Purpose: Eyeshields offer protection to the organs underneath by virtue of the beam energy attenuation through the materials. This is especially important for radiotherapy of the eyelid with a need to protect the cornea and lens. An important specification from the manufacturer is the transmission. As a quality assurance (QA) measure and part of acceptance, this needs to be confirmed onsite. We describe our clinical filmless approach for a quick evaluation of the eyeshield prior to use on patients.
Methods: Our work was based on the Tungsten eyeshield (RPD Inc., Albertville, TN) which comes in 2 thicknesses, 2mm/3mm and 5 sizes. We used the 3mm, S-size with a 0.5 and 1mm Al caps. In the first method, we used an IC profiler to determine the transmission with and without the Al caps. The RPD transmission is specified at a depth of 3mm. The IC profiler has an inherent depth of 9mm; therefore, we used several additional water slabs to measure transmission at several depths and by linear extrapolation determined the transmission at 3mm. In the second method, we used Exradin1DH 97241 diode, inherent effective depth of 0.8mm, with additional slab on the diode to measure transmission at 3mm depth.
Results: The RPD specified transmission at 3mm, 9MeV beam was 3.3%, 2.9%, and 2.8% for the eyeshield with no cap, 0.5mm Al cap and 1mm Al cap respectively. The corresponding IC profiler values (inherent depth of 9mm) were 10.9%, 11.3%, and 11.9%. However, after applying the linear extrapolation to 3mm depth, the corresponding transmission were 1.0%, 1.3%, and 2.1%. The corresponding measured transmission using Exradin1DH were 3.2%, 3.1%, and 3.3%.
Conclusion: We have described a simple technique of acceptance and QA of an eyeshield prior to patient use. This was done for a 9MeV energy but can be repeated for 6MeV.
Electron Therapy, Quality Assurance