Session

Overview: In proton therapy, a fixed relative biological effectiveness (RBE) of 1.1 is used worldwide for all fraction sizes and all tumor sites. However, recent experimental data show that the RBE increases significantly towards the distal edge of the treatment field, and several models parameterize the RBE as a function of linear energy transfer (LET). Clinically, an increased RBE may have detrimental effects on normal tissue; however, the clinical evidence for this is still limited. The use of variable RBE in proton therapy is therefore controversial. After a brief introduction, the present status, possible clinical implications and strategies will be discussed.