Particle therapy offers finite penetration depth, low energy deposition at the entrance and sharp dose fall-off. However, some of its benefits may become a risk for the patient due to unexpected uncertainties in the delivery of the dose.

Real time beam delivery control is of key importance in order to improve targeting accuracy and an accurate measurement of the beam energy is of paramount importance.

At the state of art particle beam energy is tuned at the extraction from the accelerator and checked only during routine QA procedures.

DE.TEC.TOR. is working on a system for on-line measuring the therapeutic particle beam energy. It will be based on the coupling of a fast silicon-based particle counter and a typical ionization chamber housed on the beam nozzle to control the treatment.



The particle counter is a layer of advanced silicon detector, segmented into pixels and able to discriminate consecutive particles in order to count their number in a given time interval.


The ionization chamber arranged downstream collects the total deposited charge by the particle beam so that the correlation of such information allows retrieving the particle stopping power and therefore its energy.

In order to have a maximum error in range estimation <1 mm the requested precision in the determination of particle number is <1% . Moreover for a typical beam flux of 109 particles cm-2 sec-1 the needed time resolution to discriminate and count is <1 ns.

For such purpose dedicated Ultra Fast Silicon Detectors (UFSD) are currently under development by the INFN-Turin in collaboration with FBK in Trento [1]. Such UFSD are based on Low-Gain Avalanche Detectors (LGAD) technology optimized for timing [2]. The main features are a small active volume (thickness of ~ 50 um) that leads to a very short signal (1,5-2 ns) and a low gain layer implanted under the cathode to obtain enhanced signals and so excellent time resolution (tens of ps).

[1] Vignati, A. et al., (2017). Innovative thin Silicon detectors for monitoring of therapeutic proton beams: preliminary beam tests, JINST 12 C12056

[2] Sadrozinski, H. et al., (2018). 4-Dimensional tracking with Ultra-Fast Silicon Detectors, Reports on Progress in Physics 81, 026101


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