Author: Slade J. Klawikowski, Natalya V. Morrow, Haidy G. Nasief, Eric S. Paulson, An Tai, Hualiang Zhong 👨🔬
Affiliation: Department of Radiation Oncology, Medical College of Wisconsin 🌍
Purpose: Gafchromic film is commonly used for quality assurance in SRS/SBRT. However, its application in low-dose measurements, such as monitoring doses on cardiac implantable electronic devices—where slight dose variations may influence clinical decisions—remains underexplored. In this study, we detail the development and commissioning of an in-house film program for in-vivo dosimetry.
Methods: Gafchromic EBT-3 films were cut into small pieces to form 20×20 mm² dosimeters. These dosimeters were sandwiched between solid-water slabs, irradiated with 6-MV photon beams and stored in the dark at room temperature for 24 hours. The exposed films were scanned using an Epson scanner (EX1200000XL) in reflective mode at 75 dpi, producing 16-bit, three-channel TIFF files. A piecewise-defined rational function was adopted for each channel to characterize film responses in the low (1–50 cGy) and high (50–300 cGy) dose ranges. The parameters of this function were optimized using a least-squares method. The derived response curves were validated using 20 measured datasets. The green and blue channels were insensitive in the low- and high-dose ranges, respectively, and were consequently excluded from the integration of channel responses in these ranges.
Results: The channel-integrated response derived from piecewise calibration functions achieved dosimetric accuracies of 4.2% ± 4.3% and 3.2% ± 2.7% in the low- and high-dose ranges, respectively. When using the red channel alone, accuracies were within 10.7% ± 10.6% and 4.1% ± 3.1% in the two ranges. When using global rational calibration functions, the average errors were 36.5% for the red channel and over 80.1% for the green and blue channels, indicating that piecewise functions are required for calibration.
Conclusion: This study confirms the feasibility of using small pieces of Gafchromic film for dose measurements in both low- and high-dose ranges. The developed program could be useful for in-vivo dosimetry and other clinical applications.