Evaluation of High-Resolution Radiochromic Film Dosimetry for Peak and Valley Characterization In Microbeam Radiation Therapy
Abstract
Purpose
To evaluate the accuracy of high-resolution radiochromic film dosimetry for characterizing peak and valley dose distributions in microbeam radiation therapy (MRT). This study aims to establish film as a benchmark for validating the spatial and dosimetric accuracy of alternative dosimetry systems in high-gradient fields.
Methods
Gafchromic EBT-4 films were utilized with a high spatial resolution scan of 4 microns. To ensure precise registration, films were marked with fiducials and underwent pre-irradiation scanning using a flatbed scanner. Films were irradiated using a 50 kVp focused x-ray source (FXRS) with a 50-micron nominal focal spot size; each film received 5 stripes of radiation that were about .09mm wide. Post-irradiation scans were performed more than 24 hours after exposure to allow for stable polymerization. Red channel dosimetry was employed to minimize artifacts, and film-to-calculation registration was performed to evaluate dose profiles.
Results
In the absence of a reference dosimeter, four irradiation groups were identified. The measured mean peak doses and their respective standard deviations were: 2.28 ± 0.16 Gy, 3.27 ± 0.14 Gy, 3.67 ± 0.18 Gy, and 4.09 ± 0.17 Gy. Spatial characterization yielded a Full Width at Half Maximum (FWHM) of 0.090 mm with a standard deviation of 0.002 mm, compared to the nominal beam width of 0.05 mm. The Peak-to-Valley Dose Ratio (PVDR) average standard deviation between individual stripes was 1.60 for peak doses below 4 Gy and 36.47 for doses above 4 Gy.
Conclusion
Radiochromic film dosimetry provides the high spatial resolution necessary to accurately capture the steep dose gradients encountered in MRT. These gradients are most effectively evaluated through the PVDR of individual films, which our results demonstrate is highly consistent for doses below 4 Gy. Furthermore, the discrepancy between measured beam width and nominal focal spot size highlights the film's sensitivity in identifying experimental alignment issues.