The pace of change in radiation oncology continues to accelerate, paralleling the advances in computer technology and diagnostic imaging. Multimodality imaging with CT scans, MRIs, and PET scanning is not only used for diagnosis and staging, but also fused with radiographic studies for radiation therapy planning. Intensity modulated radiation has become routine in the treatment of prostate, head and neck, and many pelvic malignancies. The ability of this latest planning and treatment delivery technique allows radiotherapy with true precision. Planning margins can be just a few millimeters from gross tumor, thus sparing normal tissue and allowing for dose escalation.
This can be problematic, however, when your target moves. Any intrathoracic malignancy, as well as upper abdominal malignancies such as gastroesophageal, pancreatic, biliary, and hepatic tumors, can move along with the diaphragmatic motion of breathing. Respiratory movement can displace a primary lung tumor by 4 cm between peak exhalation and inhalation. This has been long recognized and requires increasing the margins of treatment around the tumor to prevent a geometric miss of treatment delivery during the extremes of respiratory excursion. This expansion often includes normal critical structures, such as lung. So much for precision planning!