Prompt gamma-ray imaging of nanoparticles for in vivo range verification in proton therapy

Proton therapy is an emerging modality for cancer treatment that induces a better dose con- formation, compared to traditional photon radiotherapy. In vivo range verification techniques are required to fully exploit the advantages of proton therapy. In the past few years, the use of nanoparticles as dose enhancers has increased due to their potential amplifying the ra- diation induced damage. This thesis studies the combination of both techniques, as it will generate a dose enhancement, while verifying the range of the protons with the detection of the characteristic prompt gamma-rays emitted by the nanoparticles.

To investigate the feasibility of performing prompt gamma-ray imaging using characteristic gamma rays from nanoparticles, a magnetite (Fe3O4) target was developed in house, consisting of a solution of nanoparticles diluted in water. The detection system consists of two different types of detectors: a CLLB scintillator and a hyper-pure germanium semiconductor.

In-beam measurements were performed at the University of Birmingham (UK) and KVI- CART (Netherlands) at three different beam energies. In the current work, it is found that the CLLB detector allows for the distinction of different target compositions using the coarse energy regions in the prompt gamma-ray spectrum. The HPGe detector allows to resolve many more characteristic prompt gamma-rays with a much higher peak-to-background ratio, compared to the scintillator detector, and obtain their intensity profile.

The results presented suggest that the combination of both methods provides a viable way to determine the range of the protons and confirm the location of the tumour area. The present work also indicates that measuring gamma-ray yields, using a treatment dose and nanoparticle concentration similar to the ones applied in clinic, are sufficient for localising the intensity profile of the characteristic gamma rays from the nanoparticles with a precision of a few mm, hence providing an additional tool for in-vivo range verification.