Micrometer-resolved film dosimetry using a microscope in microbeam radiation therapy

Area of Science:

• Medical Physics
• Radiation Oncology
• Dosimetry

Background:

• Microbeam radiation therapy (MRT) is an experimental tumor treatment using narrow, parallel radiation beams.
• Accurate dose measurement is critical for MRT's clinical translation but presents significant challenges.
• Radiochromic film dosimetry offers a potential solution for validating MRT dose distributions.

Purpose of the Study:

• To investigate the feasibility of using radiochromic film dosimetry with microscopic readout for validating peak and valley doses in MRT.
• To assess the accuracy and reproducibility of this dosimetry method for future clinical MRT applications.

Main Methods:

• Gafchromic HD-810 and HD-V2 films were exposed to MRT fields at the European Synchrotron Radiation Facility (ESRF).
• Films were scanned using a microscope, and results were compared with Monte Carlo calculations.
• Image analysis tools and protocols were developed for accurate dosimetry, with analysis of resolution, noise, and energy dependence.

Main Results:

• Dosimetry achieved 5% accuracy in peak doses and 10-15% in valley doses, with 5 × 1000 µm² resolution.
• Key uncertainties included statistical noise, film inhomogeneity, and calibration errors, particularly at low doses (<50-70 Gy).
• HD-V2 films exhibited higher noise but better low-energy performance than HD-810 films, which had lower noise but higher energy dependence.

Conclusions:

• Both Gafchromic film types are suitable for MRT dosimetry, with microscopic readout surpassing previous microdensitometry methods.
• Careful image analysis is essential, and low-photon-energy dosimetry requires caution due to film energy sensitivity.
• HD-V2 films offer advantages in low-energy scenarios, while HD-810 films provide lower noise for high-resolution needs.