Limitations with Other Radiotherapy Approaches:
Breathing motion of tumor
Lung cancers actually move along a sometimes variable and unpredictable path during the respiratory cycle, sometimes moving several centimeters or more (9). To compensate for this breathing motion using conventional radiotherapy, a larger volume of normal tissue around the cancer needs to be treated with full dose radiation, which limits the total dose of radiation that may be safely given.

Yellow shaded area = radiotherapy margin expansion to accomodate breathing