Dosimetric evaluation of 3D printed bolus materials in breast cancer radiation therapy

Breast cancer is the most common malignancy among women and ranks second among all cancer types. In breast radiotherapy, high-energy photons such as 6 MV, 10 MV, or 15 MV are used depending on the technique applied. These photons deliver their maximum dose below the surface of the skin, which creates a "skin-sparing effect." Although beneficial in many cases, this characteristic may limit dose delivery to superficial lesions, necessitating the use of additional materials to enhance surface dose. Furthermore, due to the natural anatomical structure of the breast and previous surgical interventions, tissue irregularities or deficiencies may occur, complicating dose distribution during radiotherapy. In such cases, commercially available "bolus" materials tissue-equivalent substances are used to ensure accurate dose delivery. However, these commercial boluses are standardized in shape and size, and often fail to conform precisely to patient-specific anatomy. This can result in air gaps between the bolus and skin, leading to dose inaccuracies. Consequently, these issues may cause adverse skin reactions such as painful acute desquamation and chronic fibrosis. With the recent advancements in three-dimensional (3D) printing technologies, the ability to create patient-specific models has increased interest in their use in radiotherapy. In this study,a chest wall irradiation setup was created using a tissue-equivalent Alderson Rando phantom. The phantom was scanned using a CT simulator, and the images were saved in DICOM (.dcm) format. Using the Materialise Mimics software, segmentation of the DICOM images was performed. Subsequently, the region of interest was designed using Materialise 3-matic software, and the final model was converted to STL format for 3D printing. Two different boluses were fabricated using PLA (Polylactic Acid) and a medical-grade silicone material called G-series 5 Shore (G-5). These boluses were irradiated on a treatment unit, and dose measurements were taken using an optically stimulated luminescence (OSL) dosimeter. The results were then compared with those obtained using a conventional commercial bolus. The aim of this study is to compare and evaluate, from a dosimetric perspective, the responses of PLA and G-5 materials both produced with 3D printing technology with that of a routinely used commercial bolus material in radiotherapy