Total scalp irradiation: A study comparing multiple types of bolus and VMAT optimization techniques

Area of Science:

• Radiation Oncology
• Medical Physics
• Biomedical Engineering

Background:

• Total scalp irradiation presents challenges in achieving accurate dose delivery due to complex head contours.
• Effective bolus design and radiation therapy planning are crucial for optimizing treatment outcomes.

Purpose of the Study:

• To evaluate different silicone bolus designs for their adherence, placement time, and impact on air gaps in total scalp irradiation.
• To investigate Volumetric Modulated Arc Therapy (VMAT) optimization settings for achieving adequate target coverage while minimizing normal tissue toxicity.

Main Methods:

• Three silicone bolus designs (flat, hat, custom) were assessed on anthropomorphic head phantoms for fit and air gap quantification.
• Bolus placement times were recorded, and dosimetric effects of air gaps were evaluated in treatment planning.
• A noncoplanar VMAT technique was explored using generalized Equivalent Uniform Dose (gEUD) penalties to optimize brain dose reduction.

Main Results:

• Custom and generic hat boluses demonstrated significantly shorter application times compared to flat boluses.
• Custom boluses resulted in significantly smaller air gap volumes compared to flat boluses.
• No significant dosimetric differences in planning target volume (PTV) coverage were observed despite variations in air gaps. A gEUD alpha of 2 minimized mean brain dose.

Conclusions:

• Custom-designed silicone boluses offer improved efficiency and accuracy for total scalp irradiation compared to traditional flat boluses.
• A straightforward VMAT template with specific optimization settings (gEUD alpha=2) can facilitate the creation of high-quality treatment plans for total scalp irradiation.