Megavoltage computed tomography: an emerging tool for image-guided radiotherapy

Area of Science:

• Medical Physics
• Radiotherapy Technology
• Medical Imaging

Background:

• Helical tomotherapy integrates linear accelerator and CT scanner features for image-guided intensity-modulated radiation therapy (IMRT).
• Megavoltage CT (MVCT) generated by this system enables daily setup verification through image guidance.
• This study evaluates the image quality, radiation dose, and clinical utility of MVCT from a helical tomotherapy prototype.

Purpose of the Study:

• To assess the image quality of MVCT.
• To determine the absorbed radiation doses associated with MVCT.
• To evaluate the clinical practicality of MVCT for patient setup verification.

Main Methods:

• Phantom studies were conducted to evaluate MVCT capabilities.
• MVCT images from human patients were analyzed.
• MVCT scans were compared with conventional kilovoltage CT (kVCT) scans.

Main Results:

• MVCT detected contrast differences as small as 3% in phantoms, with good resolution for small objects (1.2-1.6 mm).
• Human subject MVCT imaging provided sufficient detail for patient repositioning and showed minimal artifact with metallic objects compared to kVCT.
• Patient scans were rapid (1-5 minutes) with absorbed doses of 1.5-3 cGy.

Conclusions:

• MVCT is a valuable tool for pretreatment patient positioning and setup verification.
• High-resolution, 3D MVCT images from helical tomotherapy are suitable for daily setup verification.
• MVCT shows potential for imaging near metal prostheses and in adaptive radiotherapy, with ongoing research to enhance image quality and reduce dose.