Technical topics in radiotherapy over past two decades are discussed to evaluate the role of medical imaging and information sciences in radiotherapy. The information obtained by CT simulator system is the standard of the radiotherapy treatment planning. It has been based on anatomical objects, and clinicians should specify the target volumes and risk organs following the recommendation of ICRU Reports 50 and 62. The PTVs must ensure proper coverage of the CTVs in the presence of interfraction and intrafraction variation of treatment setup and organ motion.
There is a basic concept that increasing precision and accuracy in radiation delivery will lead to reduced toxicity with potential for dose escalation and improved tumor control. The accuracy of patient immobilization and placement system is critical to accurate dose delivery and marginal volume. The accuracy of daily treatment has become crucial especially with the introduction of dose escalation and sophisticated technique such as STI（stereotactic irradiation）and IMRT（intensity modurated radiation therapy）.
STI is the 3‐dimensional hypofractionated radiotherapy that delivers larger fraction doses more precisely than standardly fractionated radiation. The technique of IMRT is very analogous to the tomography technique used for CT. Using non‐uniform and customized fluence distributions in the treatment delivery, high‐dose region is shaped to conform to the geometry to the target in three dimensions with rapid fall in all directions outside the target volume. There is a need for image guidance to achieve the benefits of modern irradiation and IGRT（image guided radiation therapy）has been introduced in clinic. IGRT is a term that has been applied to the use of various imaging technologies in both the planning and the execution of radiation treatment in order to adjust the field to the position of the target as detected by each imaging procedure.
The radiation treatment system has acquired the high accuracy which largely relies on the medical imaging and information sciences. The demand of your participation in radiotherapy is increasing.

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In recent years, there is a growing demand for the accountability of those who manage to reduce patient dose for x‐ray imaging to the necessary minimum. Following the concept of ALARA（as low as reasonably achievable）, radiologists and physicists will need to work collaboratively to determine the appropriate image quality for diagnostic x‐ray imaging. The analysis and understanding of results of x‐ray imaging require an understanding of photon attenuation in matter. With this goal in mind, a discussion of photon attenuation in matter is given and related to those behavior to x‐ray imaging parameter, especially in the case of tube voltage dependency for polychromatic beam. Simulation studies were carried out to find the optimal tube voltage for the signal‐to‐noise ratio in projection imaging and computed tomography with polychromatic x‐ray source. In addition, material decomposition using dual‐energy CT reconstruction is introduced for relating linear attenuation coefficient to tissue composition and structure.

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The ratio of mammary gland in the breast is useful information for the risk analysis of breast cancer. In this study, we proposed the novel automated measurement technique of the mammary gland ratio in mammogram. It employed Gabor filter in order to detect the mammary gland in mammogram. Filtered image was binarized by automated thresholding method; mammary region was segmented. In the experiments, we calculated Jaccard index to evaluate the degree of coincidence between the detected mammary region and sketched mammary region drawn by radiologist. Subsequently, accuracy of mammary gland ratio was evaluated. Measurement error of mammary gland ratio was 4.9%, and mean Jaccard index was 78.31%; they were better than those of conventional method. These results indicate that proposed method may be useful for the automated analysis of mammary gland for risk analysis of breast cancer.

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It is desired to develop a computer‐aided detection system that automatically detects carotid artery calcifications（CACs）on dental panoramic radiographs（DPRs）. In our previous study, an automated method for the detection of CACs was proposed, in which the sensitivity of CAC detection was 90 % with 4.6 false positives（FPs）per image. We noticed that the regions of interest（ROIs）determined automatically as possible carotid artery regions by our previous scheme were relatively larger than those estimated by a dental radiologist. In this paper, we verified the necessity of an introduction of appropriate size and location of ROIs which are similar with those by the dental radiologist. We found that the sensitivity was maintained along with those appropriate ROIs, but the number of FPs per image was reduced to 0.9 using 100 DPRs. This result indicates that it is possible to reduce the number of FPs by accurately tailoring ROIs to individual cases.

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