Use of 3D printing technology for custom bolus fabrication in the management of palmar or plantar fibromatosis with radiotherapy: A retrospective case series

Purpose: Palmar or plantar fibromatosis is a benign fibroproliferative disorder affecting the fascia of the hands or feet. Management involves surger y, typically reser ved for cases where progression limits function. Retrospective series demonstrate that radiation therapy (RT) can stabilize the disease course in many patients and improve symptoms in some cases. RT techniques vary between the use of electrons and superficial or orthovoltage photons and often require lead cutouts or custom boluses. We present a new approach demonstrating the implementation and effectiveness of three-dimensional (3D)-printed bolus material in patients receiving RT for fibromatosis. Materials and methods: A total of 3 patients, one with plantar and two with palmar fibromatosis, were treated with radiation using 3D- printed boluses over the past year. Bolus's design was based on computed tomography (CT) imaging data. Palmar patients were treated with a single en-face electron field, with a two-part accessory as a bolus and an immobilization device encasing the hand. The plantar case required 6MV photons delivered with a Volumetric Modulated Arc Therapy (VMAT) technique to cover the deeper target volume adequately. Dose and fractionation were based on guidelines from the Royal College of Radiologists in the United Kingdom. CT was used to assess printed shape and density accuracy. Results: The mean deviations in shape between the printed bolus pieces and their designs were all less than 0.4 mm. The differences in mean Hounsefield units (HU) between the printed boluses and their expected values were between 7 and 44 HU. No significant issues were encountered when applying the bolus to patients. The thermoluminescent dosimeters (TLD) used demonstrated dose accuracy to within TLD precision (5 %). Conclusions: 3D printing bolus technology represents a novel approach to treating fibromatosis with radiation. It offers superior dosimetry through the reduction of air gaps and by permitting custom bolus thickness. Also, it simplifies clinical set-up by acting as an immobilization device and a visual aid for daily field placement.