Program Information
Evaluation of the Alignment Stability in Clip-Based Ocular Proton Treatments by Comparison of Pre and Post-Treatment Radiographs
E Kryck*, R Slopsema , M Mamalui , D Yeung, M Bennett, R Dagan, M Rutenberg, Z Li , The Univ of Florida Health Proton Therapy Instit., Jacksonville, FL
Presentations
WE-RAM2-GePD-J(B)-5 (Wednesday, August 2, 2017) 10:00 AM - 10:30 AM Room: Joint Imaging-Therapy ePoster Lounge - B
Purpose: To evaluate the stability of the eye during clip-based ocular proton therapy treatments.
Methods: Patients treated for ocular melanoma with proton therapy had small metal clips placed on the external surface of the eye (sclera) for target delineation and target alignment. After patient immobilization, orthogonal radiographs displaying the clips were used to align the patient before radiation. Radiographs were also taken after irradiation to verify that the position was correct during treatment. 54 pre and post-treatment radiographs were retrospectively reviewed to determine the alignment stability. First, the 3D clip positions were calculated from orthogonal radiographs. Then the shift (translation and rotation) was determined between the pre and post-treatment clip positions using the rigid transformation.
Results: For 48 treatments, the maximum shift between pre and post-treatment radiographs is less than 1mm. The average shift is less than 0.05mm with a standard deviation of 0.3mm. The maximum rotation is less than 1 degree in each axis, with an average less than 0.5 degrees and a standard deviation of 0.5 degrees. The root-mean square error (RMSE) was less than 0.25mm for all cases; although it was much lower for treatments where more than 2 clips were able to be localized. 6 treatments were unable to be analyzed with certainty due to only 1 clip being able to be localized; these treatments were not used for statistical analysis.
Conclusion: Patient alignment is stable when using clip-based alignment systems for ocular proton therapy, although more than 2 clips are required for optimal results.
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