XRV-100 and IBAC Frequently Asked Questions
Contents
1. Why is radiosurgery
system Quality Assurance (QA) important?
2. What happens when QA isn't done correctly?
3. What makes radiosurgery system QA hard to get right?
4. What advantages does the XRV-100 have over other
calibration systems?
4.1 XRV-100 Advantages over Film
4.2 XRV-100 Advantages over
Radiation Sensors
4.3
XRV-100 Advantages over Water Tank Systems
5. Which QA test best highlights the capabilities of the
XRV-100?
6. How does the XRV-100 contribute to the measurement of the
radiation dose?
7. Can the XRV-100 perform patient specific QA?
8. What is the difference between the XRV-100 and the IBAC?
9. Which radiosurgery systems are compatible with the
XRV-100?
10. Can the XRV-100 be used with proton therapy systems?
1. Why is radiosurgery
system Quality Assurance (QA) important?
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.
2. What happens 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. In the second reference, flawed QA
is identified as responsible for 28% of radiation treatment mistakes. Hardware and software malfunctions contribute
to another 7% of the mistakes.
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
http://www.nytimes.com/2010/01/24/health/24radiation.html?_r=1
'Radiation Mistakes: One State's Tally'
http://www.nytimes.com/imagepages/2010/01/24/us/24radiation_graphic.html?ref=health
'The Radiation Boom: As Technology Surges, Radiation Safeguards
Lag' by Walt Bogdanich, 1/26/10
http://www.nytimes.com/2010/01/27/us/27radiation.html?fta=y
'The Radiation Boom: Case Studies:
When Medical Radiation Goes Awry' by Walt Bogdanich
1/26/10
http://www.nytimes.com/2010/01/27/us/27RADIATIONSIDEBAR.html
'Radiation Bills Raise Questions of
Supervision' by Walt Bogdanich and Rebecca R. Ruiz,
2/25/10
http://www.nytimes.com/2010/02/26/us/26radiation.html?fta=y
'At Hearing on Radiation, Calls for
Better Oversight' by Walt Bogdanich, 2/26/10
http://www.nytimes.com/2010/02/27/health/policy/27radiation.html?fta=y
3. What makes radiosurgery system QA
hard to get right?
Part of the problem is that 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
that are easy to set up, easy to use, and that produce comprehensive data sets
that are easy to understand.
4. What advantages does the XRV-100 have
over other calibration systems?
Existing dose measuring technologies
such as film, ionization chambers/diodes, and water tanks have their own specific
limitations. The XRV-100 compensates
for their limitations by providing more useful data, in a shorter time, with a
lower cost-penalty-per-test.
4.1
XRV-100 Advantages over Film
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 adds to the cost of a
test. The technician's time to position,
expose, and scan the film is a recurrent cost.
Film handling also introduces the potential for human error.
·
The XRV-100 sets up faster, produces
3D data more quickly, requires no human intervention, and has a lower cost-per-test.
4.2
XRV-100 Advantages over Radiation Sensors
Ionization chambers and diodes can
only measure radiation at a single point in space. They cannot detect local gradients in the
radiation field and cannot provide 3D information about the direction of the
radiation. These devices must be placed in
2D/3D 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 (4 to 10 mm), the sensor's resolution may be inadequate for providing
reliable 3D information for small diameter beams.
·
The XRV-100 detects local gradients,
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.
4.3 XRV-100 Advantages over Water Tank
Systems
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. The mechanisms needed to move the radiation
sensor through the medium are slow. Beam
QA with this technique is typically done on a yearly basis and provides no information
about the aiming accuracy of the robot/gantry.
The cost penalty for each test is high.
·
The XRV-100 provides real-time 3D
information, making it convenient to use daily or even before each
treatment. Because of the lower cost of an
XRV-100 unit and the much shorter time that the treatment room must be closed
to perform the tests, it has a lower cost-per-test.
5. Which QA
test best highlights the capabilities of the XRV-100?
The XRV-100 performs end-to-end tests
quickly and accurately. Because the
XRV-100 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 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 directly measures the isocenter
of the treatment beam, allowing it to detect asymmetrical beams or discontinuities
without making assumptions.
In addition, as soon as the
radiosurgery gantry stops moving and the beam is
turned off, the XRV-100 test results are ready to view. There is no radiochromic film that must first
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.
6. How does the XRV-100 contribute to the measurement
of the radiation dose?
A treatment plan usually consists of
many different radiation beams applied at different angles, shapes, energies,
and durations. 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.
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 verifies the 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.
The XRV-100 determines the beam vector,
position, and energy profile 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 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 should be thought of as an adjunct to the existing technologies of
film, ion chambers, diodes, etc.
7. Can the XRV-100 perform patient specific QA?
A module is in development that will
deliver XRV-100 test data in a format that can be used to compare delivered
beam data to the dose volume created in the patient's original treatment plan.
8. What is the difference between the XRV-100 and the IBAC?
The XRV-100 is a 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.
The IBAC is a collimator testing
device that directly attaches to the CyberKnife Iris and can measure the real-time
performance of the collimator beam shaping mechanism as well as the energy
profile of the beam as it emerges from the collimator. For simultaneous measurement of the beam direction,
it can be used in conjunction with the XRV-100.
9. Which radiosurgery systems are compatible with the
XRV-100?
The XRV-100 is best used on
radiosurgery 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-100 is also useful on Varian Trilogy and TomoTherapy machines.
10. Can the XRV-100 be used with proton therapy
systems?
Because the fundamental principles
are the same for the overall hardware and software, the XRV-100 is expected to be
compatible with proton therapy systems. We are actively seeking research partners in
this emerging field.
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