Assembly for radiation therapy, for example proton therapy, comprising: a carrier for supporting a patient, an immobilisation mask connectable with the carrier for immobilizing a body part of the patient onto the carrier and connection means for connecting the carrier with the immobilisation mask, wherein the immobilisation mask is manufactured from thermoplastic material, wherein the connection means contain at least one profile that on a first side contains first connection means along which the profile is connectable to the carrier and on a second side opposite the first, contains second connection means along which the profile is connectable to the immobilisation mask, wherein the first connection means are provided, in the connected state, to engage corresponding connection means along the outer edge of the carrier characterized in that the first connection means comprise a first lower lip that is provided, in the connected state, to extend along the carrier, further characterized in that the first connection means comprise a second and third lower lip (6, 7) at opposite sides of the first lower lip, wherein the second and third lower lip (6, 7) are provided to extend along a lower side of the carrier, further characterized in that the first connection means comprise an upper lip that is provided, in the connected state, to extend along an upper surface of the carrier, and the first lower lip is provided, in the connected state, to extend along the lower side of the carrier, wherein the edge of the carrier is held between said first lower lip and said upper lip and further characterized in that the first lower lip is arranged resiliently. a carrier for supporting a patient, an immobilisation mask connectable with the carrier for immobilizing a body part of the patient onto the carrier and connection means for connecting the carrier with the immobilisation mask, wherein the immobilisation mask is manufactured from thermoplastic material, wherein the connection means contain at least one profile that on a first side contains first connection means along which the profile is connectable to the carrier and on a second side opposite the first, contains second connection means along which the profile is connectable to the immobilisation mask, wherein the first connection means are provided, in the connected state, to engage corresponding connection means along the outer edge of the carrier characterized in that the first connection means comprise a first lower lip that is provided, in the connected state, to extend along the carrier, further characterized in that the first connection means comprise a second and third lower lip (6, 7) at opposite sides of the first lower lip, wherein the second and third lower lip (6, 7) are provided to extend along a lower side of the carrier, further characterized in that the first connection means comprise an upper lip that is provided, in the connected state, to extend along an upper surface of the carrier, and the first lower lip is provided, in the connected state, to extend along the lower side of the carrier, wherein the edge of the carrier is held between said first lower lip and said upper lip and further characterized in that the first lower lip is arranged resiliently.