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

Purpose To investigate bolus design and VMAT optimization settings for total scalp irradiation. Methods Three silicone bolus designs (flat, hat, and custom) from .decimal were evaluated for adherence to five anthropomorphic head phantoms. Flat bolus was cut from a silicone sheet. Generic hat bolus resembles an elongated swim cap while custom bolus is manufactured by injecting silicone into a 3D printed mold. Bolus placement time was recorded. Air gaps between bolus and scalp were quantified on CT images. The dosimetric effect of air gaps on target coverage was evaluated in a treatment planning study where the scalp was planned to 60 Gy in 30 fractions. A noncoplanar VMAT technique based on gEUD penalties was investigated that explored the full range of gEUD alpha values to determine which settings achieve sufficient target coverage while minimizing brain dose. ANOVA and the t‐test were used to evaluate statistically significant differences (threshold = 0.05). Results The flat bolus took 32 ± 5.9 min to construct and place, which was significantly longer (p