Dosimetric evaluation of unlaminated radiochromic films exposed to an Americium-241 source using measurements and Monte Carlo simulations

Radiochromic GafChromic film models are widely used in clinical settings for quality assurance during cancer treatment planning. Although these films are extensively studied in photon dosimetry, research on their application in α-particle dosimetry remains limited. With the growing use of α-particles in cancer therapy, it is important to establish film dosimetry protocols tailored to α-particles. Unlike photons, α-particles are charged, have a high linear energy transfer, and induce significantly greater biological damage, highlighting the need for specialized dosimetric approaches.

This study aimed to evaluate the response of various unlaminated GafChromic film models including EBT3, EBT-XD, and HD-V2, irradiated with an ²⁴¹Am α-particle source, with combined experimental film irradiation and Monte Carlo (MC) simulations.

In this study, unlaminated EBT3, EBT-XD, and HD-V2 film pieces were irradiated with an ²⁴¹Am disk source at various exposure times within a dark box. A detailed comparison was performed across the three film models, focusing on uncertainties and relative dose errors. Film analysis was conducted using a custom Python script, extracting normalized pixel values from the green channel. Additionally, a MC-based user code was developed using the Geant4 simulation toolkit to model the ²⁴¹Am source and calculate the dose rates in the active layers of the films and in water. The mean dose rates were also calculated in a 1 mm diameter region of interest. These simulated dose rates were employed to convert film exposure times into absorbed doses for both the active layers and water, establishing a reference dosimetry protocol for α-particles across the three radiochromic GafChromic film models.

The mean dose rates within a 1 mm diameter circular region of interest in the active layers of the three unlaminated GafChromic film models were determined to be 3.77 ± 0.002 Gy/min for EBT3, 4.04 ± 0.0022 Gy/min for EBT-XD, and 4.25 ± 0.0017 Gy/min for HD-V2. When the film material was changed to water, the dose rate was increased 14.3% for EBT3, 19.2% for EBT-XD, and 15.0% for HD-V2, with EBT3 showing the closest match to water-equivalence. Calibration curves for each film model were generated by fitting a power function to their responses. Refinements to the dose range were necessary to achieve an uncertainty below the 5% threshold. Among the models, HD-V2 required the most adjustments to its dose range and exhibited the highest levels of experimental, fit, and total uncertainties, along with the largest relative dose errors.

This study investigated α-particle dosimetry protocols for unlaminated EBT3, EBT-XD, and HD-V2 GafChromic film models using experimental irradiations and MC simulations. Although EBT3 and EBT-XD demonstrate strong potential for α-particle quality assurance in treatment planning, the HD-V2 film model requires further investigation before it can be recommended for this application.