Calculation of complication probability of pion treatment at paul scherrer institute using dose‐volume histograms

Abstract

AbstractIn conformation radiotherapy a target is irradiated uniformly, whereas surrounding organs receive non‐uniform radiation. Clinical data concerning complications with conventional radiation are not applicable there without appropriate compensation. A solution was proposed by Lyman [Int J Radiat Oncol Biol Phys 13:103–109, 1987 and 17:433–436, 1989; Radiat Res Suppl 8:13–19, 1985] using dose‐volume histograms. It reduces a given histogram to a single step which corresponds to the equivalent complication probability. It converts non‐uniform radiation into a unique dose to the whole organ which has the equivalent complication probability. This method was applied to actual patients treated by pion conformation technique at Paul Scherrer Institute (PSI). Of 90 pelvic tumors, 16 developed grade III‐TV bladder injury and 7 developed grade III‐IV rectal injury. The 90 cases were divided into roughly equal groups according to the equivalent doses to the entire bladder and rectum. Observed complication rates and the equivalent doses to the full organs in these groups could be represented by a sigmoid dose‐effect relation. When the relative biological effectiveness (RBE) is assumed to be 2.1 for bladder injury, the observed complication rates of the bladder fit best to the theoretical curve. When the RBE value is 2.3, the rates of rectal injury fit best. These values are close to the conversion factor of 2.0 used in clinical practice. This agreement suggests the feasibility of the method. © 1993 Wiley‐Liss, Inc.