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Film dosimetry is a convenient and quick method of obtaining a set of highenergy radiation isodose curves in the plane of the film, but it is un empirical methods which presents some problems. Many authors have reported on film dosimetry for industrial films. Recently, the development of computerized densitometor systems, ready-pack films for rediotherapy and automatic film processors has helped improve the procedure. This paper reports our experiences regarding film dosimetry using the new materials, its usefulness in radiotherapy and some of technical problems encountered. The optical density varlue corresponding to a given dose depends upon the processing conditions, for XV-2 film, variation is about 4% when an automaticprocessor is used under controlled conditions. The Off-axis-ratios and the PDD in the perpendicular film plane agree well with the ion-chamber for photon and electron beams;by contrast, the PDD in the parallel film plane is significantly affected by variations in the phantom thickness, the type of film package and misalignment in phantom. But bare films inserted into a cassette made of phantom material agree well for electron beams. Film dosimetry is effective and accurate at the edges of the field and for small fields, due to its high spatial resolution and rapid method. In addition, is usefull for electron beams OCR beam data input;for evaluating the input parameters for treatment planning systems;for quality assurance of the treatment equipment;and for preliminary clinical studies. Even when modern materials are used for film dosimetry, some technical probrems will arise. Thus, to ensure the accuracy, certain precautions are required when setting conditions of film exposure and for quality control of the film processor.
