ABSTRACT
PURPOSE: Three-dimensional radiation dosimetry using magnetic resonance imaging of polymer gel was recently introduced. This dosimetry system is based on radiation induced chain polymerization of acrylic monomers in a muscle equivalent gel and provide accurate 3 dimensional dose distribution. We planned this study to evaluate the clinical value of this 3-dimensional dosimetry. MATERIALS AND METHODS: The polymer gel poured into a cylindrical glass flask and a spherical glass flask. The cylindrical test tubes were for dose response evaluation and the spherical flasks, which is comparable to the human head, were for isodose curves. T2 maps from MR images were calculated using software, IDL. Dose distributions have been displayed for dosimetry. The same spherical flask of gel and the same irradiation technique was used for film and TLD dosimetry and compared with each other. RESULTS: The R2 of the gel respond linearly with radiation doses in the range of 2 to 15 Gy. The repeated dosimetry of spherical gel showed the same isodose curves. These isodose curves were identical to dose distributions from treatment planning system especially high dose range. In addition, the gel dosimetry system showed comparable or superior results with the film and TLD dosimetry. CONCLUSION: The 3-dimensional dosimetry for conformal radiation therapy using MRI of polymer gel showed stable and accurate results. Although more studies are needed for convenient clinical application, it appears to be a useful tool for conformal radiation therapy.
Subject(s)
Humans , Glass , Head , Magnetic Resonance Imaging , Polymerization , Polymers , Radiometry , Radiotherapy, ConformalABSTRACT
PURPOSE: The wedge filter is the most commonly used beam modifying device during radiation therapy. Recently dynamic wedge technique is available through the computer controlled asymmetric collimator, independent jaw. But dosimetric characteristics of dynamic wedge technique is not well know. Therefore we evluate dosimetric characteristics of dynamic wedge compared to conventional fixed wedge. MATERIALS AND METHODS: We evaluated dosimetric characteristics of dynamic wedge and fixed wedge by ion chamber, film dosimetry and TLD in phantoms such as water, polystyrene and average breast phantom. Six MV x-ray was used in 15X15 cm field with 15,30 and 45 degree wedge of dynamic/fixed wedge system. Dosimetric characteristics are interpreted by wellhofer Dosimetrie system WP700/WP700i and contralateral breast dose(CBD) with tangential technique was confirmed by TLD. RESULTS: 1) Percent depth dose through the dynamic wedge technique in tissue equivalent phantom was similar to open field irradiation and there was no beam hardening effect compared to fixed wedge technique. 2) Isodose line composing wedge angle of dynamic wedge is more straight than hard wedge. And dynamic wedge technique was able to make any wedge angle on any depth and field size. 3) The contralateral breast dose in primary breast irradiation was reduced by dynamic wedge technique compared to fixed wedge. When the dynamic wedge technique was applied, the scatter dose was similar to that of open field irradiation. CONCLUSION: The dynamic wedge technique was superior to fixed wedge technique in dosimetric characteristics and may be more useful in the future.
Subject(s)
Breast , Film Dosimetry , Jaw , Polystyrenes , WaterABSTRACT
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.
Subject(s)
Alloys , Film Dosimetry , Pectinidae , Radiotherapy, ConformalABSTRACT
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.