A Practical Distributed Virtual Bolus Strategy for Motion-Robust Superficial Dose Delivery in Breast Volumetric...

Area of Science:

• Medical Physics
• Radiation Oncology
• Radiotherapy Planning

Background:

• Superficial dose coverage in breast VMAT is challenged by interfractional motion and anatomical variations.
• Conventional skin flash strategies lack robustness against these changes.
• Improving motion robustness without dose escalation is critical for effective breast radiotherapy.

Purpose of the Study:

• To evaluate limitations of current skin flash strategies in breast VMAT.
• To propose and assess a practical distributed virtual bolus strategy for enhanced motion robustness.
• To improve superficial dose coverage and target robustness without dose escalation.

Main Methods:

• Six flash strategies were evaluated in twelve left-sided breast VMAT plans.
• A triple virtual planning bolus (tBar) strategy distributed discrete bolus segments along the breast contour.
• Robustness was assessed using deformation-based motion simulations (up to 15 mm) and evaluated using skin shells and dose-volume metrics.

Main Results:

• The tBar strategy maintained stable superficial coverage across all simulated motion scenarios.
• PCTV2 V95% was preserved above 97% for displacements up to 15 mm with the tBar strategy.
• The tBar strategy reduced high-dose penalty by up to 56.59% compared to virtual target expansion.

Conclusions:

• A distributed virtual bolus strategy provides motion-robust superficial dose delivery in breast VMAT.
• This approach effectively limits high-dose escalation.
• The tBar strategy offers a practical, physics-informed solution for improving motion tolerance in arc-based breast radiotherapy.