Improved delivery efficiency for step and shoot intensity modulated radiotherapy using a fast-tuning magnetron

Area of Science:

• Medical Physics
• Radiation Oncology
• Radiotherapy Technology

Background:

• Step-and-shoot intensity modulated radiotherapy (IMRT) delivery efficiency is crucial for patient treatment.
• Linear accelerators (LINACs) utilize magnetrons to generate microwave power for the electron beam.
• Older magnetron technology can limit the speed and efficiency of IMRT delivery.

Purpose of the Study:

• To evaluate the impact of installing fast-tuning magnetrons on IMRT delivery efficiency and beam start-up performance.
• To compare the performance of travelling wave linear accelerators before and after magnetron upgrades.
• To assess the dosimetric accuracy and beam characteristics post-installation.

Main Methods:

• Installation of fast-tuning magnetrons in three travelling wave linear accelerators.
• Comparison of IMRT delivery efficiency and beam start-up times pre- and post-installation.
• Analysis of dosimetric accuracy, beam symmetry, and flatness at various dose rates and energies.

Main Results:

• Average reduction in start-up and inter sub-field times by 3.0 seconds, with typical start-up now around 4 seconds.
• Average improvement in IMRT delivery efficiency of 30.7% (range 7.4-60.9%), varying with prescription complexity.
• Significant dosimetric accuracy improvement for low-dose sub-fields in the oldest accelerator; dose output within 2% for 1 MU and 1% for 2 MU sub-fields.

Conclusions:

• Fast-tuning magnetrons enhance the efficiency and speed of step-and-shoot IMRT delivery.
• The upgrade leads to faster treatment times and improved dosimetric accuracy, particularly for low-dose segments.
• Adoption of fast-tuning magnetrons is recommended for linear accelerators of this design performing step-and-shoot IMRT.