Imaging - Fundación Marie Curie

Aspectos fisicos de SRS
Intra craneal y SBRT en
Columna
Aluísio Castro
Físico Médico Especialista em Radioterapia
Centro de Oncologia D´Or - Rio de Janeiro - Brasil
Agenda
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Patient Immobilization
Imaging
Treatment Planning
Patient/Target Localization
Treatment Delivery
QA
P.S. Focus on Exactrac System
Patient Immobilization
Cranial
• Invasive Frame based
– Rigid
– Invasive
– No fractionation allowed
• Frameless systems
– Mask system
– Allows some interfraction differences
– Image guided patient localization
Patient Immobilization
Spine
• Invasive Frame based
– Invasive
– No fractionation allowed
• Noninvasive body frame
– Lack of rigid fixation to vertebral column
Patient Immobilization
Spine
• Frameless systems
– Image guided target localization
– Monitoring for patient movement
– Customized cradle and vacuum bag
• Some immobilization
• Patient stabilization
• Patient confort
– Mask systems
• Cervical and upper thoracic (T1-T3)
Imaging
• Imaging Modalities
– CT is mandatory for treatment planning
• Geometric target localization
• Electron density information for heterogeneity
correction during UM calculation
• Slices < 3mm for DRR accuracy
– MRI is essential for a good target delineation
• Soft tissue contrast
• High spatial resolution is required (<1mm slice)
Imaging: Registration MRI x CT
Imaging: Registration
• Volume of interest
Imaging: Registration
• Volume of interest
Imaging: Registration
• Volume of interest
Imaging: Registration
• Volume of interest
Imaging
• Registration issues
– Artifacts
– Body articulation
Tretatment Planning
• Aims:
– Comform radiation dose to the target
– Rapid dose fall-off
– OAR sparing
• Large number of beams (static techniques)
– Conformal or IMRT
• Volumetric techniques
– Hybric Arc, RadipArc, VMAT
Tretatment Planning
• Dose calculation algorithms:
– Pencil Beam works fine in homogeneous regions like
brains but tends to overstimate target coverage in
presence of inhomogeneities
– MC is the algorithm of choice for areas with density
heterogeneity as spine surroundings
Tretatment Planning
• Dose calculation algorithms:
– Pencil Beam works fine in homogeneous regions like
brains but tends to overstimate target coverage in
presence of inhomogeneities
– MC is the algorithm of choice for areas with density
heterogeneity as spine surroundings
Localization
• 2D Radiography
– EPID (MV)
– KV (machine-mounted or room-mounted)
– Bony anatomy
• CBCT (MV or KV)
– Bony and soft tissue anatomy
– Not allowed with couch ≠ 0º.
Localization
• Bony anatomy
• Soft tissue
• Fiducials
Localization
• Bony anatomy
• Fiducials
• Neighbor-vertebra trick
Localization
• Bony anatomy
• Fiducials
• Neighbor-vertebra trick
Localization tricks – 2D images
Localization tricks – 2D images
Exactrac – Infra Vermelho (IR)
Exactrac – Infra Vermelho (IR)
• Fonte de luz IR
• Refletores IR fixos ao
paciente
• Duas câmeras IR
• Posicionamento inicial do
paciente
• Monitoramento real-time do
posicionamento
Exactrac – Raios X (RX)
• 2 tubos de RX
• 2 detectores Flat Panel
• Fusão com imagens de
planejamento (DRRs)
• Cálculo do deslocamento
translacional e rotacional
do paciente
Exactrac – Mesa Robótica 6D
• Movimentos de
translação (lat., vert.,
long.) e rotação (pitch,
roll e table)
• Precisão
submilimétrica e
décimos de grau
Quality assurance
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Patient specific
Laser aligment
Winstow-Lutz test
Image Guidance Device Test
Dosimetric tests
Machine QA
Quality assurance
• Laser aligment to radiation isocenter
Winston-Lutz Test
Quality assurance
• Laser and imaging isocenter aligment
Quality assurance
• InfraRed System calibration
Quality assurance
• RX System calibration
Quality assurance - Other tests
• Image Quality
– Detector gain, dead pixel correction
– X-ray generator performance
• Gantry, collimator and couch isocenter
• Dosimetric tests
– Beam symmetry and flatness, PDDs, OFs
• MLC
• Beam calibration
Quality assurance - Processes
• Double check:
– Image labels (name, id, etc...)
– Target delineation, dose prescription (second
opnion)
– Planning (DVHs, MUs, dose distribution,
collision risks, etc...)
– Printouts, export and import of files, OIS
– Treatment delivery (patient movements and
machine performance)
Summary
• Patient Immobilization
• Imaging and Target & OAR delineation
– proper modality and registration
• Planning
– multiple fields / volumetric techniques
– attention to the OAR limits of dose
• Patient localization
– image guidance
• Delivery
• QA systems and processes
Gracias!
[email protected]