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Dosimetric Comparison of 2D and 3D Episcleral Plaque Treatment Planning

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B Dapaah-Afriyie

B Dapaah-Afriyie1*, D Wilkinson2 , M Astrahan3 , A Singh4 , J Berry5 , (1) Cleveland State University, Cleveland, OH, (2) Cleveland Clinic Foundation, Cleveland, OH, (3) University of Southern California, Los Angeles, CA, (4) Cleveland Clinic Foundation, Cleveland, OH, (5) University of Southern California, Los Angeles, CA


MO-RPM-GePD-TT-3 (Monday, July 31, 2017) 3:45 PM - 4:15 PM Room: Therapy ePoster Theater

Purpose: To conduct a dosimetric comparison of 2D (US plus visualization) and 3D (US and CT or MRI) episcleral plaque treatment plans to assess the value of adding ophthalmic CT imaging in the treatment planning process.

Methods: TPS Plaque Simulator v6 (PS6) was used to replicate treatment plans for patients who had undergone multiple imaging modalities for modeling of ocular anatomies and plaque treatments. Each patient received CT scans that served to register the actual curvature of the eye in PS6 and these plans were replicated without CT image registration. Replicated plans were normalized to original treatment time, prescription dose and plaque location (e.g., 168 hours, 85 Gray to the tumor apex, plaque centered on apex). Doses to critical structures were then compared.

Results: Data analysis of the 46 paired plans via a Wilcoxon signed-rank test showed that a significant dosimetric difference exists between the original plans and the re-plans, in the optic, opposite retina and lens doses. However, the doses to the fovea and the sclera did not exhibit significant differences.

Conclusion: The results of this work indicate that CT image registration may provide different dose estimates for critical eye structures compared to the standard PS6 tumor model. This is likely related to the better conformality of the dose to the shape of the target (e.g., fewer sources closer to the optic disc in certain cases). However, despite these observed differences, more data are required prior to a switch to 3D planning. Further investigation between the plans would consist of comparing the episcleral equivalent of a DVH, the retina dose area histogram (RDAH).

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