原体照射法の技術と応用

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In radiotherapy it is very important that the modalities of treatment must be chosen to give the maximum dose homogeneously to the malignant tumor with the minimal dose to the sorounding normal tissues. Conformation radiotherapy has been developed as one of the reasonable techniques of the external radiation treatment. It is aimed at irradiating the deformed tumor selectively, and at reducing the unnecessary irradiation given to sorrounding normal structures to a negligible extent at the same time. In this report, the outline of the historical development of this mechanism, the results of the basic experiment and the practical problems of conformation technique in daily work were described. Conformation radiotherapy was named by Prof.S.Takahashi in 1961,and its technique was applied to the treatment of cancer of the uterine cervix at first. For thee years after that, two cobalt units with conformation device were installed at two hospitals in Nagoya. In 1966,the 6 MeV linear accelerator with more precise conformation mechanism was installed, and since then the application of conformation technique became easier in routine work. The routine operation of conformation mechanism begins with setting the cams made of bakelite sheet. When the cams and the source rotate synchronously, diaphragms are set in opening-closing motion during rotation. As the result, the high dose region proportional to the cam contours is formed at the position of the rotatory center. The dose distributions, the dose variations on rotation axis and the method of calculating the central dose were confirmed by phantom experiments on 6 MeV X-ray, and the various types of dose distribution of irregular target-volume required for clinical purposes were measured. High dose regions were sufficiently conformed to the expected target volume, and the deformation of the dose distributions was negligible even in homogeneous phantom (cork in mix-D phantom). Dose variation along the rotational axis was 5 percent at the most. As for the method of dose calculation, the calculated value agree with experimental results within the range of the experimental error. The treatment lesions to which the conformation technique applies in our hospital, are carc. of the maxillary sinus, the esophagus and the uterine cervix. About 60% of these cases are treated with the conformation technique. For the treatment of carc. of the maxillary sinus the selective protection of the both-sided lens was combined with field-shaping technique. The influence of the metal absorber to the dose of rotation axis and the dose distribution were measured, and the method of correction for these problems were also investigated. In case of carc. of the esophaqus the calculated dose values on rotation axis in each transverse section were compared. Dose variation along the rotation axis was measured by phantom experiments and an efficient method of estimation of central dose was shown. Conformation technique modified to irradiate concaved target lesion in case of the whole pelvis irradiation was described, and was compared with the selective hollow-out technique. It was revealed that the application of the isotime curves was simple and would be useful in estimating actual isodose curves for each expected target volume. In the last section, the differences between two conformation systems, the mechanical problems of multi-sectional diaphragms, and the check-up method and MTBF of these mechanisms were discussed. Being able to conform a high dose region to the deep seated lesion in human body, conformation technique seems superior to the othermethods. No particular differences are recognized on the method of tumor localization, the dose estimation, the technique of set-up and so on. As the computed tomography has been able to give an exact representation and quslification of internal structure, the conformation technique will provide more accurate radiation treatment connected with these computer system near in f
公益社団法人日本放射線技術学会の論文
1976-09-01

原体照射法の技術と応用

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