Author: ChangSeon Kim, Andrew Lukban, Mario Serrano-Sosa, Ching-Ling Teng, Nadia M. Vassell 👨🔬
Affiliation: Northwell, Mount Sinai Beth Israel 🌍
Purpose:
The flexible nature of ballistic gelatin and 3D printed material such as PLA lend themselves to phantom studies in brachytherapy. While these materials can allow for easy simulation of catheters piercing tissue, the ability to physically measure depth is challenging. In this work, we devise a setup to compare percentage depth of ionization in water, PLA and ballistic gelatin with Ir-192 using a parallel-plate chamber.
Methods:
A CAD designed 3D printed fixture was created to hold 240 mm catheters in 3 media: water, PLA (the most common 3D printing filament), and ballistic gelatin (comprised of a 1:8 ratio of gelatin powder and water by weight). The data is compared to direct TG43 percentage depth dose calculations from the Oncentra treatment planning system. The data were normalized to 6 mm depth and represents the distance between the A10 parallel-plate chamber's nominal collection centroid and the center of the Ir-192 source surrounded by the catheter and at least 2.8 mm of test media.
Results:
Percentage depth of ionization of PLA and ballistic gelatin are within 1% of water for depths > 15 mm, which is at the approximate heel of the gradient. The measured curves are uniformly above the calculated TG43 PDD curve.
Conclusion:
This study sought to provide dosimetric validation of ballistic gelatin and PLA use as phantom creation media. Ballistic gelatin and PLA percentage depth of ionization for HDR Ir-192 are very similar to water and can be reasonably used as phantom material. However, differences between clinically delivered dose and what is calculated by the TG43 formalism is questioned since current measurement limitations include the parallel-plate chamber's geometry and non-homogeneous HDR source in media, as opposed to idealized sources in uniform media.