ABSTRACT
Various metal screen-film combinations have been investigated in order to determine the best radiographic image. The quality of these different combinations has been evaluated by measuring the scattered to primary film dose ratio S/P. The S/P ratio increases with increasing atomic number of the front screen for 4 MV x-rays but shows no significant difference for 8 MV x-rays. For rear screens the S/P ratio is slightly increased for higher atomic numbers. A metal with an atomic number around 26-29 should be an optimal metal screen regarding quality aspects. A cassette of stainless steel has, in clinical use for portal and/or verification films, given very good images.
Subject(s)
Radiographic Image Enhancement/methods , Radiotherapy, High-Energy/methods , X-Ray Intensifying Screens , Humans , Radiotherapy Dosage , Radiotherapy, High-Energy/instrumentation , Scattering, RadiationABSTRACT
A specially designed cassette which gives an excellent quality of portal films has been used to determine the set-up accuracy and uncertainties in treatment alignment during full-course radiation therapy on patients treated for some common malignant diseases. An analysis of a comparison between simulator films and portal films is also presented. For various diagnoses treatment-to-treatment positioning varied with an average standard deviation of 3.5 mm despite the use of laser alignment and good patient fixation.
