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Three-Dimensional
Conformal
Radiation Therapy
Chapter 8
Perez 2008
Presented by :Dr .M .Dorchin
• Modern anatomic imaging technologies, such
as x-ray computed tomography (CT) and
magnetic resonance imaging (MRI) provide a
fully three-dimensional model of the cancer
patient's anatomy, which is often
complemented with functional imaging, such
as positron emission tomography (PET) or
magnetic resonance spectroscopy.
• Such advanced imaging now allows the radiation
oncologist to more accurately identify tumor volumes
and their relationship with other critical normal
organs.
• Powerful x-ray CT-simulation and three-dimensional
treatment planning systems (3DTPS) have been
commercially available since the early 1990's and threedimensional conformal radiation therapy (3DCRT) is now
firmly in place as the standard of practice.
• In addition, advances in radiation treatmentdelivery technology continue and medical
linear accelerators now come accurately with
sophisticated computer-controlled multileaf
collimator systems (MLCs) and integrated
volumetric imaging systems that provide beam
aperture and/or beam-intensity modulation
capabilities that allow precise shaping and
positioning of the patient's dose distributions .
• Conformal treatment plans generally use an
increased number of radiation beams that are
shaped to conform to the target volume.
• To improve the conformality of the dose
distribution, conventional beam modifiers
(e.g., wedges, partial transmission blocks,
and/or compensating filters) are sometimes
used.
• This chapter will review the critical
components that make up the conformal
therapy planning and delivery process,
focusing mainly on the forward-planned
3DCRT process.
Historical Development of Conformal Therapy
and 3-D Treatment-Planning Systems
• Conformational treatment
methods were pioneered in
the 1950s and 1960s by
several groups, including
Takahashi in Japan, Proimos ,
Wright et al., and Trump et al.
in the United States; and
Green et al. in Great Britain.
• This work continued into
the 1970s, when several
groups actually
implemented computercontrolled radiation
therapy, including the
Joint Center in Boston
project led by Bjarngard et
al. and Kijewski et al. ,
and the Tracking Cobalt
Project led by Davy et al.
at the Royal Free Hospital
in London.
• Sterling et al. are credited with the first
3D approach (dose calculation and
display) to treatment planning.
National Cancer Institute Research Contracts in
Support of Three-Dimensional Radiation Therapy
Treatment Planning
•1- Evaluation of Treatment Planning for Heavy Particles (1982–1986)
University of Pennsylvania School of Medicine and Fox Chase Cancer Center
•Lawrence Berkeley Laboratory and University of California
•Massachusetts General Hospital
•M.D. Anderson Cancer Center - University of Texas
•2- Evaluation of Treatment Planning for External-Beam Photons (1984–1987)
University of Pennsylvania School of Medicine and Fox Chase Cancer Center
•Memorial Sloan-Kettering Cancer Center
•Massachusetts General Hospital
•3- Washington University in St. Louis
Evaluation of Treatment Planning for External-Beam Electrons (1986–1989)
University of Michigan
•M.D. Anderson Cancer Center - University of Texas
•Washington University in St. Louis
•4- Development of Radiation Therapy Treatment Planning Software Tools (1989–1994)
University of North Carolina
•University of Washington
•Washington University in St. Louis
• In the 1990s, the commercial availability of
3DTPSs led to widespread adoption of 3D
planning and conformal therapy as the
standard of practice.
• One of the keys to this development was a
series of research contracts funded by the
National Cancer Institute (NCI) in the 1980s
and 1990s to evaluate the potential of 3D
planning and to make recommendations to
the NCI for future research in this area.
Three-Dimensional
Treatment Planning
• Forward-based 3D planning for conformal
therapy typically involves a series of
procedures summarized in Table 8.2
• These include establishing the patient's treatment
position (including constructing a patient
repositioning immobilization device when
needed), obtaining a volumetric image dataset of
the patient in treatment position, contouring target
volume(s) and critical normal organs using the
volumetric planning image dataset, determining
beam orientation and designing beam-block
apertures or MLC leaf settings, computing a 3D
dose distribution according to the dose
prescription, evaluating the treatment plan, and, if
needed, modifying the plan (e.g., beam
orientations, apertures, weights, modifiers) until
an acceptable plan is approved by the radiation
oncologist.
Table 8.2
Three-Dimensional Treatment
Planning Process
Step 1:Patient positioning and immobilization
*Construct patient repositioning/immobilization
device
*Establish patient reference marks/patient
coordinate system
Step 2: Image acquisition and input
*Acquire/input CT (MR or other imaging data)
into three-dimensional radiation therapy
treatment planning system.
Step 3: Anatomy definition
*Geometrically register all input data (such as CT, MR)
*Define and display contours and surfaces for organs at
risk
*Define and display contours and surfaces for target
volumes
*Generate electron density representation from CT or
from assigned bulk density information
Step 4: Dose prescription
*Specify dose prescription for planning target
volume(s)
*Specify dose tolerances for organs at risk
Step 5: Beam technique
*Determine beam
arrangements (beam's-eyeview and room's-eye-view
displays) ?
*Design field shape (blocks,
multileaf collimator leaf
settings)
*Determine beam modifiers
(compensators, wedges,
partial transmission blocks)
*Determine beam weighting
Step 6: Dose calculations
*Select dose-calculation algorithm
and calculation grid
*Input dose prescription
*Perform dose calculations
*Set relative and absolute dose
normalizations
Step 7: Plan evaluation/improvement
*Generate two- and threedimensional isodose displays
*Generate dose & volume
histograms
*Perform visual DVH and
isodose comparisons
*Use automated optimization
tools if available
*Modify plan based on
evaluation of the dose
distribution
Step 8: Plan review and documentation
*Perform overall review of all aspects of plan
and obtain physician approval
*Generate hard copy output including digitally
reconstructed radiographs
Step 9: Plan implementation and verification
*Transfer plan parameters into treatment machine
record-and-verify system
*Set up (register) the real patient according to
plan (verification simulation optional)
*Perform patient treatment quality assurance checks
including independent check of monitor units.
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