Vol.5 No.4 2013

Research paper : Dose standards for safe and secure breast cancer screening (T. Tanaka et al.)−240−Synthesiology - English edition Vol.5 No.4 (2013) (4)The objective was set as the improvement of the reliability of the dose evaluation of mammography machines in medical practice. Therefore, development effort was made to create a dose standard with irradiation geometry close to the mammography machine, aiming for the reduction of the uncertainty of dose evaluation in medical practice.(5)Moreover, in standard dissemination, focus was placed on the glass dosimeter used in medical practice. Attempt was made to improve the reliability of dose evaluation of mammography machines by evaluating the glass dosimeters using AIST’s dose standard.Answer (Takahiro Tanaka)I revised the scenario diagram as you have indicated to clarify the characteristics of this research. Additionally, I have revised the arrangement of the chapters following chapter 4 to match the scenario diagram.8 Technological characteristics of the standard in this researchQuestion (Naoto Kobayashi)I ask the following questions for confirmation. Are the following reasons valid in terms of the difference from the conventional X-ray dose standard?(1)It is necessary to use low energy of about 30 keV instead of 80 keV to reduce the effect of radiation to the human body. Also, since the absorption per unit length (stopping power) of the X-rays within that energy range is greater than that of the medium energy X-rays, sufficient contrast can be obtained between the mammary tissues and the lesions. On the other hand, special measures must be taken because the precision of X-ray dose evaluation decreases for low energy X-rays.(2)Since an X-ray tube with a molybdenum target anode and a molybdenum filter are used for the mammography X-ray beam at around 30 keV, the energy spectrum approaches monochromatic, and the energy spectrum after absorption by substances is greatly different from the X-rays that use W/Al at around 80 keV.Answer (Takahiro Tanaka)I think your understanding is correct. To obtain sufficient contrast between the mammary tissues and lesions, an energy lower than that used in general radiography is needed for mammography. In the dosimetry of low-energy X-rays where the sensitivity of the dosimeter changes with the X-ray energy, the difference between the radiation qualities of general radiography X-rays and mammography X-rays affects the precision of the dose evaluation. The paper was revised to address the radiation quality of mammography X-rays.6 Outcome of this researchQuestion (Naoto Kobayashi)I will ask about the outcome of this research. Now that the standard for low-energy X-ray dose has been newly established and is being disseminated, what practical outcome do you expect? For example, do you expect that the increased reliability of mammography will make more people go to cancer screening? If that will not happen, what other efforts are needed for the further diffusion of mammography in society?Answer (Takahiro Tanaka)The reliability of mammography dose evaluation has increased owing to the development of this standard. The manufacturers of mammography machines are making efforts to develop machines with lower dosages and higher quality images. While this standard may not contribute to the improvement of image quality, I think it will contribute to a lower dose, because a dose standard is essential for quantitative dose evaluation.We have received several offers for joint research from the industry, universities, and academic societies, and we are currently working to increase the precision of mammography dose evaluation. In the future, I hope we can help to reduce the mammography dose using data obtained from joint research projects.7 Research goalsComment (Naoto Kobayashi)Initially, the diagram for the scenario in Fig. 4 showed only the establishment of the standard for general X-ray dosimetry and precision improvement. I don’t think it shows the scenario for the establishment and distribution of the mammography X-ray dose evaluation method that you described in this paper.I think there are the following characteristics in the mammography X-ray dose evaluation. Please add how they were positioned in the scenario, and present the diagram of the scenario for achieving your goal.(1)The existing soft X-ray standard (W/Al radiation quality) was used as the national standard, and the correction factors of the national standard were newly evaluated for the mammography X-ray radiation quality.(2)Although there is no technological novelty in (1), it was preliminarily confirmed using the Monte Carlo calculation that there would be no fatal effect on the measurement results and uncertainty.(3)Rather than developing a primary standard optimized for mammography radiation quality and aiming at high precision, importance was placed on the speed of standard establishment using the existing standard, even if precision was somewhat sacrificed. (This is an extremely important R&D strategy.)


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