Helical Tomotherapy
An Liu, Ph.D., Radiation
Oncology,
City of
Helical tomotherapy (HT) is a radiation therapy delivery device which represents an integration of technological advances in CT image-guided radiotherapy and IMRT, permitting the delivery of image-guided IMRT in a helical tomographic fashion. It utilizes a fan beam of radiation for treatment, which is inherently intensity modulated. The gantry rotates around the patient to treat from 51 angles. Helical tomotherapy employs a synchronously rotating gantry and a translating couch. The beam is shaped by a primary collimator of tungsten and a set of binary multileaf collimators (MLC). The primary collimator defines a geometrical projection that is 40cm wide in the transverse direction and 0.5-5 cm wide in the longitudinal direction at an isocenter located 85 cm from the source (85 cm SAD). The MLC further collimates the beam in the transverse direction. This MLC containes 64 interspersed tungsten leaves that is 6.25 mm wide in the transverse direction at the isocenter. The smallest beamlet at isocenter is 5 mm by 6.25 mm.
Clinical applications with Helical Tomotherapy are introduced. Cases includes intracranial radiosurgery, head & neck cancer, esophageal cancer, prostate cancer, retroperitoneal sarcoma, and total marrow irradiation. Finally, the advantage and disadvantage of helical tomotherapy verses other IGRT modalities will be summarized.