Design, Validation and Implementation of a Novel 3D-Printed Chest Wall Bolus
Abstract
Purpose
To develop a novel composite mesh bolus (CMB) as an alternative to hand-molded bolus in chest wall radiotherapy. The CMB is a 3D-printed flexible mesh with silicone layers. Its design allows surface conformity, skin adhesion, a reproducible bolus effect and compatibility with surface gated optical tracking systems (SGRT).
Methods
The CMB consists of a 3D-printed chainmail made of a biocompatible resin with silicone-filled compartments. To assess water-equivalent thickness of the CMB, EBT4 film dosimetry (Ashland, USA) was performed using VMAT and direct fields delivered on a solid-water phantom. To test the CMB under clinical conditions, the body contour of four chest wall patients was extracted and 3D-printed to fit on top of a Lungman phantom (Kyoto Kagaku, Japan) with inserts for film dosimetry. Each phantom was scanned with CMB and SuperStuff successively to evaluate surface conformity. Clinical treatment plans were transferred onto the scanned phantoms and delivered on a linear accelerator. Films placed in the inserts were used to measure dose under each bolus for the clinical plans. CMB visibility on CRAD and VisionRT was assessed for a range of skin tones.
Results
Film measurements in solid water showed that the CMB is comparable to a 4 mm water-equivalent bolus. Plan film measurements under CMB and SuperStuff agreed within 2% and were within 5% of the calculated dose. On the phantom CT scans, the CMB fit was visually comparable to the SuperStuff. The CMB was visible on CRAD and VisionRT for all tested conditions.
Conclusion
The CMB provides an adequate skin bolus effect under clinical beam arrangements and presents good conformity to skin surface. It requires no prior preparation, is biocompatible, and can be washed and reused, making it a cost- and resource-efficient alternative. Since its implementation, it has been used clinically for over 70 fractions.