iPlan RT is described as 'The increasing need for higher dose delivery per fraction continues with trends towards Hyperfractionation and SBRT'. There are three alternatives to iPlan RT for Windows and Linux. The best alternative is XiO. It's not free, so if you're looking for a free alternative, you could try matRad.
With sophisticated automation and a flexible client-server architecture, XiO empowers clinicians to develop precise treatment plans in an efficient clinical environment. XiO delivers rapid and reliable registration of multiple data sets with automated image fusion.
Eclipse™ is a comprehensive treatment planning system that simplifies modern radiation therapy planning for all kinds of treatment, including 3D conformal, intensity-modulated radiation therapy (IMRT), electron, proton, and brachytherapy.
matRad is an open source software for radiation treatment planning of intensity-modulated photon, proton, and carbon ion therapy. matRad is developed for educational and research purposes; it is entirely written in MATLAB.