A bore based medical system comprising a camera carrier configured to be mounted in the bore based medical system and configured to monitor and/or track patient motion within said bore based medical system during radiotherapy, the bore based medical system comprising: a rotatable ring-gantry mounted inside the bore based medical system and configured to emit a radiotherapy beam focused at an iso-center of the bore based medical system, wherein the ring-gantry is configured to rotate at least partly around a through-going bore having a front side and a back side, wherein said through-going bore is configured to receive from said front side, a movable couch configured to be moved into and out from the through-going bore, wherein further the through-going bore comprises an inner side facing an inside of the bore, and wherein the camera carrier having a ring-shaped body and configured to be mounted inside the bore in connection with the inner side of the through-going bore, and the camera carrier comprising: at least two treatment monitoring cameras mounted in connection with the inner side of through-going bore and together configured to cover a field of view including said iso-center focus point of the bore based medical system, wherein said two treatment monitoring cameras are configured record images of the patient lying on said movable couch during radiotherapy treatment so as to allow monitoring and/or tracking of any motion performed by said patient, characterised in that, the camera carrier comprises a first arch, which in a first end is configured to be connected to a left arch and in a second end is configured to be connected to a right arch, via substantially flexible joints (18a, 18b), wherein the left and right arches are further connected to each other through an adjustable expansion element, configured such that the left and right arches are adapted to be pushed apart and rotated with respect to the first arch, forming a circular shape of the ring-shaped camera carrier (1, 10) corresponding to the inner side of the bore. a rotatable ring-gantry mounted inside the bore based medical system and configured to emit a radiotherapy beam focused at an iso-center of the bore based medical system, wherein the ring-gantry is configured to rotate at least partly around a through-going bore having a front side and a back side, wherein said through-going bore is configured to receive from said front side, a movable couch configured to be moved into and out from the through-going bore, wherein further the through-going bore comprises an inner side facing an inside of the bore, and wherein the camera carrier having a ring-shaped body and configured to be mounted inside the bore in connection with the inner side of the through-going bore, and the camera carrier comprising: at least two treatment monitoring cameras mounted in connection with the inner side of through-going bore and together configured to cover a field of view including said iso-center focus point of the bore based medical system, wherein said two treatment monitoring cameras are configured record images of the patient lying on said movable couch during radiotherapy treatment so as to allow monitoring and/or tracking of any motion performed by said patient, characterised in that, the camera carrier comprises a first arch, which in a first end is configured to be connected to a left arch and in a second end is configured to be connected to a right arch, via substantially flexible joints (18a, 18b), wherein the left and right arches are further connected to each other through an adjustable expansion element, configured such that the left and right arches are adapted to be pushed apart and rotated with respect to the first arch, forming a circular shape of the ring-shaped camera carrier (1, 10) corresponding to the inner side of the bore.