No abstract

Pre-treatment patient-specific quality assurance (QA) is critical to prevent radiation accidents. The electronic portal imaging device (EPID) is a dose measurement tool with good resolution and a low volume-averaging effect. EPIbeam—an EPID-based portal dosimetry software—has been newly installed in three institutions in Korea. This study evaluated the efficacy of the EPID-based patient-specific QA tool versus the PTW729 detector (a previously used QA tool) based on gamma criteria and planning target volume (PTV). A significant difference was confirmed through the R statistical analysis software. The average gamma passing rates of PTW729 and EPIbeam were 98.73% and 99.60% on 3 mm/3% (local), 96.66% and 97.91% on 2 mm/2% (local), and 88.41% and 74.87% on 1 mm/1% (local), respectively. The p-values between them were 0.015 (3 mm/3%, local), 0.084 (2 mm/2%, local), and less than 0.01 (1 mm/1%, local). Further, the average gamma passing rates of PTW 729 and EPIbeam according to PTV size were 99.55% and 99.91% (PTV < 150 cm3) and 97.91% and 99.28% (PTV > 150 cm3), respectively. The p-values between them were 0.087 (PTV < 150 cm3) and 0.036 (PTV > 150 cm3). These results confirm that EPIbeam can be an effective patient-specific QA tool.

To implement dual-energy cone-beam computed tomography (CBCT), a 1 to 3 mm thick copper filter was applied in front of the kilovolt generator mounted on a medical linear accelerator. The energy calibration was performed from three energy peaks among the electromagnetic radiation, gamma rays, emitted by the 192 Ir source. The energy spectrum was measured using a cadmium zinc telluride (CZT) detector. A figure-of-merit (FOM) value was defined and evaluated in order to consider both the increase in the mean energy and the decrease in the intensity according to the filter. For a 1 mm thick filter, the FOM values were 0.82 and 0.92 for tube voltages of 100 and 120 kVp, respectively. The intensity was maintained reasonably and the effect of increasing the mean energy was evident, thus indicating its suitability for implementing dual-energy CBCT.