A method comprising: determining, by a processing device, a full motion range of a target pathological anatomy of a patient over a heartbeat cycle or a respiration cycle of the patient, wherein the full motion range of the target pathological anatomy comprises positions of the target pathological anatomy in three dimensions over the heartbeat cycle or the respiration cycle, and wherein the full motion range defines a three-dimensional internal target volume ITV; identifying, by the processing device, a partial motion range of the target pathological anatomy, wherein the partial motion range is a subset of the full motion range of the target pathological anatomy that comprises positions of the target pathological anatomy in an untrackable plane that is normal to an imaging axis or positions of the target pathological anatomy in an untrackable axis that is normal to an imaging plane; generating, by the processing device, a one-dimensional partial-ITV or a two-dimensional partial-ITV based on the identified partial motion range, wherein the one-dimensional partial-ITV is a space swept by the target pathological anatomy as the target pathological anatomy moves through the partial motion range in the untrackable axis, the one-dimensional partial-ITV being generated by projecting the three-dimensional ITV onto the untrackable axis, and wherein the two-dimensional partial-ITV is a space swept by the target pathological anatomy as the target pathological anatomy moves through the partial motion range in the untrackable plane, the two-dimensional partial-ITV being generated by projecting the three-dimensional ITV onto the untrackable plane; and generating a treatment plan that causes a system to: determine when the target pathological anatomy is located at positions that are within the partial-ITV; activate a radiation treatment beam while the target pathological anatomy is located at the positions within the partial-ITV, to treat the space swept by the target pathological anatomy as the target pathological anatomy moves through the partial motion range; and deactivate the treatment beam while the target pathological anatomy is outside of the partial-ITV. determining, by a processing device, a full motion range of a target pathological anatomy of a patient over a heartbeat cycle or a respiration cycle of the patient, wherein the full motion range of the target pathological anatomy comprises positions of the target pathological anatomy in three dimensions over the heartbeat cycle or the respiration cycle, and wherein the full motion range defines a three-dimensional internal target volume ITV; identifying, by the processing device, a partial motion range of the target pathological anatomy, wherein the partial motion range is a subset of the full motion range of the target pathological anatomy that comprises positions of the target pathological anatomy in an untrackable plane that is normal to an imaging axis or positions of the target pathological anatomy in an untrackable axis that is normal to an imaging plane; generating, by the processing device, a one-dimensional partial-ITV or a two-dimensional partial-ITV based on the identified partial motion range, wherein the one-dimensional partial-ITV is a space swept by the target pathological anatomy as the target pathological anatomy moves through the partial motion range in the untrackable axis, the one-dimensional partial-ITV being generated by projecting the three-dimensional ITV onto the untrackable axis, and wherein the two-dimensional partial-ITV is a space swept by the target pathological anatomy as the target pathological anatomy moves through the partial motion range in the untrackable plane, the two-dimensional partial-ITV being generated by projecting the three-dimensional ITV onto the untrackable plane; and generating a treatment plan that causes a system to: determine when the target pathological anatomy is located at positions that are within the partial-ITV; activate a radiation treatment beam while the target pathological anatomy is located at the positions within the partial-ITV, to treat the space swept by the target pathological anatomy as the target pathological anatomy moves through the partial motion range; and deactivate the treatment beam while the target pathological anatomy is outside of the partial-ITV. determine when the target pathological anatomy is located at positions that are within the partial-ITV; activate a radiation treatment beam while the target pathological anatomy is located at the positions within the partial-ITV, to treat the space swept by the target pathological anatomy as the target pathological anatomy moves through the partial motion range; and deactivate the treatment beam while the target pathological anatomy is outside of the partial-ITV.