SU‐E‐T‐80: Development of IMRT Postal Audit Phantom Using Radiophotoluminescence Glass Dosimeter

Purpose: The purpose of this study is to develop IMRT postal audit phantom using radiophotoluminescence glass dosimeter, and to report initial experiences of the phantom. Method and Materials:We developed the IMRT postal audit phantom. The phantom can be inserted with both RPL glass dosimeter, GD‐302M (Asahi Techno Glass) for point dose verification and Radiochromic film, EBT2 (ISP) for relative planar dose verification. In the dedicated phantom, RPL glass dosimeter can be placed in 4 positions corresponding to target and 1 position to OAR. The EBT2 film can be inserted on the central transverse plane in the phantom. The phantom was made of water substitute material, Tough Water WE‐211 (Kyoto kagaku). for the initial experiences, 7 fields segmental MLCIMRT was planned with XiO (Elekta) using 6 & 10 MV from Clinac iX‐S. In addition, to evaluate the measurement accuracy of RPL glass dosimeter, point doses with ionization chamber (PTW 30013 Farmer type and PTW 31016 Pinpoint 3D) were measured under the same conditions. Results: Differences between the point dose with RPL glass dosimeter and that with Pinpoint 3D chamber agreed within 2% at all positions (high and low dose regions). Point dose differences between with Farmer chamber and with Pinpoint 3D chamber agreed within 1% at target (high dose region). At OAR (low dose and steep dose gradient region), however, the dose difference was exceeded by 5%. This is due to volume averaging effect of Farmer chamber.Conclusion: Feasibility study of IMRT postal audit phantom was performed. The measurement dose with RPL glass dosimeter was good agreement with Pinpoint 3D ionization chamber. Therefore, the dedicated phantom using RPL glass dosimeter shows considerable potential for the IMRT postal audit. To establish IMRT postal audit in Japan, we are starting dummy run now.