Evaluation of three radiochromic film types in x-ray minibeam radiation therapy pre-clinical dosimetry

Background

Minibeam radiation therapy (MBRT) is an unconventional experimental technique that uses a strong spatial modulation of the dose. The narrow beam widths employed (0.5 to 1.0 mm) require the use of high-spatial resolution detectors. One of the most frequently employed is radiochromic films.

Purpose

This work aims at providing a systemic and thorough assessment of the performance of different radiochromic films and their calibration procedure for X-ray MBRT.

Methods

Three commonly used radiochromic films having different dynamic range and composition (GAFchromic EBT3 and EBT-XD (Ashland, Bridgewater, New Jersey, USA), and OrthoChromic OC-1 (OrthoChrome Inc, Hillsborough, New Jersey, USA) were evaluated. Different calibration procedures commonly employed in the literature were followed up. Then, the three different film types were irradiated with X-ray MBRT, and the impact of the different film types and calibration procedures were assessed by measuring peak and valley doses.

Results

Significant dosimetric differences, especially in the peak-to-valley dose ratio determination, may result from the use of different film types calibrated following different procedures. Additionally, the OC-1 films deemed not to be able provide the required spatial resolution to resolve beam of less than 1 mm FWHM.

Conclusions

The unconventional nature of MBRT requires unconventional dosimetry methods and procedures, which must be carefully evaluated. The combination of film type and calibration procedure employed is critical in minibeam radiation therapy, may lead to large uncertainties and should be attentively chosen.