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Credentialing of IGRT Equipment and Processes for Clinical Trials

L Court

L Court1*, M Aristophanous1 , D Bellezza2 , D Followill1 , S Kirsner1 , K Kisling1 , B Massingill3 , N Papanikolaou4 , B Parker5 , R Pidikiti1 , P Wong1 , H Zhen6 , P Balter1 , (1) UT MD Anderson Cancer Center, Houston, TX, (2) St. Luke's Radiation Therapy, Houston, TX, (3) Scott & White, Temple, TX, (4) University of Texas HSC SA, San Antonio, TX, (5) Univ Texas Medical Branch of Galveston, Galveston, TX, (6) UT Southwestern Medical Center, Dallas, TX


SU-E-J-189 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose: Current dosimetry phantoms used for clinical trial credentialing do not directly assess IGRT processes. This work evaluates a custom-built IGRT phantom for credentialing of multiple IGRT modalities and processes.

Methods: An IGRT phantom was built out of a low-density body with two inserts. Insert A is used for the CT simulation. Insert B is used for the actual treatment. The inserts contain identical targets in different locations. Relative positions are unknown to the user. The user simulates the phantom (with insert A) as they would a patient, including marking the phantom. A treatment plan is created and sent to the treatment unit. The phantom (with insert B) is then positioned using local IGRT practice. Shifts (planned isocenter, if applicable, and final isocenter) are marked on the phantom using room lasers. The mechanical reproducibility of re-inserting the inserts within the phantom body was tested using repeat high-resolution CT scans. The phantom was tested at 7 centers, selected to include a wide variety of imaging equipment.

Results: Mechanical reproducibility was measured as 0.5-0.9mm, depending on the direction. Approaches tested to mark (and transfer) simulation isocenter included lasers, fiducials and reflective markers. IGRT approaches included kV imaging (Varian Trilogy, Brainlab ExacTrac), kV CT (CT-on-rails), kV CBCT (Varian Trilogy, Varian Truebeam, Elekta Agility) and MV CT (Tomotherapy). Users were able to successfully use this phantom for all combinations of equipment and processes. IGRT-based shifts agreed with the truth within 0.8mm, 0.8mm and 1.9mm in the LR, AP, and SI directions, respectively.

Conclusion: Based on these preliminary results, the IGRT phantom can be used for credentialing of clinical trials with an action level of 1mm in AP and LR directions, and 2mm in the SI direction, consistent with TG142. We are currently testing with additional institutions with different equipment and processes, including Cyberknife.

Funding Support, Disclosures, and Conflict of Interest: This project was funded by the Cancer Prevention Research Institute of Texas

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