Comparison of intensity-modulated radiation therapy (IMRT), 3D conformal proton therapy and intensity-modulated proton therapy (IMPT) for the treatment of metastatic brain cancer.

Abstract

The purpose of this study has been to compare photon intensity modulated radiation therapy (IMRT) against both conformal and intensity modulated proton therapy (IMPT) plans for metastatic brain cancer. Ten IMRT patients with brain cancer were chosen retrospectively, with prescription doses in the range of 20 to 40 Gy, delivered in 3 to 5 fractions using Varian TrueBeam STx machine. Three proton plans with proton double scattering, single collimation static-IMPT, and energy layer by layer collimation dynamic-IMPT were then generated for the same patients using the Mevion S250 system for conformal plans and the S250i system for IMPT plans. Each plan had respective treatment planning systems that include Brainlab iPlan for IMRT, Varian Eclipse for proton double scattering, and RaySearch Raystation for IMPT. Dosimetric and radiobiologic comparisons were made through dose-volume histogram (DVH) analysis of the target and the organs at risk (OAR); and with parameters of equivalent uniform dose (EUD), tumor control probability (TCP), and normal tissue complication probability (NTCP), respectively. A set of variables α/β ratio, survival fraction, and clonogenic cell density were selected and varied to observe their effect on the abovementioned parameters. Doses were observed to be more homogeneous for patients with brain malignancies with photon IMRT treatments, while dose conformity is improved with proton PBS treatments. Normal tissue is, on average, spared more through both proton treatment options. The minimum doses, closely approximated by dose to 98% of the target volume, are similar across treatment modalities with slight variations.