Custom-made, 3D-printed bolus cap for a case of scalp metastasis: A single-institution study

Treating multiple scalp metastasis in patients is challenging due to the large area that needs to be treated and the complex structure of the scalp. Dose coverage with coplanar fields is hard to optimize with the Halcyon machine's three degrees of freedom (3DoF) couch movement. A potential solution is to use a 3D-printed bolus, which can be designed to fit the scalp contour. This covers more area to improve dose delivery, ensuring that the skin receives the necessary radiation dose while protecting organs at risk (OaR's). A total dose of 39 Gy was delivered to a 71-year-old patient in 13 fractions as a total scalp irradiation (TSI) treatment. The Volumetric Modulated Arc Therapy (VMAT) technique employed four full arcs, which covered the planning target volume (PTV) and ensured optimal dose distribution across the treatment area. A 3D-printed bolus was created using a flexible resin for patient comfort and improved positioning as well as dose delivery. 95% of the PTV received 98.85% of the prescribed dose, with a maximum dose of 107.1% and a conformity index (CI) of 0.95. At the six-month follow-up, the patient showed no signs of scalp metastases, confirming the success of the treatment across the entire scalp. The use of the custom-made, 3D-printed bolus contributed significantly to the treatment success. This study marks the first clinical experience with 3D-printed boluses in our country. Our previous validation study demonstrates that a designed 3D-printed bolus, when integrated into the clinical setup, can provide solution for customizing treatment in cases involving superficial tumors that require good dose distribution.