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  5. A Retrospective Comparison of TG-43 Calculated and Heterogeneity-Corrected Dose Distributions for 125I COMS Eye Plaques

A Retrospective Comparison of TG-43 Calculated and Heterogeneity-Corrected Dose Distributions for 125I COMS Eye Plaques

S Simiele*, A Choi , H Cho , C Lee , University of Michigan, Ann Arbor, MI

Presentations

(Tuesday, 7/31/2018) 10:30 AM - 11:00 AM

Room: Exhibit Hall | Forum 3

Purpose: To evaluate the differences in TG-43-calculated and heterogeneity-corrected dose distributions to different organs at risk (OAR) and the prescription (Rx) point for 126 eye plaque (EP) treatments. Additionally, the dependency of the range of dose differences on tumor dimensions and locations was assessed.

Methods: Plaque Simulator (v6.4.7) was used to calculate EP dose at a single institution for tumors treated from 2013 – 2016. All treatments were performed using IsoAid pre-loaded EP ranging in diameter from 12–22 mm. Data was evaluated for laterality, frequency of use for different EP diameters, and tumor size. Dose calculations for patient treatments were performed using the TG-43 dosimetry formalism. Retrospective dose calculations were performed to assess the impact of heterogeneity corrections on the dose to OAR and the Rx point. Differences in dose to relevant OAR and the Rx point were calculated between the two dose calculation methods. The spread of differences between the two calculation methods was evaluated for correlation with tumor size and location.

Results: 50.8% of the tumors presented in the left eye and 49.2% presented in the right eye. The 16 mm EP was most frequently used. Tumors ranged in height from 1.0–12.5 mm. Heterogeneity-corrections resulted in a reduced dose to the Rx point with the magnitude of the reduction being a function of the size of the EP and the height of the tumor. The difference in dose to the eye origin was constant across all plaque sizes due to the constant treatment geometry.

Conclusion: Correlations were found between the differences in dose calculated using TG-43 and heterogeneity-corrected dose distributions and the size or the location of the tumor for specific OAR. This information can be useful for physicists and clinicians in estimating the heterogeneity-corrected dose to OAR, data that is not provided in TG-129.

Keywords

I-125, Eye Plaques, Brachytherapy

Taxonomy

TH- Brachytherapy: General (most aspects)

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