Portal films for relative exit dose determinations.

Abstract

Portal films are radiographic images taken regularly in external photon beam radiotherapy in order to verify geometrical set-up. However, they also contain quantitative dose information. Absolute dosimetry with film is possible but the desired accuracy of +/- 5% is difficult to achieve. However, relative dosimetry with film would be useful in combination with a point determination of absolute dose, though a dose response linearisation is required for relative dosimetry over the range of doses given to portal films in routine clinical practice. For this purpose, a technique for the rapid dose response linearisation of portal films is investigated in simulated treatment situations and evaluate..