Use of reduced dose rate when treating moving tumors using dynamic IMRT

Area of Science:

• Medical Physics
• Radiation Oncology

Background:

• The interplay effect, a phenomenon in dynamic radiation therapy, can cause significant discrepancies between planned and delivered radiation doses.
• Accurate dose delivery is crucial for effective cancer treatment and minimizing side effects.

Purpose of the Study:

• To investigate the influence of dose rate on the interplay effect in intensity-modulated radiation therapy (IMRT).
• To determine if reducing dose rate can mitigate dose discrepancies caused by target motion during treatment.

Main Methods:

• Fifteen dynamic IMRT and five hybrid IMRT plans were created for five patients.
• The impact of motion on delivered dose was experimentally evaluated at dose rates of 200 and 400 MU/min.
• Various target amplitudes and periods were tested to simulate different motion scenarios.

Main Results:

• Maximum dose discrepancies for dynamic IMRT fields were 18.5% at 400 MU/min and 10.3% at 200 MU/min.
• Reducing the dose rate to 200 MU/min increased the percentage of fields where dose discrepancies remained within 5% or 10%.
• For target amplitudes up to 2 cm, a dose rate of 200 MU/min effectively limited daily dose discrepancies to within 10%.

Conclusions:

• Lowering the dose rate in IMRT is an effective strategy to reduce dose discrepancies arising from the interplay effect.
• A dose rate of 200 MU/min demonstrates improved accuracy in maintaining target coverage during motion, particularly for smaller amplitudes.