An apparatus for charged hadron therapy verification by detecting and/or quantifying prompt gammas produced when irradiating a target with a charged hadron beam, the beam being directed along a beam line, said apparatus comprising: • a collimator formed of a first material and provided with a single slit-shaped portion which comprises a material of a lower thickness and/or density than said first material, said slit-shaped portion being configured to be arranged perpendicularly to the beam line and facing the target, • a detection means (3,4) suitable for detecting said prompt gammas and • a calculation and representation means, characterized in that: • the thickness of the collimator and the shape of the slit-shaped portion as seen in cross-section taken perpendicularly to the longitudinal axis of the slit-shaped portion are configured to allow the passage of prompt gammas emitted at least from a zone of the target corresponding to a portion of the beam line within said target, said portion of the beam line being larger than the width of the slit-shaped portion, so that the slit-shaped portion allows to detect prompt gamma emitted not only from the direction which is at 90° with respect to the beam direction, • said detection means (3,4) is configured to detect prompt gammas passing through the slit-shaped portion, said prompt gammas being emitted from a plurality of portions within said zone of the target, • said calculation and representation means is configured to derive from a detected prompt gamma a value representative of the dose at the location from where said prompt gamma is emitted, and to represent a dose-related distribution for said plurality of portions of the zone, thereby allowing to estimate the beam range within said target, • said detection means (3,4) and said calculation and representation means are configured to calculate and represent said value in each of said plurality of portions of said zone arranged along the beam line, to thereby obtain a one-dimensional view of the dose-related distribution within said zone, • said detection means comprises a scintillator arranged at a distance from said slit-shaped portion, and having a flat surface parallel to the beam line and facing said slit-shaped portion, and at least one array of photon counting devices associated with said scintillator. • a collimator formed of a first material and provided with a single slit-shaped portion which comprises a material of a lower thickness and/or density than said first material, said slit-shaped portion being configured to be arranged perpendicularly to the beam line and facing the target, • a detection means (3,4) suitable for detecting said prompt gammas and • a calculation and representation means, • the thickness of the collimator and the shape of the slit-shaped portion as seen in cross-section taken perpendicularly to the longitudinal axis of the slit-shaped portion are configured to allow the passage of prompt gammas emitted at least from a zone of the target corresponding to a portion of the beam line within said target, said portion of the beam line being larger than the width of the slit-shaped portion, so that the slit-shaped portion allows to detect prompt gamma emitted not only from the direction which is at 90° with respect to the beam direction, • said detection means (3,4) is configured to detect prompt gammas passing through the slit-shaped portion, said prompt gammas being emitted from a plurality of portions within said zone of the target, • said calculation and representation means is configured to derive from a detected prompt gamma a value representative of the dose at the location from where said prompt gamma is emitted, and to represent a dose-related distribution for said plurality of portions of the zone, thereby allowing to estimate the beam range within said target, • said detection means (3,4) and said calculation and representation means are configured to calculate and represent said value in each of said plurality of portions of said zone arranged along the beam line, to thereby obtain a one-dimensional view of the dose-related distribution within said zone, • said detection means comprises a scintillator arranged at a distance from said slit-shaped portion, and having a flat surface parallel to the beam line and facing said slit-shaped portion, and at least one array of photon counting devices associated with said scintillator.