CART

Question 1

Describe the treatment workflow from imaging to treatment

Answer 1

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

Question 2

What is a treatment planning system?

Answer 2

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.

Question 3

What is the target in treatment planning? Why is it not equal to the visible tumor?

Answer 3

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.

Question 4

Describe the different treatment modalities

Answer 4

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

Question 5

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?

Answer 5

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.