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J Korean Soc Ther Radiol. 1995 Dec;13(4):391-396. Korean. Original Article.
Lee SW , Oh YT , Kim WC , Keum KC , Yoon SI , Kim HS , Park W , Chu SS , Kim GE .
Department of Radiation Oncology, Yonsei University College of Medicine, Seoul, Korea.
Yonsei Cancer Center, Yonsei University College of Medicine, Seoul, Korea.

PURPOSE: The Conformal Radiation Therapy has been widely used under favour of development of computer technologies. The delivery of a large number of static radiation fields are being necessary for the conformal irradiation. In this paper, we investigate dosimetric characteristics on penumbra regions of a multileaf collimator(MLC), and compare to those of lead alloy block for he optimal use of the system in 3-D conformal radiotherapy. MATERIALS AND METHODS: The measurement of penumbra by MLC or lead alloy block was performed with 6 or 10 MV X-rays. The film was positioned at a dmax depth and 10 cm depth, and its optical density was determined using a scanning videodensitometer. The effective penumbra, the distance from 80% to 20% isodose lines and 90 to 10 were analyzed as a function of the angle between the direction of leaf motion and the edge defined by leaves. RESULTS: Increasing MLC angle (0-75degree) was observed with increasing the penumbra widths and the scalloping effect. There was no definite differences of penumbra width from 80% to 20% isodose lines, while being the small increase of penumbra width of lead alloy block are agree reasonably with those of MLC within 4.8mm. CONCLUSION: The comparative qualitative study of the penumbra between MLC and lead alloy block demonstrate the clinical acceptability and suitability of the multileaf collimator for 3-D conformal radiotherapy.

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