Download - Image guided radiotherapy
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IGRT article[IMAGE GUIDED RADIOTEARPY (IGRT) ]
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Table of Contents
Abstract . 2
Aims . 2
Subject & Method .. 2
Introduction .. 3
IGRT technology and its benefits .... 5
The modality used in IGRT . 10
Fluoroscopy ....10
CT 11
CBCT 12
MVCT .12
Optical Tracking ..13
Clinical applications of IGRT ....14
Prostate 15
Conclusion .17
The references .19
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Abstract
IGRT is the most advanced technology to track
cancer and spare normal tissues. This advanced
technology allows radiation to be delivered to tumors
with more precision than was traditionally possible. The
ability to define a more precise location of the
tumor, means a smaller radiation field can be used, so
there is less radiation damage done to normal tissue. This
technology decreases the radiation dose to normal tissue,
thus decreasing side effects and improving outcomes.Computed tomography (CT), magnetic resonance
imaging (MRI), positron emission tomography (PET),
ultrasound (US) and x-ray imaging may be used for
IGRT.
AIMS
Disscues the IGRT technology and its benefits.List the modalities used in IGRT.Identify the clinical application of IGRT.
Subject & Method
The data is obtained by secondary data from several
websites and online journals.
Introduction
The Image Guided Radiation Therapy (IGRT) is now
widely appreciated in the radiotherapy community.
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Image guided radiation therapy is a major technical
innovation of radiotherapy. It allows locating the tumor
under the linear accelerator just before the irradiation, by
direct visualization (3D mode soft tissue) or indirectvisualization (2D mode and radio-opaque markers). The
technical implementation of IGRT is done by very
different complex devices. The most common modality
is the cone beam CT, because it's available in any new
accelerator. These advances allowed radiation
oncologists to better see and target tumors, which have
resulted in better treatment outcomes, more organ
preservation and fewer side effects. IGRT enables
patients to be repositioned to improve their setup
accuracy, and the accuracy of their treatment,
immediately before the radiation dose is delivered.
IGRT produces planar images, on film or digital
detectors, to image the bony anatomy and so verify theposition of the treatment fields. This method assumes the
position and shape of the tumor and critical surrounding
normal tissues are fixed with respect to
the bony anatomy, which is often not the case, and relies
on planar megavoltage images which are not very clear.
Both of these problems have been solved by the advent
of IGRT in which kilovoltage imaging equipment, as
used in diagnostic radiology, has been attached to theLINAC to produce planar images at the time of treatment
which are superior to the traditional megavoltage images.
This latest technology can also be used to generate cone-
beam CT (CBCT) images to visualize the tumour and
surrounding healthy tissue and daily changes in shape
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and position of both immediately prior to each
treatment. The use of
IGRT, including CBCT, enables patients to be
repositioned to improve their setup accuracy, and theaccuracy of their treatment, immediately before the
radiation dose is delivered.
IGRT technology and its benefits
Guiding the placement of the treatment field is not a
new concept. Since the advent of fractionated radiation
therapy for the treatment of disease, techniques have
been employed to help ensure the accurate placement of
a treatment field. In general, at the time of 'planning'
(whether a clinical mark up or a full simulation) the
intended area for treatment is outlined by the radiation
oncologist. Once the area of treatment was determined,
marks were placed on the skin. The purpose of the ink
marks was to align and position the patient daily for
treatment to improve reproducibility of field placement.
By aligning the markings with the radiation field (or its
representation) in the radiation therapy treatment room,
the correct placement of the treatment field could be
identified. Over time, with improvement in technology
light fields with cross hairs, isocentric lasers and with
the shift to the practice of 'tattooing' - a procedure where
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ink markings are replaced with a permanent mark by the
application of ink just under the first layer of skin using a
needle in documented locations - the reproducibility of
the patients setup improved.
Delivery of radiation therapy requires a treatment
team, including a radiation oncologist, therapeutic
medical physicist, dosimetrist and radiation therapists.
The radiation oncologist is a physician who evaluates the
patient and determines the appropriate therapy or
combination of therapies. The physician determines what
area to treat and what dose to deliver. Together with thetherapeutic medical physicist and the dosimetrist, the
radiation oncologist determines what techniques to use to
deliver the prescribed dose. The physicist and the
dosimetrist then make detailed treatment calculations.
Radiation therapists are specially trained technologists
who acquire images and deliver the daily
treatments.Regardint to IGRT, The equipment is
operated by a radiation therapist, a highly trainedtechnologist. The overall treatment plan is created and
supervised by the radiation oncologist, a highly trained
physician specializing in treating cancer with
radiotherapy.The linear accelerator, are equipped with imaging
technology so that the physician can image the tumor
immediately before or even during the time radiation isdelivered, while the patient is positioned on the treatment
table. Using specialized computer software, these images
are then compared to the images taken during simulation.
Any necessary adjustments are then made to the patient's
position and/or radiation beams in order to more
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precisely target radiation at the tumor and avoid healthy
surrounding tissue. Computed tomography (CT),
magnetic resonance imaging (MRI), positron emission
tomography (PET), ultrasound (US) and x-ray imagingmay be used for IGRT. there is no specific preparation
for IGRT, other than the preparation for routine radiation
therapy delivery
IGRT is used to treat tumors in areas of the body that
are prone to movement, such as the lungs (affected by
breathing) and prostate gland, as well tumors locatedclose to critical organs and tissues. It is often used in
conjunction with intensity-modulated radiation therapy
(IMRT), an advanced mode of high-precision
radiotherapy that utilizes computer-controlled x-ray
accelerators to deliver precise radiation doses to a
malignant tumor or specific areas within the tumor.
Local or regional control of a tumor is the ultimate
goal of an overall treatment strategy, especially for a
patient with cancer. Failure to achieve tumor control can
result in a greater likelihood of developing distant
metastases, continued tumor growth, severe debilitation
or even death of the patient . IGRT also can be used to
measure and correct positional errors for target andcritical structures immediately prior to or during
treatment delivery. The patient is localized in the
treatment room in the same position as planned from the
reference imaging dataset. An example of Three-
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dimensional (3D) IGRT would include localization of a
cone-beam computed tomography (CBCT) dataset with
the planning computed tomography (CT) dataset from
planning. Similarly Two-dimensional (2D) IGRT wouldinclude matching planar kilovoltage (kV) radiographs
fluoroscopy or megavoltage (MV) images with digital
reconstructed radiographs (DRRs) from the planning CT.
Before treatment, the patient is simulated on an X-
ray machine or CT scanner for treatment planning. The
patients skin is marked with ink or a small tattoo at a
specific point in 3-D space so that a treatment plan may
be specifically designed to fit each patient. The images
from simulation are sent to a computer brought back on a
different for planning and the patient is day for the start
of the actual treatments. Prior to each daily treatment,
the radiation oncology team aligns the patient with room
alignment lasers pointed at the patients skin marks.
Traditionally, portal films were taken once a week to
ensure that the patients skin marks are still in alignment
with bony anatomy. The accuracy of traditional radiation
therapy is five to 10 millimeters. With IGRT, daily setup
error has been reduced to within one to two millimeters
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In addition, daily (instead of weekly) images are taken
to assist with accuracy.
The goal of the IGRT process is to improve the
accuracy of the radiation field placement, and to reduce
the exposure of healthy tissue during radiation
treatments. By improving precision and accuracy through
IGRT, radiation is decreased to surrounding healthy
tissues, allowing for increased radiation to the tumour for
control. The clinical benefit for the patient is the ability
to monitor and adapt to changes that may occur during
the course of radiation treatment. Such changes can
include tumour shrinkage or expansion, or changes inshape of the tumour and surrounding anatomy.
The used modalities for IGRT
Fluoroscopy
Fluoroscopy is an imaging technique that uses a
fluoroscope, in coordination with either a screen orimage-capturing device to create real-time images of
patients internal structures.
Computed tomography (CT)
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A medical imaging method employing tomography
where digital geometry processing is used to generate a
three-dimensional image of the internal structures of an
object from a large series of two-dimensional X-rayimages taken around a single axis of rotation. CT
produces a volume of data, which can be manipulated,
through a process known as windowing, in order to
demonstrate various structures based on their ability to
attenuate and prevent transmission of the incident X-ray
beam.
Conventional CT
With the growing recognition of the utility of CT
imaging in using guidance strategies to match treatment
volume position and treatment field placement, several
systems have been designed that place an actual
conventional 2-D CT machine in the treatment room
alongside the treatment linear accelerator. The advantage
is that the conventional CT provides accurate measure of
tissue attenuation, which is important for dose
calculation.
Cone beam
cone-beam computed tomography (CBCT) based image
guided systems have been integrated with medical linear
accelerators to great success. With improvements in flat-
panel technology, CBCT has been able to providevolumetric imaging, and allows for radiographic orfluoroscopic monitoring throughout the treatment
process. Cone beam CT acquires many projections over
then entire volume of interest in each projection. Using
reconstruction strategies pioneered by Feldkamp, the 2D
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projections are reconstructed into a 3D volume
analogous to the CT planning dataset.
MVCT
Megavoltage Computed Tomography is a medical
imaging technique that uses the Megavoltage range of X-
rays to create an image of bony structures or surrogate
structures within the body. The original rational for
MVCT was spurred by the need for accurate density
estimates for treatment planning. Both patient and targetstructure localization were secondary uses. A test unit
using a single linear detector, consisting of 75 cadmiumtunstate crystals, was mounted on the linear accelerator
gantry. The test results indicated a spatial resolution of
.5m, and a contrast resolution of 5% using this method.
While another approach could involve integrating the
system directly into the MLA, it would limit the number
of revolutions to a number prohibitive to regular use.
Optical Tracking
The use of a camera to relay positional information of
objects within its inherent coordinate system by means of
a subset of the electromagnetic spectrum of wavelengths
spanning ultra-violet, visible, and infrared light. Optical
navigation has been in use for the last 10 years within
image guided surgery (neurosurgery, ENT, and
orthopaedic) and has increased in prevalence withinradiotherapy to provide real-time feedback throughvisual cues on graphical user interfaces (GUIs). For the
latter, a method of calibration is used to align the
cameras native coordinate system with that of the
isocentric reference frame of the radiation treatment
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delivery room. Optically tracked tools are then used to
identify the positions of patient reference set-up points
and these are compared to their location within the
planning CT coordinate system. A computation based onleast-squares methodology is performed using these two
sets of coordinates to determine a treatment couch
translation that will result in the alignment of the
patients planned isocenter with that of the treatment
room. These tools can also be used for intrafraction
monitoring of patient position by placing an optically
tracked tool on a region of interest to either initiate
radiation delivery (i.e. gating regimes) or action (i.e.repositioning).
Clinical application of IGRT
Most cancers will benefit from treatments that are
more accurate and precise. Tumors of the prostate, brain
and head and neck region are treated using IGRT to
ensure that delicate tissues such as the rectum, urethra,
spinal cord and salivary glands remain away from the
higher dose of radiation that is delivered to the tumor. At
North Shore Radiation Therapy, IGRT is used in with
other advanced technologies such as Stereotactic
Radiosurgery, Respiratory Gating and IMRT (Intensity
Modulated Radiation Therapy).
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Tumors of the brain, head and neck region fare well
when treated using IGRT because the technology ensures
that the delicate tissues, such as the spinal cord and
salivary glands remain away from the high dose region.IGRT can ensure that the head and neck position is so
precise that doses to the spinal cord and vital organs can
be significantly reduced or eliminated.
Lung and breast cancers will benefit from IGRT
and other technologies such as Respiratory Gating and
IMRT by taking breathing motion into consideration, anddecreasing radiation doses to the lungs and heart. It has
been shown that unnecessary radiation to these organs
can create significant problems after treatment, such
as secondary cancers.
PROST
ATE
When treating prostate cancer with IGRT, we see
significant benefits. As the bladder fills and empties, the
prostate moves, sometimes significantly. This means
that the prostate will be in different positions for each
day of radiation treatment. So before the treatment,
IGRT is given to ensure a more precise delivery of
radiation.
Before the treatments begin, the urologist will
implant small fiducial markers into the prostate utilizing
a simple procedure to direct the radiation oncologist to
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Pre-IMRT IMRTDose Sculpting
IMRT + IGRTDose Sculpting + Targeting
High Dose
y Improved Outcomesy Reduced Side Effects
the exact location of the prostate. During the treatment,
state-of-the-art imaging will be used to locate these
markers every day and the treatment machine will be
realigned to ensure that the prostate is exactly where itshould be during your treatment (See fig.1).
Figure 1. an example of the benefits of IMRT/IGRT in prostate
cancer treatment.
CONCLUSION
IGRT or Image Guided Radiation Therapy is the
most advanced technology to track cancer and normal
tissues and spare normal tissues. . This is very useful
since tumors can move between treatments due to
differences in organ filling or movements while
breathing. These advances allowed radiation oncologists
to better see and target tumors, which have resulted in
better treatment outcomes, more organ preservation and
fewer side effects.
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IGRT decreases radiation dose to normal tissue,
decreases side effects and improves outcomes.CT, MRI,
PET, US, and x-ray imaging may be used for IGRT. At
the beginning of each radiation therapy session, thepatient is carefully positioned guided by the marks on the
skin defining the treatment area. Devices may be used to
help the patient maintain the proper position. Images are
then taken using imaging equipment that is built into the
radiation delivery machine or mounted in the treatment
room. The physician then reviews the images and
compares them to the images taken during simulation.
The patient may be repositioned and additional imagingmay be performed. After any necessary adjustments are
made to the treatment plan and patient positioning,
radiation therapy is then delivered. The image-guidance
process may add up to five minutes to each radiation
therapy session.
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The references
http://www.cancer-radiation.com/index.php/external-beam-radiation-
therapy-treatments/what-is-igrt
http://en.wikipedia.org/wiki/Image-guided_radiation_therapy
http://www.radiologyinfo.org/en/info.cfm?pg=IGRT
http://www.northerncalprostatecare.com/index.php?option=com_content&view=article&id=24&Itemid
=3
http://advancedradiationcenters.com/?p=whatisigrt