Low-Cost iPhone-Assisted Processing to Obtain Radiotherapy Bolus Using Optical Surface Reconstruction and 3D-Printing.

Patient specific boluses can increase the skin dose distribution better for treating tumors located just beneath the skin with high-energy radiation than a flat bolus. We introduce a low-cost, 3D-printed, patient-specific bolus made of commonly available materials and easily produced using the "structure from motion" and a simple desktop 3D printing technique. Nine pictures were acquired with an iPhone camera around a head phantom. The 3D surface of the phantom was generated using these pictures and the "structure from motion" algorithm, with a scale factor calculated by a sphere fitting algorithm. A bolus for the requested position and shape based on the above generated surface was 3D-printed using ABS material. Two intensity modulated radiation therapy plans were designed to simulate clinical treatment for a tumor located under the skin surface with a flat bolus and a printed bolus, respectively. The planned parameters of dose volume histogram, conformity index (CI) and homogeneity index (HI) were compared. The printed bolus plan gave a dose coverage to the tumor with a CI of 0.817 compared to the CI of 0.697 for the plan with flat bolus. The HIs of the plan with printed bolus and flat bolus were 0.910 and 0.887, respectively.