David Dean

Highly accurate rendering of the external and internal geometry of bone tissue engineering scaffolds affects fit at the defect site, loading of internal pore spaces with cells, bioreactor-delivered nutrient and growth factor circulation, and scaffold resorption. It may be necessary to render resorbable polymer scaffolds with 50 µm or better accuracy to achieve these goals. This level of accuracy is available using Continuous Digital Light Processing (cDLP) which utilizes a DLP® (Texas Instruments, Dallas, TX) chip. One such additive manufacturing device is the envisionTEC (Ferndale, MI) Perfactory®. To use cDLP we integrate a photo-crosslinkable polymer, a photo-initiator, and a biocompatible dye. The dye attenuates light, thereby limiting the depth of polymerization. In this study we fabricated scaffolds using the well-studied resorbable polymer, poly(propylene fumarate) (PPF), titanium dioxide (TiO₂) as a dye, Irgacure® 819 (BASF [Ciba], Florham Park, NJ) as an initiator, and diethyl fumarate as a solvent to control viscosity.

This study proposes and simulates an inverse treatment planning and a continuous dose delivery approach for the Leksell Gamma ^® (LGK, Elekta, Stockholm, Sweden) which we refer to as “Tomosurgery.” Tomosurgery uses an isocenter that moves within the irradiation field to continuously deliver the prescribed radiation dose in a raster‐scanning format, slice by slice, within an intracranial lesion. Our Tomosurgery automated (inverse) treatment planning algorithm utilizes a two‐stage optimization strategy. The first stage reduces the current three‐dimensional (3D) treatment planning problem to a series of more easily solved 2D treatment planning subproblems. In the second stage, those 2D treatment plans are assembled to obtain a final 3D treatment plan for the entire lesion. We created Tomosurgery treatment plans for 11 patients who had already received manually‐generated LGK treatment plans to treat brain tumors. For the seven cases without critical structures (CS), the Tomosurgery treatment plans showed borderline to significant improvement in within‐tumor dose standard deviation (STD) (, or excluding case 2) and conformality , respectively. In three of the four cases that presented CS, the Tomosurgery treatment plans showed no statistically significant improvements in dose conformality , and borderline significance in improving within‐tumor dose homogeneity ; CS damage measured by or (i.e., irradiated CS volume that receives or of the maximum dose) showed no significant improvement in the Tomosurgery treatment plans ( and , respectively). However, the overall CS dose volume histograms were improved in the Tomosurgery treatment plans. In addition, the LGK Tomosurgery inverse treatment planning required less time than standard of care, forward (manual) LGK treatment planning (i.e., vs ) for all 11 cases. We expect that LGK Tomosurgery will speed treatment planning and improve treatment quality, especially for large and/or geometrically complex lesions. However, using only collimators could greatly increase treatment plan delivery time for a large brain lesion. This issue is subject to further investigation.