Assessing the Reliability of 3D-Printed Custom Silicone Boluses in Radiotherapy: Thickness and Air Bubble Considerations

This study aimed to evaluate the impact of air bubbles, thickness variations, and density differences occurring during the fabrication of 3D-printed silicone boluses on radiation dose distribution, thereby providing evidence for clinical quality assurance. Custom silicone boluses were fabricated using 3D-printed molds with varying vacuum degassing times (1, 5, and 10 minutes). Air bubble size and depth were quantified using scanner image analysis, while density and Hounsfield unit (HU) values were compared with a commercial bolus. Dosimetric evaluation was performed using a VitalBeam linear accelerator (6 MV photons) and a MatriXX 2D detector, comparing treatment planning system (TPS) calculated doses with measured doses across a 3×3 grid. Surface dose distributions were further analyzed using EBT3 film. Results showed that bubble size increased with longer vacuum times, interpreted as coalescence due to limited degassing and silicone viscosity. The density of 3D boluses ranged from 0.980–1.104 g/cm³ (commercial: 0.988 g/cm³), with HU values of +240 to +250 (commercial: −110). In point-wise comparisons, mean dose differences were less than 1% for 1- and 5-minute samples, and approximately 1% for 10 minutes, with all conditions within |Δ| ≤ 3%. Film analysis confirmed equivalent surface dose distributions. These findings suggest that 3D-printed silicone boluses are clinically feasible without complex degassing procedures.