Room: Exhibit Hall
Purpose: To demonstrate that using modern treatment planning systems and fabrication technologies, one can inverse-plan the geometry of catheter trajectories within brachytherapy applicators to shape dose distributions to patient-specific targets and reduce dose to normal tissue.
Methods: Three points were investigated. First, an optimized plan was created with coverage of a lateral target around an inversely-planned vaginal cylinder while reducing dose to the contralateral side using linear channels. Second, to increase complexity, an abstract helical structure surrounding a vaginal cylinder was targeted. Using the TPS inverse optimization, two plans were created; one with linear channels and one with curvilinear channels. Third, another abstract structure was targeted using a plan with linear channels and a plan with sinusoidal-shaped channels. The geometry of the applicators was exported, and 3D printed with polylactic acid (PLA). The Hounsfield Units (HU) of the PLA as a function of cubic infill density was obtained from a CT scan of cylinders printed with varying infill percentages. Bolus was added to the applicators and radiochromic film was placed around the bolus. Each plan was delivered, and the measured dose distributions were compared.
Results: First, the V100% of the optimized applicator target for the first plan was 91.7%. By comparison, a single-channel cylinder treatment target V100% was 92.2%. The V100% of normal tissue for the optimized applicator and a typical cylinder treatment were 89.7cc and 134.3cc respectively. Second, the linear and curvilinear plans had conformity indices (CI) of 0.86 and 0.87, respectively. Third, the CI of the 5-7Gy volumes, using the linear channel plan as reference, was 0.87. Lastly, an infill percentage of 89% was found to match the HU of water.
Conclusion: This work shows the viability of designing and manufacturing patient-specific brachytherapy applicators for more conformal treatments. These methods will be further evaluated to determine clinical practicality.