SU-E-T-203: Sensitivity Study on the Use of Computed Radiography for Linac Routine Quality Assurance - Light/radiation Field Coincidence

Abstract

Purpose: To investigate the accuracy of using computed radiography(CR) system for the light/radiation field coincidence test and to verify that the accuracy level can be achieved by using this technique as a linac routine quality assurance check. Methods: Kodak 2000RT CR system together with a Kodak Flexible Phosphor plate was used in this study. The phosphor plate was exposed with background radiation (cover the entire plate), radiation field and then field light. All measurements were carried out by using 6 MV X‐rays (Varian 21iX) and 100 cm SSD setup. The room lights were off during the entire measure procedure to control the amount of light field discharge on the CR plate. Results: Delivering 1 and 2 MUs to background and radiation fields, respectively and shining the field light for 35 seconds can provide a good quality of contrast to notify discrepancy (darker or lighter stripe along field edges) between light and radiation fields. Users can visually indicate the discrepancy approximately 1 mm without using any tool. For discrepancy less than 1 mm in the penumbra region between light and radiation fields, by analyzing the light/radiation field edge profiles of CR plate response, accuracy of less than 1 mm can be achieved. Conclusions: The CR system can be used as a replacement of the film to perform the linac routine QA procedures. For light/radiation coincidence test, the result can be directly determined by eyes if using TG‐40 tolerance (i.e., < 2mm). Compared to conventional marking film technique, our method does not involve any intervention between light/radiation fields, which makes it possible to reach higher accuracy level (<1 mm).