A circuit arrangement for acquisition of signals from an apparatus for measuring beams of charged particles for external radiotherapy, in particular protons, carbon ions, and other ion species, emitted by particle accelerators, comprising at least one ionization-chamber sensor (10), which includes a plurality of sensor channels (20), said circuit arrangement (200; 500) comprising a plurality of channel branches (B0, . . . , B63; BR0, . . . , BR63) in parallel designed to be connected to said sensor channels (20) for receiving respective measurement signals (i) therefrom, said channel branches (B0, . . . , B63; BR0, . . . , BR63) comprising respective current-to-frequency converters (210) and counters (220) for supplying count values (CT), representing a charge associated to a given channel (20), to a multiplexer (250; 550). According to the invention, said channel branches (BR0, . . . , BR63) supply their own outputs (CT0, . . . , CT63) directly to said multiplexer (550) and to an adder structure (240) comprising at least one first column (2401) of adders (2411) that adds up the values at the outputs (CT0, . . . , CT63) of the channel branches (Br0, . . . , BR63) to supply sum values (CT_100, . . . , CT_115, CT_200, . . . , CT_203, CT_300) at outputs thereof, said multiplexer (550) being configured for selecting, from the direct outputs (CT0, . . . , CT63) of the channel branches (BR0, . . . , BR63) and the outputs (CT_100, . . . , CT_115, CT_200, . . . , CT_203, CT_300) of the adder structure (240), a signal to be supplied to a readout electronics (400) for reading the channels (20), in particular in order to enable the channels necessary for detecting a given peak excursion via the multilayer-ionization-chamber sensor (10) without saturating.