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M. Saiful Huq – Transition from 2D to 3DCRT & IMRT 1 IAEA-CN-170/013
Implementing 3D conformal radiotherapy and IMRT Implementing 3D conformal radiotherapy and IMRT in clinical practice: Recommendations of IAEAin clinical practice: Recommendations of IAEA--
TECDOCTECDOC--15881588
M. Saiful Huq, Ph.D., Professor and Director, Dept. of Radiation
OncologyUniversity of Pittsburgh Cancer Institute, Pittsburgh, Pennsylvania, USA
ICARO Vienna April 27-29 2009
Goal of radiation therapyGoal of radiation therapy
•
Conformity of dose distribution to a 3D target volume at the same time minimizing the dose to an acceptable level to the surrounding healthy structures
•
Achieve local (or regional) control with limited risk of normal tissue complications
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Conventional radiation therapyConventional radiation therapyShaped field defined from planar radiograph
3D conformal radiation therapy3D conformal radiation therapy
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Full 3D CT dataset; ICRU 50,62 definition of target and OAR volumes
IMRT IMRT
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Full 3D CT dataset; ICRU 50,62 definition of target and OAR volumes; co-registration of PET and CT images
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IMRT IMRT (3DCRT) (3DCRT) planning and delivery planning and delivery
processprocess
Positioning and immobilization
Image acquisition
Structure segmentation
Treatment planning and evaluation
File transfer and management
Plan validation as necessaryTreatment delivery and verification
Position verification
Adapted from an illustration presented by Webb, 1996
IMRTIMRT
Requires knowledge and understanding of•
patient immobilization/organ motion
•
volumetric imaging•
3D heterogeneous dose calculations
•
large-scale optimization•
dynamic beam delivery of non-uniform beam fluences
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IMRT IMRT --
advantagesadvantages
•
Highly conformal, even concave dose distributions
•
Large dose gradient near the perimeter of both the target volume and healthy structures
Potentially allows for AHARA [as high (dose) as reasonably achievable]Decreased dose to normal tissue
•
Improvement of therapeutic ratio
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HoweverHowever……
•
Increased conformity of IMRT may lead to “geographical miss of the tumor”
due to inadequate
target delineation, organ motion, patient positioning inaccuracies
•
A larger margin may lead to unacceptable high dose to adjacent normal critical structures
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Clinical implementation of IMRTClinical implementation of IMRT
•
Equipment and space requirements•
Staff training and patient education
•
Time and personnel requirements including their responsibilities
•
Changes in treatment planning & delivery practices•
QA of equipment and individual patient treatments
•
Changes in scheduling & overall integration
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See also: IAEA TECDOC 1588 AAPM Guidance document: Med Phys 30, 2089-2115 (2003)
Clinical implementation of IMRT: Highlights Clinical implementation of IMRT: Highlights
• Linac •
MLC
•
OBI/CBCT•
Gating
• Shielding• Imaging
•
CT Sim
(MRI, PET/CT)•
EPID, port films
•
4D CT (optional)
• TPS•
Inverse planning
•
R&V•
2nd
check software
• Immobilization• QA/Dosimetry
•
Chamber/diode array or film/EPID dosimetry
•
MLC QA (film/EPID)
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EquipmentEquipment
Physicians•
Cross-sectional anatomy
•
Inverse planning concepts, dose constraints•
Margins, effects of organ motion
•
DVH based planning and analysis•
Plan evaluation-dose conformality/heterogeneity
•
Dose prescription•
Limitations of IMRT
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Clinical implementation of IMRT: HighlightsClinical implementation of IMRT: Highlights
See also: IAEA TECDOC 1588 AAPM Guidance document: Med Phys 30, 2089-2115 (2003)
TrainingTraining
Medical physicists
•
Understanding of optimization methods•
Characteristics of IMRT dose distributions, plan QA
•
Beam modeling and delivery for IMRT
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See also: IAEA TECDOC 1588 AAPM Guidance document: Med Phys 30, 2089-2115 (2003)
Clinical implementation of IMRT: HighlightsClinical implementation of IMRT: Highlights
TrainingTraining
In addition to the previous ones
Medical oncologist•
IMRT/SRS/SBRT
Radiologists•
PET
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Additional StaffingAdditional Staffing
•
Increased time for planning and delineation of target volume (Physician, planner)
• Image guidance•
Increased treatment time/delivery/QA
Clinical implementation of IMRT: HighlightsClinical implementation of IMRT: Highlights
TrainingTraining
TUMOUR STAGINGTUMOUR STAGING
WITH PET (WITH PET (1818FF--FDG)FDG)
Self questions to be asked!!Self questions to be asked!!
•
What can be achieved with IMRT?•
What specific dose goals should be given to specific treatment sites?
•
What are the dose/dose-volume tolerances of organs at risk?
How is this affected by fractionation?•
How are achievable results affected by margins-
immobilization, localization, treatment delivery method, TPS and dose calculation method?
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Modern radiotherapy is complexModern radiotherapy is complex
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Hardware breaks, software always has bugs, and people Hardware breaks, software always has bugs, and people make mistakes!make mistakes!
Every clinic is susceptible to these kinds of errors Every clinic is susceptible to these kinds of errors (i.e., BIG ones) !(i.e., BIG ones) !
Reported accidental exposures with new Reported accidental exposures with new technologies technologies
•
Keeping equipment in calibration is essential•
Few events resulted from machine errors
Micro-multileaf collimatorVARiS IMRT/MLC
•
However, each had a strong human failure•
The vast majority of events begin with a staff error
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IAEA-CN-170/013
ROSIS database; ICRP Draft 2009
M. Saiful Huq – Transition from 2D to 3DCRT & IMRT18 IAEA-CN-170/013 Josef Novotny
Assessment of doseAssessment of dose
ICRP draft 2009ICRP draft 2009
Risk-informed and cost-effective approaches for prioritizing tests and checks by means of prospective methods of risk assessment, to be performed in cooperation with manufacturers
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•
What is Risk?A term which frequently embodies
probability of an event occurring and severity should such an event occur
•
Need to quantitate
probability and severity
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Risk assessmentRisk assessment
AAPM TG100: A new paradigm for QA in radiation therapy
•
New toolsProcess treeFMEAFault tree
ConclusionsConclusions
•
Human factorsTrainingMiscommunication within and between departments
•
Lack of attention by people performing task•
Lack of consistent procedural guidelines
•
People as well as linacs, need to be “commissioned”•
Lack of comprehensive QA, QC & QM programs
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AAPM TG100: A new paradigm for QA in radiation therapy
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It is useful to report all accidents before consequences appear
Our job is not to prevent errors, but to
keep the errors from injuring the patients.
Lucian Leape
It is impossible to make anything foolproof because fools are so ingenious.
Artur Bloch,
Murphy’s law
Courtesy: Josef Novotny