First tests of the prompt gamma ray timing method at a clinical proton accelerator

The characteristic dose profile of accelerated ions has opened up new horizons in the context of cancer treatment. However, particle range uncertainties strongly constrain the potentialities of ion beam therapy. Despite of worldwide efforts, a detector system for range and dose delivery assessment in real-time is not yet available for clinical routine.
Complementary to the active- and passively collimated prompt gamma ray imaging systems for range assessment, the prompt gamma ray timing method has been recently proposed and tested at a research accelerator. Based on the measurable transit time of ions through matter, the emission times of prompt gamma rays encode essential information about the depth-dose profile.
In a collaboration between OncoRay, Helmholtz-Zentrum Dresden-Rossendorf and IBA, the prompt gamma ray timing method was tested for the first time at a clinical proton accelerator (Westdeutsches Protonentherapiezentrum Essen) with different phantoms. Several fast scintillation detectors were used to acquire prompt gamma ray timing distributions at various geometries and proton energies.
From the resulting distributions, particle range differences of around 5 millimetres in heterogeneous phantoms were observed by simple qualitative inspection. In conclusion, our preliminary analysis points out that the prompt gamma ray timing method for range verification is feasible in a clinical radiation environment and realistic phantoms, which reassures this novel approach as a promising alternative in the field of prompt gamma based in vivo dosimetry.