CAPPERAM · Contrast Agents for Protontherapy PET Range Monitoring

Contrast Agents for Protontherapy PET Range Monitoring

Particle therapy is an innovative mode of external radiotherapy that utilizes the favourable ballistic properties of protons and carbon ions (vs. photons and electrons) to deliver more conformal dose distributions in the patients, maximizing doses to the target volumes whilst minimizing risks to surrounding healthy tissues. In radiation therapy, proton therapy has a more favourable dose distribution than conventional radiotherapy with photons and electrons. However, in order to fully exploit this dosimetric advantage, it would be required to verify the range of protons in the patient with mm accuracy. The most used strategy for in-vivo range verification in protontherapy relies on positron emission tomography (PET) activation. As they progress through the patient, proton beams undergo nuclear reactions that can produce radioactive isotopes, some of which are positron-emitters. This induced radioactivity can be detected in commercial or dedicated PET scanners and used to deduce the delivered dose distribution in the patient. While a promising technique, two main challenges have so far limited its clinical implementation: first, the proton interaction cross sections of the elements making up the body (C, O, N, H) are relatively low, which causes the positron disintegration counts detected by the PET scanners to be about 1 or 2 orders of magnitude lower than the usual numbers in nuclear medicine. And second, the spatial and temporal distributions of PET emitters follow a very complex relation with the dose depositions which complicate the range verification process. The CAPPERAM project aims at solving these two problems by administering contrast agents in patients prior to irradiation. Some elements, such as Zn, have a very high cross section for proton interaction peaking at very low proton energies, which would produce a very high concentration of PET emitters near the end of the proton range. AIMS: 1) Develop a calculation tool that can predict the effect of contrast agents during proton irradiation and identify relevant potential contrast agents. 2) Produce proof-of-principle data using phantoms or animal models to validate the technique. The global aim is to reduce uncertainty margins in proton therapy, increasing its therapeutic window and reducing side effects.

Data: CORDIS, © European Union