SU-E-T-173: TomoTherapy Treatment Couch Velocity Verification Using TomoDose

Area of Science:

• Medical Physics
• Radiation Oncology

Background:

• Accurate TomoTherapy requires precise control of couch velocity and gantry rotation.
• The TG-148 protocol mandates quarterly film tests to ensure couch velocity constancy.
• Deviations in couch velocity can impact treatment accuracy and patient safety.

Purpose of the Study:

• To evaluate the feasibility of using the TomoDose quality assurance device to detect small variations in TomoTherapy couch velocity.
• To determine if TomoDose can identify deviations of 1-2% from the established baseline couch velocity.

Main Methods:

• The TomoDose unit's detector array was aligned with the TomoTherapy 'Y' jaws.
• A baseline table velocity of 0.5 mm/sec was established with a 1 cm collimator field size.
• Velocities were varied by 1% and 2% (0.490-0.510 mm/sec), with a constant translation time of 400 seconds.

Main Results:

• A 2% increase in couch velocity resulted in a field size increase to 20.39 cm; a 2% decrease resulted in 19.64 cm.
• A 1% increase in velocity yielded a field size of 20.18 cm; a 1% decrease yielded 19.76 cm.
• These results demonstrate a direct correlation between couch velocity and radiation field size.

Conclusions:

• Variations in couch velocity directly alter the radiation field size during TomoTherapy.
• The TomoDose device is capable of detecting small couch velocity variations as low as 1%.
• This method offers a feasible approach for quality assurance in TomoTherapy delivery.