Radiation therapy must take into account tumor motion. Indeed, during the treatment the target can move up to several centimeters. This could lead to an under dosage of the target or an over dosage of the Organs at Risk (OARs). For classic treamtment the motion is taken into account by using a saftey margins. But when the intensity is modulated (the target is irradiated progressively with a moving collimator to be more conformal) there is an additional risk to combinate badly the tumor motion and the motion of the collimator leaves (interplay effect). This work assessed this Interplay Effect for different clinical configurations using the computation reference method (Monte-Carlo). The conclusion is that the Interplay Effect is negligible for clinical conditions (more than 3 fractions, and more than 20 breathing cycles)

This work was done before starting the stereotactic treatment of lung cancer. Based on these results, the treatment is now achieved using intensity modulation.

A personalized tool could be proposed to foresee the Interplay Effect for each patient.

Discover the published article :

Phys Med. 2021 Jun 10;87:73-82. doi: 10.1016/j.ejmp.2021.05.019. Online ahead of print.
A study of the interplay effect in radiation therapy using a Monte-Carlo model.
Leste J, Medjahed I, Chauvin M, Younes T, Vieillevigne L, Ferrand R, Franceries X, Bardies M, Simon L.

Key Words :

  • Interplay ;
  • Monte-Carlo ;
  • Radiotherapy ;
  • lung cancer

Collaborations and acknowledgements

This work was granted access to the HPC resources of CALMIP supercomputing center under the allocation 2016-P19001.

Contact :

Luc SIMON
Team CRCT  : RADOPT : Optimization of radiotherapy: from mechanisms to clinical trials
Mail : simon.luc@iuct-oncopole.fr

One picture

Dose profile in the direction of tumour movement, through the tumour (CTV)

The broadest profile corresponds to a classical clinical calculation, based on a static image of the tumour. The other dose profiles are made by simulating the movement and observing the different effects (collapse of the profile slopes or blurring effect and interplay effect on the plateau).