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Dosimetric Comparison of Volumetric Modulated Arc Therapy (VMAT), 3D Conformal Proton Therapy and Intensity Modulated Proton Therapy (IMPT) for Lung Cancer

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

Presentations

PO-GePV-T-104 (Sunday, 7/25/2021)   [Eastern Time (GMT-4)]

Purpose: To compare VMAT against proton treatment (conformal and IMPT) plans for lung cancer.

Methods: Ten patients with lung cancer were retrospectively chosen, each of which received doses of 55 Gy in 5 fractions using 6X photon beam from Varian TrueBeam STx machine with VMAT technique. The treatment plans were done using Varian Eclipse treatment planning system (TPS). Two proton treatment plans (conformal: double scattering, and static-IMPT) were subsequently generated for each patient using Mevion S250 and Mevion S250i for conformal and IMPT, respectively. Varian Eclipse TPS was used for proton conformal, and RaySearch Raystation was used for IMPT. Dosimetric comparisons were carried out through dose-volume histogram analysis of the target volume and the organs at risk.

Results: Average target dose conformity indices are 2.90, 2.70, and 2.0 and homogeneity indices are 3.2, 6.1, and 11.4 for VMAT, proton conformal and static-IMPT, respectively. Average maximum target doses differ with respect to prescription dose by 6.8%, 9.1%, and 13.3% for VMAT, proton conformal, and static-IMPT, respectively. Normal tissues are in general spared more on average with proton treatments when compared to photon treatments. The following percentages represent average maximum dose relative to prescription dose to the spinal cord, uninvolved lung, and heart, respectively. VMAT: 15.8%, 20.6%, and 15.5%; Proton Conformal: 3.3%, 5.2%, and 15.1%; and IMPT: 6.1%, 5.3%, and 12.3%.

Conclusion: Target dose homogeneity was better with VMAT compared to proton treatments, whereas overall dose conformity was found to be somewhat better with IMPT than proton conformal and VMAT. Normal tissue doses were better for both conformal proton and IMPT compared to VMAT, with IMPT being the best.

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