UCLA

In regard to our recently published paper entitled "Treatment planning comparison of IMPT, VMAT and 4π radiotherapy for prostate cases", a question was raised whether "4π" was used appropriately to describe the non-coplanar planning and delivery space. In this letter, the term use is explained from both theoretical and practical perspectives. It is concluded that the self-explanatory term provides a flexible description of non-coplanar radiotherapy with beam orientation optimization. Confusions with this term can be avoided by understanding the evolving and machine/patient specific nature of 4π planning.