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Introduction. What is radiation therapy (RT)?. Cancer treatment Tumor versus normal tissues External photon beam RT. Intensity-modulated RT (IMRT). Brahme et al. 1982 Fluence-modulated beams Homogeneous, concave dose distributions

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what is radiation therapy rt
What is radiation therapy (RT)?
  • Cancer treatment
  • Tumor versus normal tissues
  • External photon beam RT
intensity modulated rt imrt
Intensity-modulated RT (IMRT)
  • Brahme et al. 1982
    • Fluence-modulated beams
    • Homogeneous, concave dose distributions
  • Better target dose conformity and/or better sparing of organs at risk (OARs)
biological imaging
Biological imaging
  • PET
  • SPECT
  • fMRI
  • MRSI

Brain

Tumor

tumor biology characterization
Tumor biology characterization

Apisarnthanarax and Chao 2005

biological imaging for rt
Biological imaging for RT
  • Improvement of diagnostic and staging accuracy
  • Guidance of target volume definition and dose prescription
  • Evaluation of therapeutic response
target volume definition
Target volume definition
  • Gross tumor volume (GTV)
  • Clinical target volume (CTV)
  • Planning target volume (PTV)
dose painting by numbers1
Dose painting by numbers

Biologically Conformal Radiation Therapy

dose calculation algorithms
Dose calculation algorithms
  • Speed versus accuracy:
    • Broad beam
    • Pencil beam (PB)
    • Convolution/superposition (CS)
    • Monte Carlo (MC)
  • Monte Carlo dose engine MCDE Reynaert et al. 2004

Accuracy ↑

Speed ↓

mc dose calculation accuracy
MC dose calculation accuracy
  • Cross section data
  • Treatment beam modeling
  • Patient modeling
    • CT conversion
    • Electron disequilibrium
    • Conversion of dose to medium to dose to water
  • Statistical uncertainties
implementation of bcrt relationship between signal intensity and radiation dose

Dose

Dhigh

Dlow

Signal intensity

Ilow

Ihigh

Implementation of BCRT:Relationship between signal intensity and radiation dose
implementation of bcrt biology based segmentation tool
Implementation of BCRT:Biology-based segmentation tool
  • 2D segmentation grid in template beam’s eye view
    • Projection of targets (+)
    • Integration of signal intensities along rayline (+)
    • Projection of organs at risk (-)
    • Distance
  • Segment contours from iso-value lines of segmentation grid
implementation of bcrt objective function
Implementation of BCRT:Objective function
  • Optimization of segment weights and shapes (leaf positions)
  • Expression of planning goals
  • Biological:
    • Tumor control probability (TCP)
    • Normal tissue complication probability (NTCP)
  • Physical:
    • Dose prescription
implementation of bcrt example
Implementation of BCRT:Example
  • [18F]FDG-PET guided BCRT for oropharyngeal cancer
  • PTV dose prescription:
implementation of bcrt conclusions
Implementation of BCRT:Conclusions
  • Technical solution
    • Biology-based segmentation tool
    • Objective function
  • Feasibility
    • Planning constraints OK
    • Best biological conformity for the lowest level of dose escalation
bcrt planning study set up
BCRT planning study:Set-up
  • BCRT or dose painting-by-numbers (“voxel intensity-based IMRT”) versus dose painting (“contour-based IMRT”)
  • 15 head and neck cancer patients
  • Comparison of clinically relevant dose-volume characteristics
    • Between “cb250” and “vib216-250”
    • Between “vib216-250” and “vib216-300”
bcrt planning study conclusions
BCRT planning study:Conclusions
  • BCRT did not compromise the planning constraints for the OARs
  • Best biological conformity was obtained for the lowest level of dose escalation
  • Compared to dose painting by contours, improved target dose coverage was achieved using BCRT
mc dose calculations in the clinic
MC dose calculations in the clinic
  • Comparison of PB, CS and MCDE for lung IMRT
  • Comparison of 6 MV and 18 MV photons for lung IMRT
  • Conversion of CT numbers into tissue parameters: a multi-centre study
  • Evaluation of uncertainty-based stopping criteria
  • Feasibility of MC-based IMRT optimization
ct conversion multi centre study
CT conversion: multi-centre study
  • Stoichiometric calibration
  • Dosimetrically equivalent tissue subsets
  • Gammex RMI 465 tissue calibration phantom
  • Patient dose calculations
  • Conversion of dose to medium to dose to water
ct conversion conclusions
CT conversion: conclusions
  • Accuracy of MC patient dose calculations
  • Proposed CT conversion scheme:

Air, lung, adipose, muscle, 10 bone bins

  • Validated on phantoms
  • Patient study:

Multiple bone bins necessary if dose is converted to dose to water

biologically conformal rt
Biologically conformal RT
  • Technical solution
    • Bound-constrained linear model
    • Treatment plan optimization
      • Biology-based segmentation tool
      • Objective function
    • Treatment plan evaluation
  • Feasibility of FDG-PET guided BCRT for head and neck cancer
mc dose calculations
MC dose calculations
  • Individual patients may benefit from highly accurate MC dose calculations
  • Improvement of MCDE
    • CT conversion
    • Uncertainty-based stopping criteria
  • Feasibility of MC-based IMRT optimization
  • MCDE is unsuitable for routine clinical use, but represents an excellent benchmarking tool
adaptive rt inter fraction tumor tracking
Adaptive RT:Inter-fraction tumor tracking
  • Anatomical & biological changes during RT
  • Re-imaging and re-planning
  • Ghent University Hospital: phase I trial on adaptive FDG-PET guided BCRT in head and neck cancer
summation of dvhs
Summation of DVHs

Dose 1

CT 2

Dose 2

CT 1

Registration

Structure 1

Structure 2

Points

TPoints

P Doses

TP Doses

Total

DVH

Total doses

summation of qvhs
Summation of QVHs

PET 1

Dose 1

PET 2

CT 2

Dose 2

CT 1

Registration

Registration

Registration

Structure 1

Structure 2

Points

TPoints

Disregard TPoints

outside structure 2

P Q-values

TP Q-values

Total

QVH

Total Q-values

slide48

Fundamental research in vitro, animal studies

Radiobiology

  • Biological imaging
  • Tracers
  • Acquisition, reconstruction, quantification
  • Treatment planning and delivery
  • Biological optimisation
  • Adaptive RT

Treatment outcome

Nuclear medicine

Radiotherapy physics

Radiotherapy

Clinical investigations

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