[Poster] Optimisation, Verification & Validation of Transit Dosimetry

Mathilde Croisé1, Sofia Celi1, Fabien Lebeaux2, Pascal François1
1 Institut Curie, Medical Physics department, Paris, France
2 IBA Dosimetry, France

Presented at ESTRO 2014

Introduction: In radiotherapy, the complexity of modern treatment techniques requires advanced quality assurance controls. Since 2011, the in vivo dosimetry (IVD) verification is mandatory in France. It consists of a measurement during the patient treatment to control if the delivered dose is in line with the planned dose.
Several methods are used to performed IVD:

  • detectors (diode, thermoluminescent dosimeter, mosfet): the delivered dose inside the patient is the average of the dose picked up by two detectors
    fixed on the patient skin, at the input and the output of the beam.
  • transit dosimetry: the delivered dose inside the patient is a mathematic reconstruction of the dose transmitted on a electronic portal imaging device (EPID) embedded on the linear accelerator.

In volumetric modulated arc therapy technique (RapidArc), a systematic discrepancy of about -3% is observed between the transit dose and the planned dose. The goal is to investigate the source of this discrepancy while checking both doses with the help of several softwares and detectors.