Management of respiratory motion in radiotherapy
Respiratory motion has a significant effect on the dose delivery to targets in the chest and upper abdominal cavities. To compensate for these effects relatively large margins are added to a clinical target volume (CTV), thus limiting the maximum dose delivery to these patients. Respiratory motion management may reduce the margin around a moving CTV, but is also appropriate when the procedure will increase normal tissue sparing. To account for organ motion 4D imaging technology was developed, which allows viewing of volumetric CT images changing over the fourth dimension: time. The next step is creating a 4D plan from a 4D CT set in which the tumour motion is taken into account using one of the strategies that is available to compensate for respiratory motion. The technologies mostly applied are motion-encompassing methods, respiratory gated techniques, breath-hold techniques, forced shallow-breathing methods, and respiration-synchronized techniques.
Firstly, tumour motion should be measured for each patient for whom respiratory motion is a concern. Then a choice has to be made between one of the interventional strategies taking into account the tolerance of the patient to a specific approach and the resources available in the department. Respiratory motion management generally involves advanced equipment, education and training in the use of complex technology, and the implementation of a dedicated QA programme.
Introduction to References
An introduction to and overview of 4D treatment planning and 4D IMRT delivery are provided in the textbook on Image-Guided IMRT by Bortfeld et al. Management of respiratory motion in RT has been discussed in detail in the AAPM Report and in J. Van Dyk's Compendium, and briefly in the IAEA Handbook.