Room: AAPM ePoster Library
This study is to develop an in-house dosimetric verification system include a simple solid-phantom and independent dose-calculation program for quality assurance (QA) of high-dose rate brachytherapy (HDR-BT).
Dosimetric verification for single dwell-position was implemented to evaluate the feasibility of our system. All measurements were performed using Gafchromic EBT3 film at manufactured acrylonitrile butadiene styrene (ABS, density: 1.09 g/cm³) phantom. The measured dose distribution was used to the verification by comparing with calculated dose distribution. However, dose distribution calculated by commercialized treatment planning system (TPS) is inaccurate to utilize the verification because it is based on TG-43 formalism which utilized the water-based dosimetric parameters. Thus, we developed an independent dose-calculation program for the verification in the ABS phantom. Although the program is basically similar to the TPS in that it adopts the TG-43 formalism, it can calculate doses more accurately in the ABS phantom by applying conversion factors (CF(r)) for radial-distance (r) between water and ABS. The CF(r) was obtained by using Monte-Carlo simulation (GATE4, version 8.0).
The CF(r) was 0.89 at 0.5 cm. It was gradually increased with increasing of r and converged to 1.07 at 5.0 cm. Point doses below 1 cm of the source were 400, 373.4, and 372.9 cGy as per TPS, our program, and the measurement, respectively. Gamma passing rate with 3%/3 mm criteria was 92.64% (TPS) and 97.98% (our program) for comparing of film-measured and calculated dose distributions, respectively.
We developed the dosimetric verification system for HDR-BT by using simple ABS phantom and the independent dose-calculation program. With the single dwell-position test, we confirmed that it is possible to perform the dosimetric verification more conveniently.
Funding Support, Disclosures, and Conflict of Interest: This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea Government (Ministry of Science, ICT & Future Planning) (No. 2018R1D1A1B07049159 and No. 2018R1A2B2005343) Disclosures and Conflict of Interest: The authors have no conflicts of interest.
Brachytherapy, Quality Assurance, Dosimetry