A radiation system includes a support, a capsule rotatably coupled to the support, a radiation source movably coupled to the capsule, wherein the radiation source is configured to provide a treatment radiation beam, and is capable of being turned on or off in response to a control signal, and a collimator located next to the radiation source, wherein the capsule defines a space for accommodating a portion of a patient, and includes a shielding material for attenuating radiation resulted from an operation of the radiation source, and wherein the shielding material is configured to limit a radiation exposure level to 5 mR/hr or less within 3 meters from an isocenter.