Room: Davidson Ballroom A
Purpose: To evaluate the capability of time-resolved dosimetry using mirror-less scintillation detector (TRMLSD) for dynamic megavoltage radiation fields.
Methods: TRMLSD consist of a scintillator plate (PI-200) and a small sized camera (HERO5). The size and weight is 40.5 Ã— 32.5 Ã— 15.5 cm3 and 1.72 kg. The effective field size is 17.6 Ã— 17.6 cm2 with 0.086 mm of spatial resolution. Scintillation was recorded with 0.042 sec of time resolution. Without a reflection mirror, the image captured has geometry distortion. To correct the geometry, a perspective and a lens correction algorithm was applied. To convert the brightness to the dose, the dependence of brightness on the distance between the camera and each point on the scintillator was tested and corrected. Frame-based noise reduction technique has been developed to remove hot-pixels while maintaining image resolution. To evaluate important characteristics of the dosimeter, the reproducibility, linearity, dose profile with wedge filter, and gamma analysis with EBT3 film was performed with 6MV linear accelerator (Novalis Tx).
Results: Reproducibility was assessed by five consecutive measurements at 20 and 200 cGy. The measurements were within the 3% error, respectively. The Linearity was evaluated from 0 to 260 cGy. The r-square value of the fitting curve was 0.9998 and the RMSE value was 1.010. For all test plans (wedge filter, homogeneous and heterogeneous phantoms), the passing rate of gamma test were 98.53, 98.46 and 97.37 % with 3%/3mm criterion.
Conclusion: We demonstrated the feasibility of using TRMLSD in two-dimensional dosimetry of dynamic treatments therapy such as VMAT, IMRT, and IMPT. The excellent precision, accuracy of device indicate that TRMLSD has potential as a high-accuracy quality assurance tool for patient plan verification.
Funding Support, Disclosures, and Conflict of Interest: This research was supported by the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT & Future Planning (2013M2A2A7043507).