A Study Utilizing 3D Printing in Patients Undergoing External Beam Radiation Therapy

In radiation therapy, high-energy radiation beams treat tumors by damaging cancer cells. Treatment plans are designed with the goal of limiting exposure to adjacent healthy tissues. Commonly used radiation beams demonstrate the "skin-sparing effect" which means that the radiation dose builds up after the beam enters the skin and thus the maximum dose is reached at some depth beneath the skin. For many tumors, this spares the skin from unnecessary exposure while ensuring cancer cells beneath the skin receive the maximum dose. For cancers that lie at or just below the skin surface, however, it is desirable for the maximum dose be present at the skin surface. In such cases, a bolus (material with properties similar to tissue) is used to mimic tissue and is placed above the skin. Dose build up occurs within the bolus, thus allowing the maximum dose to be reached at the skin surface. Aside from the treatment of superficial tumors, boluses have recently been used for modulated electron radiation therapy (MERT). For MERT, the bolus thickness is varied so that the dose at a specific depth can be varied at different locations within the tissue. With this technique, the bolus is customized for a patient's specific anatomy and thus radiation exposure to healthy tissue is minimized.

Boluses are typically made from moldable materials such as paraffin wax or superflab. Conventional bolus preparation has its disadvantages; the patient is required to be present, it can be time intensive and it is dependent on the skill of the fabricator. Furthermore, the degree of conformity to the patient's skin is limited and, as a result, there can be significant air gaps between the bolus and the patient's skin. Such air gaps have been shown to create significant reduction in the surface dose.

The goal of the present study is to improve the current process of bolus preparation by creating customized boluses with 3D printing. Customized boluses can be designed in Varian eclipse software and then imported into 3D modeling software such as 3D Slicer. The 3D model can then be converted into STL (Stereolithography) format which can be interpreted by the 3D printer software. Several preliminary studies have reported success in creating such boluses. One study reported good fit without air gaps (Kim) in their 3D printed bolus. Additionally, several studies modeled tissue dose distributions for 3D printed boluses and found results were similar to those obtained for conventional boluses.

For the current study, the Investigators will enroll participants who require boluses as part of their treatment plan. Both a conventional and 3D bolus will be fabricated for each participant. Computer simulation of dose distributions will be used to compare dosimetric parameters. Additionally, air gaps for both boluses will be measured. For each participant, the bolus that results in a more optimized dose distribution will be used for the participant's actual treatment. Conducting the study will necessitate each enrolled participant to undergo an additional CT scan to simulate treatment with the 3D printed bolus.