Purpose: To assess the effect of time on the density, volume, and shape of two custom bolus materials
Methods: Two samples each of two custom bolus materials (PlatSil™ Gel-10 and SuperStuff bolus) were fabricated in 298 cc food storage containers following manufacturer recommended processes. One sample of each material remained in the container (labeled Control) while the other was removed from the container and stored as it would be for clinical use (labeled Clinical). Additionally, 8 oz of water was added to a fifth container. CT scans of the samples were acquired periodically over 30 days. All images were registered to the first CT image. The density, volume, and dice similarity coefficient (DSC) were calculated for each material for each image dataset. Between scans, the lids to the containers housing the Control samples were sealed to reduce air exposure. The SuperStuff clinical sample was wrapped tightly in plastic wrap and the PlaSil™ clinical sample remained unwrapped when in storage. All samples were stored on the same shelf in a cabinet between scans.
Results: The PlatSil™ Gel-10 samples (both Control and Clinical) and the SuperStuff Control sample maintained their volume (maximum difference of 2.7%), density (maximum change of 0.008 g/cc), and shape (minimum DSC of 0.972) throughout the study. For the Superstuff Clinical sample, the volume decreased by 32.9 %, the density increased from 1.039 to 1.063 g/cc, and the dice similarity coefficient decreased to 0.769 over the duration of the study.
Conclusion: The results of this study indicate that patient bolus fabricated using PlatSil™ Gel-10 will not change appreciably with respect to volume, density and shape throughout a course of radiation therapy. However, patient bolus fabricated with SuperStuff and stored wrapped in plastic wrap can have appreciable changes in volume, density and shape throughout a course of radiation therapy.