SU‐F‐I‐73: Surface Dose from KV Diagnostic Beams From An On‐Board Imager On a Linac Machine Using Different Imaging Techniques and Filters

Abstract

Purpose:To quantitatively investigate the surface dose deposited in patients imaged with a kV on‐board‐imager mounted on a radiotherapy machine using different clinical imaging techniques and filters.Methods:A high sensitivity photon diode is used to measure the surface dose on central‐axis and at an off‐axis‐point which is mounted on the top of a phantom setup. The dose is measured for different imaging techniques that include: AP‐Pelvis, AP‐Head, AP‐Abdomen, AP‐Thorax, and Extremity. The dose measurements from these imaging techniques are combined with various filtering techniques that include: no‐filter (open‐field), half‐fan bowtie (HF), full‐fan bowtie (FF) and Cu‐plate filters. The relative surface dose for different imaging and filtering techniques is evaluated quantiatively by the ratio of the dose relative to the Cu‐plate filter.Results:The lowest surface dose is deposited with the Cu‐plate filter. The highest surface dose deposited results from open fields without filter and it is nearly a factor of 8–30 larger than the corresponding imaging technique with the Cu‐plate filter. The AP‐Abdomen technique delivers the largest surface dose that is nearly 2.7 times larger than the AP‐Head technique. The smallest surface dose is obtained from the Extremity imaging technique. Imaging with bowtie filters decreases the surface dose by nearly 33% in comparison with the open field. The surface doses deposited with the HF or FF‐bowtie filters are within few percentages. Image‐quality of the radiographic images obtained from the different filtering techniques is similar because the Cu‐plate eliminates low‐energy photons. The HF‐ and FF‐bowtie filters generate intensity‐gradients in the radiographs which affects image‐quality in the different imaging technique.Conclusion:Surface dose from kV‐imaging decreases significantly with the Cu‐plate and bowtie‐filters compared to imaging without filters using open‐field beams. The use of Cu‐plate filter does not affect image‐quality and may be used as the default in the different imaging techniques.