Delivery time reduction for mixed photon-electron radiotherapy by using photon MLC collimated electron arcs

Area of Science:

• Radiation Oncology
• Medical Physics
• Radiotherapy Technology

Background:

• Mixed-beam radiotherapy (MBRT) combines photon and electron beams for improved treatment planning.
• Intensity-modulated electron arcs with dynamic gantry rotation (Arc-MBRT) may reduce delivery time compared to static electron beams.
• A robust treatment planning process (TPP) is needed to implement Arc-MBRT clinically.

Purpose of the Study:

• To develop and investigate a TPP for photon multileaf collimator (pMLC)-based Arc-MBRT.
• To compare the dosimetric and delivery time characteristics of Arc-MBRT plans with static MBRT (Static-MBRT) and photon-only plans.
• To validate the dosimetric accuracy of Arc-MBRT plans.

Main Methods:

• Extended an existing TPP for Static-MBRT to incorporate dynamic electron arcs and intensity modulation.
• Utilized a sliding window technique for intensity modulation and optimized electron arc parameters.
• Performed simultaneous photon and electron intensity modulation optimization followed by Monte Carlo dose calculation.
• Created and compared Arc-MBRT, Static-MBRT, and photon-only plans for four breast cancer cases.
• Validated two Arc-MBRT plans using film dosimetry.

Main Results:

• Arc-MBRT plans achieved dosimetric similarity to Static-MBRT plans and outperformed photon-only plans.
• Mean heart dose was reduced by 32% in MBRT plans compared to photon-only plans.
• Arc-MBRT plans had delivery times comparable to photon-only plans, significantly faster than Static-MBRT.
• Film measurements confirmed dosimetric accuracy with a gamma passing rate >98% (3% global, 2 mm).

Conclusions:

• A TPP for pMLC-based Arc-MBRT was successfully developed.
• Arc-MBRT demonstrates potential for improved plan quality and reduced heart dose, similar to Static-MBRT.
• Arc-MBRT maintains short delivery times, facilitating clinical adoption of advanced MBRT techniques.