Consideration of Dose Error in Dynamic MLC IMRT Using MLC Speed Control with Dose Rate Change

Area of Science:

• Medical Physics
• Radiation Oncology
• Radiotherapy Technology

Background:

• Accurate dose delivery in dynamic multi-leaf collimator (MLC) intensity-modulated radiotherapy (IMRT) is crucial.
• MLC positional accuracy directly impacts delivered dose precision during dynamic IMRT.
• Real-time MLC speed control linked to dose rate variations is a key factor in dynamic IMRT accuracy.

Purpose of the Study:

• To investigate delivered dose errors in dynamic MLC IMRT by analyzing MLC speed control with dose rate changes.
• To evaluate the positional accuracy of the MLC during dynamic IMRT using trajectory log files.
• To assess the impact of MLC leaf speed on delivered dose accuracy and MLC gap errors.

Main Methods:

• Performed sweeping gap sequence irradiation with constant and varied MLC leaf speeds (0.6 to 5 cm/s).
• Evaluated MLC positional accuracy using trajectory log files.
• Conducted absorbed dose measurements with sweeping fields and analyzed delivered dose errors relative to MLC leaf speed changes.

Main Results:

• MLC positional errors and delivered dose changes were within 0.07 mm and 0.6%, respectively.
• No beam hold-off occurred under tested conditions.
• TrueBeam demonstrated real-time regulation of MLC leaf speed below 2.5 cm/s by adjusting dose rate, with MLC gap error estimated within 0.2 mm at maximum dose rate.

Conclusions:

• TrueBeam effectively regulates MLC leaf speed during dynamic MLC IMRT by adjusting dose rate in real-time.
• The system maintains high positional accuracy and dose delivery precision.
• Maximum dose rates can be utilized in dynamic MLC IMRT treatment planning, leading to reduced treatment times.