Re-Imagining Radiotherapy Bolus As a Soft Robot: A Preliminary Investigation
Poster
aapm2026_poster_44x44_bolus_bot.pdf Hosted by AAPM · 0.8 MBAbstract
Purpose
Robotic bolus has potential to enhance surface dosimetry by reducing air gaps through adaptive surface contouring and providing immobilization for treatment regions. This study evaluated filler materials for a jamming-style robotic bolus as an initial proof-of-concept. Jamming was selected as a mechanism because it enables passive shape conformity and stiffness without complex actuation. The work supports development of a patient-agnostic, reusable, homogeneous, non-adhesive, robotic bolus using simple pneumatic control.
Methods
Prototype devices were fabricated with hydrated silicone (SmoothOn EcoFlex-30), degassed and cured in 3D printed molds, consisting of an inner 6cm x 6cm grid region with optional outer petals. The grid region was designed to maintain uniform thickness over a treatment region under deflection and take advantage of granular jamming for stabilization and shape conformity to the surface. Jamming materials and mixtures of round glass microbeads (100-170 mesh), coarse sugar, and ground coffee were evaluated for radiological homogeneity using a 6MV beam normalized to an open field. EPID measurements were normalized to an open field and analyzed within central ROIs.
Results
A soft robotic prototyping method was established using curable silicone. EPID measurements demonstrated that none of the fillers matched silicone in 6MV transmission, although glass beads showed a small improvement (1.3%) over air. A mixture of 60/40 weight percent sugar and glass beads had the lowest max/min and avg/min intensity ratios in the ROI (1.017 and 1.009, respectively). Evacuation enabled temporary, non-adhesive fixation, suggesting potential for reproducibility and patient comfort.
Conclusion
A fabrication process and candidate filler materials were established for jammed soft robotic bolus designs, using radiological homogeneity as a design constraint. Mixed sugar-glass bead fillers demonstrated improved uniformity relative to air. Temporary, non-adhesive fixation could be achieved via mild suction, with further research supporting appropriate design of hybrid systems.