Exhibit Hall | Forum 7
Purpose: To study the dosimetric impact of the novel light-guided iWand P applicator (Liberty Vision, Portsmouth, NH) on depth-dose distribution of a high dose rate Y-90 disc source using Gafchromic EBT3 films and 3D-printed film holders
Methods: Gafchromic EBT3 film was cut into 3x4 cm2 pieces and calibrated (0-10 Gy) in water with the 6MV beam on a TrueBeam of our institute. Film holders for measurements were designed on TinkerCAD and fabricated using a low-cost desktop 3D printer (Ender 3 v2) with Polylactic Acid (PLA) filament and 0.4 mm nozzle. During measurements, film pieces were inserted into the holding space of the film holders, irradiated by a 6-mm Y-90 planar source with/without the applicator. Following AAPM TG-235 recommendations, irradiated films were processed and scanned using an Epson-10000XL flat-bed scanner. The 2D dose distribution and in-water central-axis depth-dose curves were then determined using the calibration files in RIT V6.8 Film package.
Results: Printing accuracy was measured within 0.5 mm. The central-axis depth-dose curves with/without the applicator were normalized to dose at 1 mm from the source surface. Depths were adjusted to the measurement with applicator for depth-dose curve as there is a gap between film edge and source surface. Both curves were fit to the exponential function, y=exp(a+bx+cx^2+dx^3+ex^4+fx^5) (R^2=0.999) and compared. Dose differences with/without the applicator at depths of 2 mm, 3mm, 4mm, and 5 mm were -0.30%, -0.83%, -0.04%, and -1.38%. Gamma analysis with 1mm/1% criteria was performed between the 2D dose distributions with RIT V6.8 and a passing rate of 96.7% was obtained.
Conclusion: The iWand P applicator demonstrated to have minimal impact on the depth-dose distribution of the Y-90 disc source. Reference data for treatment planning could be established from the more convenient source-only measurement or simulation.