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Image Guided Radiation Therapy
Dr. Mark Fisher
School of Computing Sciences
UEA Norwich UK
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Plan
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Introduction/Motivation
Background
State of the Art
Current Research
Conclusions
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Introduction/Motivation
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Introduction
• Cancer is currently the cause of 12% of all deaths world
wide; 10 million new cases diagnosed annually.
• Within the European union over 1,5 million new cancer cases
are diagnosed every year and over 920000 people die of
cancer.
• Most scientists are confident that in the long term
significant improvement in cancer cure will come from
systematic treatments such as immunotherapy and/or gene
therapy and drug targeting.
• For the time being the surgical removal of the tumour tissue
followed by radiotherapy remains the main method of
treatment.
Source: MAESTRO 2004
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New cases and deaths from cancer - US 2004
Site
% New Cases
Est. Deaths
Digestive System
19%
134,840
Prostate
17%
29,900
Breast
16%
40,580
Respiratory System 14%
165,130
Source: American Cancer Society, 2005
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Radiation treatment equipment per million population
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Background
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Background
Ionising
Electromagnetic
Radiation interacts with
cells destroying their
DNA
BUT...
Both malignant and nonmalignant tissue is
destroyed
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None-malignant cells can repair
themselves but high doses of
radiation to healthy tissue can
induce secondary malignancies.
Aim of Radiotherapy Treatment I
• To deliver a high dose of Radiation to the tumour while
and a low dose to healthy tissue and organs at risk.
– Possible through the use of multiple treatment fields (beams).
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Radiation Therapy Treatment Delivery
1895
Wilhelm Conrad Roentgen saw
the bones of his own hand when
held between cathode tube and
fluorescent screen.
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Radiation Therapy Treatment Delivery
1912
The Coolidge Tube.
William Coolidge of GE with his "hot" cathode tube,
The Coolidge tubes also made possible the development
of orthovoltage kV X-ray therapy.
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Radiation Therapy Treatment Delivery
1937
Varian brothers develop first klystron
tube, initially used in Radar
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Radiation Therapy Treatment Delivery
1953
Mullard (Philips) 4 MV double gantry linac.
First installed at Newcastle Hospital,
This unit featured a nearly isocentric
mount, a 1 meter traveling wavetube,
MV magnetron, and a false floor.
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Radiation Therapy Treatment Delivery
1990s
Varian Clinac treatment unit, Today's
integrated medical linac has been enhanced
by computerized controls and easier operation
in the quest for optimal treatment in cancer.
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Radiation Therapy Treatment Planning
• In the early days of radiotherapy, the X-ray beams were
rectangular or square in shape and were directed at the
tumor from two to four different angles.
– Since the dosages delivered were uniform in strength there was
some damage to healthy tissue.
• In the 1970’s conformal RT was developed. This approach
used lead-alloy blocks to shape the beam.
– The dose was ‘conformed’ to the shape of the tumour, healthy tissue
is spared.
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ICRU 50/62
ICRU 50 (1993) and ICRU 62 (1999)
define relationships and margins
between treatment volumes
Report of BIR working party (2003),
established in 1999 following
initial work by Euen Thompson, NNH
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State-of-the-Art
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Intensity Modulated Radiotherapy Treatment
(IMRT)
Conceptualised in 1980’s
Uses Multi-leaf collimator
to vary the dose density
within the treatment
volume.
Allows for much higher dose
delivery to malignant tissue.
Needs higher precision
volumetric planning
systems
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Currently the
most widely
deployed method
in clinical use.
Beam shaping using MLC
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To treat each patient
• a medical linac with a multi-leaf collimator ($1.6M)
• treatment planning software with inverse
treatment planning capability
• simulation devices and software for establishing
patient positioning as well as pre-testing and
refining treatment plans
Total Cost approx. £3M each system
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Comparisons between IMRT and 3D-CRT Treatment Costs
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Data Acquisition
Source: NNUH
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Treatment Planning
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Computer Planning
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Plan Simulation/Verification
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Five field IMRT beam arrangement for treating prostate
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Treatment Delivery
Treatment is
delivered over
30-40 fractions
Patient makes
several visits
to hospital
over a period
of weeks
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Accounting For Organ Movement
• “Most of the development of IMRT has taken place
assuming that the organs don't move from fraction to
fraction and are well represented by their positions
determined from some pre-planning 3D imaging study, be it
x-ray CT, MR or functional imaging. As the ability to
conform to the target has now reached near perfection,
attention is now turning to not accepting this limitation and
attempting to quantitate organ movement and account for it
in IMRT planning and delivery”.
• “IMRT of the moving patient is like completing a jigsaw on a
jelly”
Prof. Steve Webb, Royal Marsden Hosp.
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Types of Motion
• Patient set-up errors
– Position-related organ motion which can be minimised if the patient's
planning scan is performed while the patient is immobilised and in the
treatment position.
• Inter-fraction motion
– i.e. motion that occurs when the target volume changes from day to
day. This is a problem for organs that are close to or part of the
digestive/excretory system. This work is collated under various
headings: gynaecological tumours, prostate (the largest group),
bladder and rectum.
• Intra-fraction
– generally due to respiratory and cardiac functions which disturb
other organs. This work is collated under headings: liver, diaphragm,
kidneys, pancreas, lung tumours and prostate.
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Patient Set-up Errors
Stereotactic surgery
uses mechanical fixations
implanted in the skull
to ensure alignment.
Gold markers may be implanted
in soft tissue
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Intra-Fraction Motion: Current Approaches
Passive infra-red reflective marker block used to
track chest wall motion during data acquisition,
simulation, and treatment.
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Varian RPM respiratory gating
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Gated 4D CT
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Beam’s Eye Views of gated and non-gated treatment volumes
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Gated 4-D CT Movie showing Lung Motion
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MotionView™: addresses intra-fraction deformation
This offers particular advantages
for targeting lung tumors which
move and deform during respiration.
Flat panel Amorphous Silicon Detector
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Inter-fraction Motion: Current Approaches
Image Guided Radiation Therapy (IGRT)
• Traditionally, imaging technology has been used to produce
three-dimensional scans of the patient’s anatomy to identify the
exact location of the cancer tumor prior to treatment.
• However, difficulty arises when trying to administer the
radiation, since cancer tumors are constantly moving within
the body
• IGRT combines a new form of scanning technology, which allows
planar or X-ray Volume Imaging (XVI), with IMRT. This enables
physicians to adjust the radiation beam based on the position of
the target tumor and critical organs, while the patient is in the
treatment position.
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Elekta Synergy™
Source: Elekta
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Elekta Synergy™
Synergy allows for coregistration of ConeBeam CT and RTP data
in real-time
immediately before
treatment delivery
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“For the first time the cone beam system lets us see what we want
to hit with our treatment by giving us a continuous set of detailed
3-D X-ray images of the patient when the patient is lying
down on the treatment couch. This means we can even move
towards better cure rates by safely increasing the doses we deliver
in radiotherapy.”
(Professor Chris Moore, Consultant Physicist, Christie Hospital)
Available from August 2004
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Current Research
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“The future is motion” - Varian annual report 2003
Even when patients are placed in precisely the same position for
their daily treatments, some tumors can shift by as much as two
to three centimeters over six to eight weeks of therapy. In
addition, normal physiological processes like breathing cause
some organs and tumors to move significantly during a daily
treatment session.
As we understand more about tumor
motion, we have had to realize that we cannot position patients
just on the basis of marks or tattoos on their external anatomy. As
the treatments have become more conformal, and as we try to
confine the high dose area much more strictly just to where the
tumor is, we have to be all the more diligent in knowing exactly
where the tumor is, every day.
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MAESTRO WP1.3 - Dynamic RT
• Objective
– To compensate for intra-fraction organ motion by dynamically
shaping the beam in real-time (UEA + UCLM).
Currently researchers
are able to track
implanted gold
markers
© Harvard Medical School
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Portal Video: Respiratory Motion
WP1.3 Aims
to infer
motion
without using
markers
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Ultimately we hope to simulate
Dynamic MLC Control
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ASM: Motion Tracking
© Yu Su , School of Computing Sciences, UEA
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Building & Fitting ASM Models
© Yanong Zhu, School of Computing Sciences, UEA
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Image Registration via Graph Matching
© Muhannad Al-Hasan, School of Computing Sciences, UEA
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Conclusions
• Several Studies have shown IMRT improves quality of RT
– IMRT showed a 92 percent three-year survival rate for early stage prostate
patients and a better than 80 percent three-year survival rate for those
with an initially unfavorable prognosis.
• Set-up error and organ motion interferes with the accuracy
of radiotherapy,
– The important goal of shrinking the treatment margin can only be
achieved with better patient positioning techniques.
• Improvements in electronic portal image devices are needed
before widespread use of Dynamic Image Guided RT is
possible
– WP1.3 should demonstrate it is feasible in a limited number of cases
• e.g Lung
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Acknowledgements
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Alison Vinall - Head of Radiotherapy Physics, NNUH
Dr. Yu Su, Computing Sciences, UEA
Yanong Zhu, Computing Sciences UEA
Muhannad Al-Hasan, Computing Sciences, UEA
MAESTRO
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