Radiotherapy is one of the therapeutic weapons with the surgery of local cancer treatment. Radiation therapy involves exposing part of the body to ionizing radiation. The principle of ionizing radiation is to deliver a certain amount of energy, the importance of which alters the DNA of cells without directly killing them. The cells will die afterwards, when they need their DNA. These methods are not specific to cancer cells but they are more sensitive than healthy cells.

Complex radiotherapy techniques, such as stereotaxy (a technique based on the use of small converging beams to irradiate very small volumes in the patient’s body at high doses), require high precision in their implementation. These techniques require accurate treatment verification to estimate the radiation dose absorbed by the patient before and during treatment (in vivo dosimetry).

The portal imaging system or E.P.I.D. for Electronic Portal Imaging Device is a system positioned under the radiotherapy treatment table, allowing an image of the iradiation field to be captured via the radiation sent to the tumour (as a simple X-ray would do). It therefore allows imaging to perform a “live” control of the patient’s position during treatment as well as measurement of the delivered radiation .

Currently, the EPID offers an attractive solution, especially  to perform in vivo dosimetry. However, the implementation of in vivo dosimetry, and in 3D, of complex treatments is still limited, if not impossible.

In this work, published in the journal Phys Med, team 15 «Multi-resolution dosimetry for the optimization of radiotherapy» of the CRCT associated with the Department of Engineering and Medical Physics of the IUCT-oncopole evaluated the response characteristics of an EPID imager under complex conditions that may be present in stereotactic radiotherapy.

This work thus facilitates the development of a more complete dosimetric model, in 3D and in vivo, for a verification adapted to complex treatments, before, and especially, during the treatment of the patient. This model has already been developed and applied to stereotactic treatments, offering very satisfactory and promising results. Once fully validated, it will also allow the evaluation of the dosimetric commercial solutions currently available.

Discover the published article :

Phys Med. 2020 Sep 24;78:117-122.
Dosimetric performance of continuous EPID imaging in stereotactic treatment conditions
Ana Rita Barbeiro, Laure Parent, Laure Vieillevigne, Regis Ferrand, Xavier Franceries

Key words :

• EPID Dosimetry;
• EPID Response;
• Portal Imaging;
• Stereotactic Radiotherapy Verification.

Contact :

Ana Rita Barbeiro
Team 15 – Multiscale dosimetry for radiotherapy optimization.
Mail : pbanarita@gmail.com

Collaborations :

IUCT-Oncopole (Medical Physics and Engineering Department).

One picture :

Figure 1. Results of the assessment of linearity of EPID response in continuous mode with rotational fields. This showed a linearity of response independent of dose rate variations. (a) Relative EPID response per monitor unit (UM), all points are normalized to 500 MU. (b) Angular UM distributions per frame corresponding to two arc lengths of the 6 MV FFF beam.