Room: Exhibit Hall | Forum 7
Purpose: Gafchromic film provides useful dose verification for high dose rate (HDR) Iridium-192 brachytherapy. A calibration curve is created using EBT3 film in water and in 3D printed ABS plastic to confirm that 3D-printed ABS plastic blocks can be used interchangeably with water for routine film calibration for I-192 sources.
Methods: EBT3 film pieces were irradiated in water with an HDR Ir-192 source at dose levels ranging from 0-800 cGy to obtain a calibration curve. A custom template was used to secure the film in a reproducible position in water between two HDR catheters, each 5 cm away. A 3D-printed ABS block was used to generate an independent calibration curve. The 2 cm ABS block with 1 cm of solid water positioned the catheter 3 cm away from the film. Film was handled according to AAPM TG-55 recommendations. Film was read 24 hours post-irradiation on an Epson Expression 11000XL flatbed scanner. A positioning template was used to achieve reproducible scanning location and confirm orientation while scanning. The mean pixel value for the irradiated regions of interest was used to obtain the optical density (OD), and the net optical density (NOD) in the calibration curve.
Results: The measured data fits well with the polynomial equations, all having an RÂ² value less than 1% deviation. Calibration curves in 3D-printed ABS plastic blocks were overall within 1.4% of the calibration curves for water for the dose range tested in the red channel. Sources of measurement uncertainties included scan-to-scan variability, sensitivity with time of scan post-irradiation, film position reproducibility in water, and size of region of interest selected during film analysis. Combined uncertainties were evaluated in 1.8%.
Conclusion: The results of this study confirmed that film calibration obtained in 3D-printed ABS blocks is an accurate method to verifying HDR brachytherapy doses.