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Custom Bolus Fabrication Process Improvement with Thermoplastic and CNC Machined Molds

M Lafreniere*, A Villa, E Hirata, M Sharma, K Hasse, E Lam, M Descovich, University of California San Francisco, San Francisco, CA


(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

Room: AAPM ePoster Library


Bolus types currently used clinically include materials such as Superflab, wax (paraffin or Bee’s wax), thermoplastics, wet towels, or discarding boluses entirely and treating the patient’s surface with an electron boost. When using Superflab boluses, air gaps can form between the patient and the bolus, leading to planned and delivered dose distributions discrepancies. The major downside of custom manual wax bolus fabrication is the significant amount of labor time required, which can also lead to chronic injuries (tendinitis). Thermoplastic sheets can be bought pre-made from a manufacturer, but this is prohibitively expensive (3 boluses produced weekly amount to ~$17000 yearly). I propose using computer assisted design (CAD) software to produce custom made CNC machined aluminum molds, to fabricate in-house thermoplastic bolus sheets.


Using a freely available CAD software (FreeCAD), aluminum molds can be designed to obtain a bolus with clinically relevant dimensions with a thickness precision down to 0.1 mm (FreeCAD design files made available on demand). Thermoplastic pellets are melted in water at 140F, and put into the bottom part of the mold, with the top part compressing the bolus down to the desired thickness.


Compared to a previous manual wax bolus fabrication process, this thermoplastic bolus fabrication process can save radiation oncology departments about 5 hours of work for each bolus made, and in addition cut down yearly product costs from ~$2200 to ~$720 (thermoplastic being more affordable). There are no significant dosimetric differences between the wax bolus and the thermoplastic bolus. Using molds would decrease the bolus thickness uncertainty associated with the manual bolus fabrication process.


With the time, effort and cost savings potential, we recommend the transition to thermoplastic bolus.


Breast, Dose Uniformity


TH- External Beam- Photons: General (most aspects)

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