Purpose: The purpose of this study was to investigate the status of the implementation of quality assurance (QA) for intensity-modulated radiation therapy (IMRT) in Japan using a questionnaire survey.
Methods: The questionnaire consisted of seven sections: (1) clinical uses of IMRT, (2) treatment planning systems, treatment machines, phantoms for verification and CT scanning, (3) absorbed dose verification, (4) dose distribution verification, (5) fluence map verification, (6) acceptance criteria for each verification, and (7) comments.
Results: The questionnaire was completed by 129 institutions (response rate: 76.8%). IMRT was performed for prostate cancer in 125 institutions (96.9%), followed by head and neck cancer in 83 (64.3%), and brain tumors in 69 (53.5%). Although at least three individuals were engaged in IMRT QA in 77.5% of the institutions, the number of full-time persons involved in IMRT QA was one or less in 94 institutions (72.9%). This indicated that most institutions in Japan have a staff shortage. More than 90% of the institutions verified both the absorbed dose and dose distribution. The acceptance criterion for the absorbed dose verification was set to ±3% in at least 80% of the institutions. Gafchromic film was used for the majority of dose distribution verifications. The acceptance criteria for dose distribution verification mainly involved gamma analysis and a comparison of dose profiles; however, the judgment of acceptance did not depend on the results of the gamma analysis.
Conclusion: This survey increases our understanding of how institutions currently perform IMRT QA analysis. This understanding will help to move institutions toward more standardization of IMRT QA in Japan.

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A new definition of risk is that risk is the product of a measure of the size of the hazard and its probability of occurrence. We have some mechanisms that would be make too perception of risk in our mind. These mechanisms are including information processing of risk, binary judgment, and risk perception of low probability area. We are required to have bidirectional communication with other person. So, in order to do good risk communication, we have to establish a trust relationship with other person.

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Utilization of differential equations and methods for solving them in medical physics are presented. First, the basic concept and the kinds of differential equations were overviewed. Second, separable differential equations and well-known first-order and second-order differential equations were introduced, and the methods for solving them were described together with several examples.
In the next issue, the symbolic and series expansion methods for solving differential equations will be mainly introduced.

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