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 XRV-100 and XRV-124 set up faster than film, produces 3D data more quickly, requires no human intervention, and has 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.
Advantages over Radiation Sensors
The XRV-100 and XRV-124 detect local gradients more accurately than radiation sensors, provides 3D information about the direction of the radiation, has finer resolution (with repeatability close to .05 mm) for positional information, and has a lower cost-per-test. Ionization chambers and diodes can only measure radiation at a single point in space. They 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 devices 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.
Advantages over Water Tank Systems
The XRV-100 and XRV-124 provides 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 medium are slow. Beam QA with this technique is typically done at commissioning and then annually for depth dose comparisons to commissioned values. For depth dose testing between annual water tank measurements, we are evaluating the use of the XRV-4000 with the LCW-200 (Logos Chevron Wedge), made with PMMA (acrylic) plastic.
2. Which QA test best highlights the capabilities of the XRV-100 and XRV-124?
The XRV-100/124 performs end-to-end tests quickly and accurately. Because the XRV-100/124 monitors the X-ray beam position and energy profile in real-time, the end-to-end tests can be repeated many times with different size beam widths, fully exercising all of the major subcomponents of the radiosurgery system in a single session.
The XRV-100/124 improves 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-100/124 directly measures the isocenter of the treatment beam, 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-100/124 test results are ready to view immediately 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 computer conveniently located adjacent to the treatment room.
3. What is the difference between the XRV-100, XRV-124, XRV-2000, XRV-3000, and XRV-4000?
The XRV-100 is a 3D phantom that takes the place of the patient on the treatment couch and is used for targeting and dose/fluence delivery testing. The XRV-100 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 the highest resolution of our 3D products. 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 60 degree imaging cone is 12 cm long, giving it a 70 mm field of view along the center axis.
The XRV-124 is a 3D phantom with the same format as the XRV-100, but with a larger and longer cone. It can perform the same vector, position, and profile measurements as the XRV-100 over a larger surface. This enables the XRV-124 to capture larger beam sizes at a wider variety of angles. The XRV-124 is capable of 3D measurements for FWHM beam diameters 6-60 mm. Vector position accuracy is 0.3 mm for small beams. The 45 degree imaging cone is 24 cm long, giving it a 140 mm long field of view along the center axis.
The XRV-2000 X-ray beam profiler is a 2D phantom with a flat 20 × 20 cm scintillator, and the XRV-4000 has a flat 30 × 40 cm scintillator. The unit is mounted in a 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. It can be used to measure the 2D position and profile of the treatment beam in real-time. BeamWorks 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-3000 Eagle X-ray beam profiler is a 2D phantom with a flat 31.5 × 31.5 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. Fiducials may be placed on the XRV-3000 target which is located directly over the scintillator surface.
4. Which radiosurgery systems are compatible with the XRV-100, XRV-124, XRV-2000, XRV-3000, and XRV-4000?
The XRV-100, XRV-124, XRV-2000, XRV-3000, and XRV-4000 are best used on X-ray therapy systems that can target a tumor using implanted fiducials or via recognition of bony features. This is called frameless or image guided radiotherapy (IGRT). The Accuray CyberKnife® and Varian TrueBeam® systems are examples of these machine types. The XRV systems are also useful with Varian Trilogy® and TomoTherapy® machines. XRV technology can also be used on image guided Proton therapy (IGPT) systems.
5. Can the XRV-100/124, XRV-2000, XRV-3000, and XRV-4000 be used with proton therapy systems?
Yes. Because the fundamental principles are the same for the overall hardware and software, the XRV-100, XRV-124, XRV-2000, XRV-3000, and XRV-4000 are compatible with proton therapy systems.
Here are several proton pencil beam scanning QA tests that can be performed with our digital camera phantoms:
- Gantry isocenter verification (XRV-100 or XRV-124).
- Alignment checking of lasers with image guidance and radiation isocenters (XRV-100 or XRV-124).
- PBS XY spot position accuracy (XRV-2000 Falcon or XRV-4000).
- Beam spot profiling (XRV-100, XRV-124, XRV-2000 Falcon, or XRV-4000).
- Rapid Bragg Peak constancy checks with the LCW-200 chevron wedge (XRV-2000 Falcon or XRV-4000).
- PBS XY scanning magnet SAD verification.
6. How do the XRV-100 and 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 contributed by many individual beams.
The XRV-100/124 determines the individual beam vectors, positions, and energy profiles by measuring the X-ray photons or fluence and how accurately those photons are delivered to a target in 3D space. These photons will produce the radiation dose by stripping the 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-100/124 captures and analyzes 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-100/124 should be thought of as an adjunct to the existing technologies of film, ion chambers, diodes, etc. Future additions to our VolumeWorks software will allow correlation of fluence patterns with dose.
7. Can the XRV-100 and XRV-124 perform patient specific QA?
A new Logos Systems software program, VolumeWorks, is in development that will use XRV captured beam data to reconstruct the delivered 3D dose volume, then compare that volume to the patient’s original 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 plan 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.
The American Association of Physicists in Medicine (AAPM) Task Group 142 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.
9. Why is radiosurgery system QA challenging to get right?
Current QA tools require a substantial amount of time to use properly. Tools that are tedious to use are tools that may not be used frequently enough to thoroughly test all aspects of a radiosurgery system. There is a need for QA tools like the XRV series that are easy to set up, easy to use, and that produce comprehensive data sets that are easy to understand.
10. What can happen when QA isn’t done correctly?
Every patient treatment is a risk. A radiation mistake can inflict serious injury on a patient, which is the 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.
A series of articles in the New York Times has described some of the tragic, and even fatal, results of treatments delivered at the wrong dose or in the wrong place.
The errors are occurring 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”
- “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