Comments on 'Single-Arc IMRT?'

We read with interest the article titled 'Single-Arc IMRT?' (Bortfeld and Webb 2009 Phys. Med. Biol. 54 N9-20) and feel it imperative to draw the attention of your readers to comments suggesting that the authors may not be fully aware of current developments in this field. As their paper was first submitted on 19th of August 2008, it could not have taken into account data presented at the AAPM, ESTRO and ASTRO meetings in 2008. In this letter, we would like to clarify some relevant aspects of RapidArc (Varian Medical Systems) as a modality for delivering single-arc treatment. (letter to the editor)