Quantification of planning target volume margin when using a robotic radiosurgery system to treat lung tumors with spine tracking

Standard margins of 5 mm on the ITV for patients with lung cancer being treated with stereotactic body radiation therapy are insufficient and may result in geographic misses of the tumor when spine tracking is used to locate the position of the tumor in the lung. Therefore, we recommend the addition of 5-mm margins in all directions for a total of 10 mm to take into account the change in position of the tumor relative to the spine from the time of simulation to treatment.