Results of a two-year quality control program for a helical tomotherapy unit

Area of Science:

• Medical Physics
• Radiation Oncology

Background:

• Helical tomotherapy (HT) is an advanced intensity modulated radiation therapy (IMRT) technique using helical irradiation.
• HT integrates a rotating gantry, moving couch, and multileaf collimator (MLC) with integrated megavoltage CT (MVCT) for image guidance.

Purpose of the Study:

• To report the findings of a two-year quality control (QC) program for a helical tomotherapy unit.
• To assess the physical and dosimetric stability and reliability of the HT unit.

Main Methods:

• Adapted conventional linear accelerator (Linac) acceptance and QC protocols for HT.
• Evaluated mechanical-geometrical alignment, static and dynamic beam characteristics, gantry-couch-MLC synchronization, and MVCT image quality.
• Utilized ionization chambers, films, and phantoms for measurements.

Main Results:

• Average output variation was within +/-1% for static and rotational conditions, with 98% of data within action levels.
• Daily absolute dose verification showed dose reproducibility within +/-1.2% and +/-2.2% in low and high dose gradient regions.
• Mechanical alignment and positioning accuracy were within +/-1mm, and synchrony tests showed stability within +/-2mm.

Conclusions:

• The quality control program demonstrated good reproducibility for all mechanical and dosimetric performance aspects of the helical tomotherapy unit.
• The findings support the reliability and stability of HT for clinical radiation treatments.