Medical Imaging

Proton radiography to reduce range uncertainty in proton therapy

ImagX.R, the research group on image guided proton therapy, has the pleasure to announce the PhD defence of Sylvain Deffet. He will present his research on proton radiography and discuss how this method could improve treatment outcome in proton therapy.

Proton therapy is an advanced form of radiation therapy which is increasingly used worldwide. Unlike photons, protons deliver a sharp dose at a precise location corresponding to their range in the patient. Thanks to this physical property, proton therapy has the potential to spare healthy tissues better than conventional radiation therapy. However, a consequence of this dosimetric property is that the range of the protons inside the patient must be accurately predicted to deliver the dose as planned. Unfortunately, several uncertainties arising during treatment planning may significantly impact the range of the protons and hence jeopardize dose conformity. To better quantify and potentially reduce the uncertainties, the implementation of imaging techniques that would provide a direct information on the energy reduction of protons in the patient is highly desirable. In the present thesis, such a method is introduced: proton radiography. The system that we propose relies on the use of protons having an energy high enough for them to traverse the patient and stop inside a detector which measures their residual range. By comparing measured and predicted residual ranges, it is possible to quantify range uncertainties in the patient in clinical conditions.

Although the principle of proton radiography is relatively straightforward, a clinical implementation of such a measurement device is a complex issue. This thesis aims at developing a proton radiography system and also at conceiving an acquisition process that could be conveniently implemented in clinics. The methodologies to correctly take advantage of proton radiography measurements are also discussed, in order to further optimize the dose delivered to the patient and improve de facto the treatment outcome.