Author: Michael Dingfelder, Homeira Faridnejad 👨🔬
Affiliation: East Carolina University, Department of Physics, East Carolina University 🌍
Purpose: To use Gafchromic film for measurement of the dose delivered by low-energy (2-4 MeV) protons to living cells.
Methods: Five different types of Gafchromic films were tested for dosimetry under irradiation with 2-4 MeV protons at the East Carolina University accelerator laboratory. We obtained calibration curves for correlation between dose and gray value in two different ways: (i) using a calibrated 320 kV X-ray source giving doses from cGy to kGy and (ii) irradiating films under vacuum with 2, 2.5, 3, and 4 MeV protons. 24 hours after irradiation, the samples were scanned with a high-resolution scanner, and the resulting images were analyzed with ImageJ to obtain the gray values in the red channel. Subsequently, we irradiated HDV-2 films in air at different energies, currents, times, and distances from the exit window to evaluate the beam profile, dose rates, and uncertainties.
Results: Of the five films tested, the Gafchromic HDV-2 film is best suited for low-energy protons since the active layer is directly exposed to radiation. Results from films that were irradiated by protons did not agree with X-ray irradiated films due to the different modes of dose deposition Films irradiated with different proton energies yielded similar calibration curves. Experiments with different thicknesses of air between exit windows and cells demonstrated a widening of the beam and a decrease in dose rate.
Conclusion: Gafchromic HDV-2 films are suited for determining the dose administered by low-energy protons. Calibration curves for low-energy proton measurement are best obtained by irradiating with known doses from protons of similar energy.