[Pin-hole camera studies of the head scatter contribution and the photon source size of a linear accelerator]

There are different opinions of the jaws scatter contribution to the photon fluence of medical linear accelerators. Investigations were performed at the Radiology Clinic of the University of Jena to give an experimental answer to this question. Since the study object was the linear accelerator LUE, now out of operation, the method of investigation is was the topic of this report. By use of a pin-hole camera and a "beam stopper", the focal and extrafocal radiation was projected upon the image plane of the camera and was measured with films or a Schuster detector array. The following relative contributions of the particular source regions to the total photon fluence in the field center were obtained: flattening filter (91.8 +/- 1)%, primary collimator (7.2 +/- 0.9)%, collimator jaws (1.0 +/- 0.3)%. These results are in good agreement with those of Ahnesjö. For this accelerator, the 37% width of the photon source region is (20 +/- 1) mm.