CART Flashcards
Describe the treatment workflow from imaging to treatment
The whole process includes
1) Treatment planning
- physical model through multimodality imaging (image fusion)
- anatomical model (segmentation process)
- treatment design (field shape and geometry)
- collimation, BEV approach
- IMRT through MLC
- Calculation of the fluences is the reverse problem to tomography
- treatment modeling: calculation of the predicted physical dose delivered
- model the interactions of particles with tissues: depth-dose curve
- model the interactions in the treatment machine which can produce scattered
photons or secondary electrons
- calculation of the concrete dose to the patient: analytical approach with density correction or simulative approach with Monte Carlo methods.
2) Treatment evaluation: assessment of the benefits and the quality of the
treatment
- Visual assessment: color wash, isodose curves/surfaces, combinations (PROBLEMS)
- Quantitative method: DVH reduces 3D dose distributions to 1D curve. Biological information are missing.
- There is no optimal plan. The quality depends on the constraints and the priorities.
- PARETO FRONT: models are considered equally good if no objective can be improved without sacrificing another objective.
3) Modeling of the treatment outcome: Achieve clinically relevant predictions through biological models. They convert the physical dose into biologically relevant endpoints:
- Assumptions about the organs architecture
- NTCP or TCP are biological models typically considered: Lymann-Kutcher-Burmann model for NTCP
What is a treatment planning system?
The software used to design and optimize the treatment plan for the patient. Takes the initial planning images and the constraints/priorities as input and generates a plan conformal to the tumor by giving the dose distribution and the optimal treatment geometry.
The output data guides the radiation delivery system.
What is the target in treatment planning? Why is it not equal to the visible tumor?
The target is the PTV, containing GTV, CTV (spread of the microscopic disease), ITV (consider internal motion of the anatomy) and margins to allow set-up variations.
Describe the different treatment modalities
Photon therapy:
- 3D CRT: the beam is shaped with collimators but we don’t modulate intensity
- IMRT: intensity modulated RT
- VMAT: Volumetric modulated arc therapy –> vary gantry speed and aperture to do dose painting, the fluence doesn’t change.
Proton therapy:
- PS: passive scattering
- AS: active scanning
- Arctherapy
What is a MLC and what is it used for?
How does a dose distribution change when using a MLC?
What is the corresponding strategy to deliver intensity modulated RT for hadrontherapy?
Multi-leaf collimator: is a device used to modulate the intensity of the beam and adapt its shape to that of the tumor.
It is made of individual leaves of high-Z material and can be used either in a static, multisegmented or in a dynamical way.
The dose can be painted: higher dose delivered to the PTV and less dose to OAR/healthy surrounding tissues. Dose painting is the prescription of a non-uniform dose distribution to the target volume based on images showing risk of elapse.
In hadrontherapy we can also use MLC, or active scanning.
