical Commissioning of Intensity-modulated Proton Therapy Systems) recommends that commissioning teams carry out proton beam fluence profile evaluation, Integral Depth-Dose (IDD) curve development, and end-to-end verification. A link to the report (starting on page 2 of the document) is provided below.
The Logos Systems XRV-124 and XRV-4000 Hawk phantoms have been used in clinical commissioning by multiple facilities for fluence profile evaluation (TG 185 11.D.2), spot position verification, and end-to-end gantry isocenter characterization (TG-185 12B) [1-3]. Additionally, Logos recommends the collection of baseline proton range data using the Ranger-300 concurrent with IDD curve development (TG-185 11.D.1).
11. What can happen when QA isn’t done correctly?
Every patient treatment has risk. A radiation mistake can inflict serious injury on a patient, which is a top concern of the clinic. The effects can ripple outward to include legal expenses, damage to the institution’s reputation, and loss of confidence by the customer base.
In 2010, the New York Times reported an eye-opening series of articles detailing the results of treatments delivered at the wrong dose or in the wrong place.
The errors occurred despite the use of these institutions’ standard QA procedures.
- “The Radiation Boom: Radiation Offers New Cures, and Ways to Do Harm” by Walt Bogdanich, 1/23/10
- “Radiation Mistakes: One State’s Tally” 1/24/10
- “The Radiation Boom: As Technology Surges, Radiation Safeguards Lag” by Walt Bogdanich, 1/26/10
- “The Radiation Boom: Case Studies: When Medical Radiation Goes Awry” by Walt Bogdanich 1/26/10
- “Radiation Bills Raise Question of Supervision” by Walt Bogdanich and Rebecca R. Ruiz, 2/25/10
- “At Hearing on Radiation, Calls for Better Oversight” by Walt Bogdanich, 2/26/10
Nationwide cancer clinic SRS treatment delivery verification is performed by MD Anderson's Imaging and Radiation Oncology Core (IROC) program. In 2016, 103 IROC anthropomorphic phantoms were irradiated by participating proton therapy centers. Their results indicated a phantom pass rate of 79% with generous tolerances.
IROC cited significant room for improvement in the areas of TPS dose agreement, range calculations, motion management, and multiple-target irradiation.
Our mission at Logos Systems is to make comprehensive QA an efficient, intelligent, and enjoyable experience so that patients can receive the best possible care.