KEY POINTS
- The study evaluated a room-temperature-malleable bolus with a density of approximately 1.59 g/cm³. Phantom measurements used a 1 cm bolus with 6 MV flattening-filter-free beams, while clinical outcomes were reviewed in 55 patients treated for superficial skin tumours.
- Measured depth doses were compared with Eclipse AAA and Acuros XB calculations. Acuros XB showed closer agreement, with a mean deviation of −0.1%, standard deviation of 0.5%, and maximum deviation of 1.5%, compared with a mean deviation of 1.7% and maximum of 3.4% with AAA.
- A 1 cm bolus was sufficient to overcome the build-up region of the 6 MV flattening-filter-free beam. CT-derived Hounsfield units were used directly, without manually assigning bolus density or material.
- Air-gap effects depended strongly on field size. For a 3 × 3 cm² field, skin-dose loss was 5.9% with a 1 cm gap, 12.7% with 1.5 cm, and 21.4% with 2 cm.
- With a 10 × 10 cm² field, corresponding dose losses were smaller at 1.4%, 2.4%, and 3.9%. Dynamic sweeping-gap deliveries behaved similarly to the large static field, suggesting that integral irradiated area mattered more than the individual MLC aperture width.
- The clinical cohort had a median age of 81 years and received a median dose of 50 Gy, commonly using 48 Gy in 16 fractions or 63 Gy in 21 fractions. Median follow-up was only 5.7 months.
- Acute dermatitis was grade 1 in 49.1%, grade 2 in 47.3%, and grade 3 in 3.6%; no grade 4 events or toxicity-related treatment interruptions occurred. Three patients (5.4%) developed local failure during the short follow-up period.
CLINICAL TAKEAWAY
A conformable high-density bolus modeled with Acuros XB is a practical option for superficial treatment using modern megavoltage photon platforms. Close skin contact remains critical, particularly for targets smaller than approximately 5 cm, where centimetre-scale air gaps can produce substantial underdosage.