# Development of Patient Specific Conformal 3D-Printed Devices for Dose Verification in Radiotherapy
###### Abstract  
In radiation therapy, a bolus is used to improve dose distribution in superficial tumors; however, commercial boluses lack conformity to patient surface leading to the formation of an air gap between the bolus and patient surface and suboptimal tumor control. The aim of this study was to explore 3D-printing technology for the development of patient-specific conformal 3D-printed devices, which can be used for the radiation treatment of superficial head and neck cancer (HNC). Two 3D boluses (0.5 and 1.0 cm thick) for surface dose build-up and patient-specific 3D phantom were printed based on reconstruction of computed tomography (CT) images of a patient with HNC. The 3D-printed patient-specific phantom indicated good tissue equivalency (HU = \(-\)32) and geometric accuracy (DSC = 0.957). Both boluses indicated high conformity to the irregular skin surface with minimal air gaps (0.4-2.1 mm for 0.5 cm bolus and 0.6-2.2 mm for 1.0 cm bolus). The performed dose assessment showed that boluses of both thicknesses have comparable effectiveness, increasing the dose that covers 99% of the target volume by 52% and 26% for single field and intensity modulated fields, respectively, when compared with no bolus case. The performed investigation showed the potential of 3D printing in development of cost effective, patient specific and patient friendly conformal devices for dose verification in radiotherapy.  
phantom; bolus; 3D printing; radiotherapy +
Footnote †: journal:the conformity of the bolus to the patient's head and neck surface area. Alternatively, commercially available flat boluses (e.g., SuperFlab) consisting of flexible sheets of uniform thickness could be used. The main disadvantage of commercial boluses is the lack of conformity to irregular surface such as the nose, ear and scalp. Placement of such bolus on the patient's head and neck surface results in the formation of air gaps between the bolus and patient surface, which in turn contribute to surface dose reduction and inhomogeneous dose distributions [11; 12; 13]; therefore, the challenges mentioned above should be taken into account when producing patient-friendly personalized boluses.  
Three-dimensional printing technologies enable the fabrication of various shapes from a digital model. 3D printing is currently being employed for a variety of medical applications such as patient-specific implant and external prostheses, surgical guides as well as a research and educational training tool [14; 15]. Additionally, in the field of radiation oncology, 3D-printing potential is remarkable. Research published during the last few years have explored the implementation of 3D-printing technologies for the production of different patient-specific devices for radiotherapy such as compensators, immobilization devices, dosimetric phantoms and boluses [16; 17; 18; 19; 20; 21; 22]; however, successful application of these devices in the clinical setting necessitate more extensive evaluation procedures including their validation on real patients.  
The aim of this study was to evaluate the feasibility of applying a low cost, recyclable, home-made 3D bolus of uniform thickness along with a personalized 3D phantom, both produced from reconstructed CT data of a real patient using 3D-printing technologies, in radiotherapy clinical settings. While taking into account that conformity issue is one of the most important factors contributing to accurate dose distribution in the target, the research we performed was focused on investigating the conformity between 3D bolus and 3D patient-specific phantom replicating the face of a real patient with nasopharynx cancer. The requirement for the accurate reproducibility of the 3D-printed shapes were also considered in this paper.