image guided radiotherapy

8/6/2019 Image guided radiotherapy

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IGRT article[IMAGE GUIDED RADIOTEARPY (IGRT) ]

RAD 462 Image Guided Radiotherapy 1

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

image guided radiotherapy

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