Nuclear reaction driven quality assurance in hadrontherapy

Prompt secondary radiations such as gamma rays and protons can be used for real time control of the ion range during ion therapy. We present a review of the ongoing activities by the IPNL-CREATIS collaboration, in terms of detector developments and physical issues concerning the correlation between the physical dose and nuclear reaction processes. - Prompt-gamma imaging: during the irradiation, photons in the range 1-10 MeV are emitted almost isotropically within much less than a picosecond after nuclear reactions. Therefore, a dedicated collimated detection setup may provide real-time information on the location of fragmentation [1]. This can be done with a collimated gamma camera or a Compton camera, provided time of flight is used to discriminate between direct photons and background scattered particles like neutrons. - Proton Interaction Vertex Imaging: during carbon therapy, secondary protons are - more surprisingly - also helpful for real-time determination of the ion range, even for deep-seated tumors where the residual range for protons to escape the patients in forward direction reaches 10 cm. A tracking system with thin silicon pixel detectors is used to image the interactions vertices that are shown to be correlated to the carbon range [2]. - A common beam tagging hodoscope is developed for both applications, where the incident position and the time of each particle (or bunch of particles) need to be identified.It consists of a X,Y scintillating fibers array, read by flat panel photomultipliers and a dedicated fast electronics. - Geant4 simulations are performed to reproduce both the dose profile (including the displaced dose deposited by secondaries) and the emission of secondaries. A proper tuning of the hadronic models was necessary to reproduce satisfactorily the prompt gamma and charged particle yields. Such simulations are also used to design the detection setups described above. References: [1] E. Testa et al., "Dos profile monitoring with carbon ions by means of prompt-gamma measurements", Nuclear Instruments and Methods B 267 (2009) 993 [2] P. Henriquet et al., "Ion-range monitoring during carbon ion therapy by means of interaction vertex imaging (IVI) with secondary protons: a feasibility study", Phys. Med. Biol. 57 (2012) 4665-4669 Work supported by the FP7-ENVISION and ENTERVISION programs, the INCa Quapivi, the ANR Gamhadron, the Rhone-Alpes Regional Program for Hadrontherapy (PRRH), the MI2B GDR and the LabEx PRIMES.