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Dosimetric Comparison of Intensity Modulated Radiation Therapy (IMRT), 3D Conformal Proton Therapy and Intensity Modulated Proton Therapy (IMPT) for Metastatic Brain Cancer

M Sullivan*, S Ahmad, H Jin, University of Oklahoma Health Sciences Center, Oklahoma City, OK

Presentations

PO-GePV-T-103 (Sunday, 7/25/2021)   [Eastern Time (GMT-4)]

Purpose: To compare IMRT against proton treatment (conformal or IMPT) plans for metastatic brain cancer.

Methods: Ten IMRT patients with brain cancer were retrospectively chosen, all of which received doses in the range of 20 to 40 Gy and in 3 to 5 fractions by Varian TrueBeam STx. Three proton plans (conformal: double scattering, static-IMPT: single collimation, and dynamic-IMPT: layer-by-layer collimation) were generated for the same patient using Mevion S250 (conformal) and S250i (IMPT) to compare. Each plan had respective treatment planning systems: Brainlab iPlan for IMRT, Varian Eclipse for proton conformal, and RaySearch Raystation for IMPT. Dosimetric comparisons were carried out through dose-volume histogram analysis of the target and the organs at risk.

Results: Average target dose conformity indices are 2.42, 2.79, 2.25 and 2.30 and homogeneity indices are 1.61, 5.08, 8.05, and 9.07 for IMRT, proton conformal, static-IMPT and dynamic-IMPT, respectively. Average maximum target doses differ with respect to prescription dose by 1.19%, 5.2%, 8.19%, and 9.26% for IMRT, proton conformal, static-IMPT and dynamic-IMPT, respectively. Normal tissues are in general spared more on average with proton compared to photon treatments. The following percentages represent average maximum dose relative to prescription dose to the brainstem and optic chiasm, respectively. IMRT: 37.61% and 14.86%, Proton Conformal: 22.18% and 10.89%, IMPT Static: 28.12% and 12.93%, IMPT Dynamic: 27.27% and 14.08%.

Conclusion: Target dose homogeneity was better with IMRT compared to proton, whereas overall dose conformity was found somewhat better with IMPT than IMRT. Normal tissue doses were better for both conformal proton and IMPT compared to IMRT when the tissues are not in close proximity to the target.

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