A gas target holder system comprising: - a body, which comprises: - a cavity configured to contain a target gas to irradiate with a particle beam emitted by a particle accelerator, the cavity comprising at least one portion of frusto-conical shape, a back closing a wide base of the portion of frusto-conical shape and an opening, opposite the back relative to the portion of frusto-conical shape, forming an entry in order for at least part of the particle beam to enter the cavity; - a cooling circuit comprising at least one duct which comprises an inlet and an outlet and surrounds at least part of the cavity; - a window, positioned facing the entry of the cavity to close the cavity, permeable to protons to enable introduction into the cavity of protons of the particle beam emitted by the particle accelerator, the window comprising a thin sheet permeable to at least part of the particle beam emitted by the particle accelerator and a support grid configured to withstand pressure differences between an inside of the cavity and an outside of the target holder system, the thin sheet being positioned between the support grid and the cavity; and - a support flange which holds the window and is hermetically secured on the body, and which comprises a mechanical fastening interface at an exit from a particle accelerator; the support flange being furthermore configured to hermetically close the cavity and to at least provide sealing between a vacuum formed in a beam line of the particle accelerator and a target gas under pressure contained in the cavity, the target holder system being characterized in that the support flange is furthermore configured to provide sealing between air outside the target holder system and a cooling fluid flowing in the cooling circuit. - a body, which comprises: - a cavity configured to contain a target gas to irradiate with a particle beam emitted by a particle accelerator, the cavity comprising at least one portion of frusto-conical shape, a back closing a wide base of the portion of frusto-conical shape and an opening, opposite the back relative to the portion of frusto-conical shape, forming an entry in order for at least part of the particle beam to enter the cavity; - a cavity configured to contain a target gas to irradiate with a particle beam emitted by a particle accelerator, the cavity comprising at least one portion of frusto-conical shape, a back closing a wide base of the portion of frusto-conical shape and an opening, opposite the back relative to the portion of frusto-conical shape, forming an entry in order for at least part of the particle beam to enter the cavity; - a cooling circuit comprising at least one duct which comprises an inlet and an outlet and surrounds at least part of the cavity; - a window, positioned facing the entry of the cavity to close the cavity, permeable to protons to enable introduction into the cavity of protons of the particle beam emitted by the particle accelerator, the window comprising a thin sheet permeable to at least part of the particle beam emitted by the particle accelerator and a support grid configured to withstand pressure differences between an inside of the cavity and an outside of the target holder system, the thin sheet being positioned between the support grid and the cavity; and - a support flange which holds the window and is hermetically secured on the body, and which comprises a mechanical fastening interface at an exit from a particle accelerator; the support flange being furthermore configured to hermetically close the cavity and to at least provide sealing between a vacuum formed in a beam line of the particle accelerator and a target gas under pressure contained in the cavity, the target holder system being characterized in that the support flange is furthermore configured to provide sealing between air outside the target holder system and a cooling fluid flowing in the cooling circuit.