Dynamic region-of-interest cone-beam CT for image-guided postmastectomy radiotherapy

Postmastectomy radiation therapy (PMRT) is often prescribed for patients with advanced breast cancer and has been shown to reduce local-regional recurrence and improve survival. The radiotherapy target is the chest wall, axillary lymph nodes, and the supraclavicular fossa. Patients are normally positioned for therapy with arms extended above the head in order to minimize both dose to the uninvolved arm tissue, and perturbations to the delivered dose distribution. The shoulder is the most mobile joint in the human body and difficult to position with a high level of reproducibility, thus the target area can be substantially affected by shoulder and arm position. Accordingly, this treatment is a good candidate for the regular use of imaging for patient position verification. Many linear accelerators today are equipped with kilovoltage X-ray imaging systems capable of cone-beam CT imaging, and CBCT is potentially an excellent tool for image-guided radiotherapy (IGRT) of the breast and chest wall.