Language：Japanese   Publisher：Japan Society of Medical Physics  

DOI： 10.11323/jjmp.41.4_195

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Other Link： http://id.ndl.go.jp/bib/030405007

Language：Japanese   Publisher：Japanese Society of Radiological Technology  

In X-ray therapy, equivalent square field (side of equivalent square field) is important because it influences the accuracy of independent verification of monitor unit (MU) by calculation. To calculate the side of equivalent square field for rectangular fields, we often use a table of domestic standard measurement method (Day’s method), or A/P method calculated by area-perimeter ratio. The sides of equivalent square fields of these methods are assumed to be unchanged by depth and energy, but there are reports that it is not valid. Therefore, the depth dependency of side of equivalent square fields of Day’s method, A/P method, and area ratio correction (ARC) method was compared by measuring phantom scatter factors (<i>S</i>_p). From the analysis of <i>S</i>_p measured at different depths, the estimated value of <i>S</i>_p on the equivalent square side of the Day’s method and A/P method had a depth dependency that the difference from the measured value was large when the measurement depth was deep. The estimated value of <i>S</i>_p on the equivalent square side of the ARC method had a small difference from the measured value even when the measurement depth was deep, and the depth dependency was small compared with the Day’s method and the A/P method. Side of equivalent square field of ARC method had a smaller difference of depth dependency than in the case of Day’s method and A/P method. Therefore, in the independent verification of MU for rectangular field, using the equivalent square side of the ARC method is better.

DOI： 10.6009/jjrt.2019_jsrt_75.6.525

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Other Link： http://id.ndl.go.jp/bib/029809937

Language：Japanese   Publisher：Japanese Society of Radiological Technology  

In monitor unit (MU) independent verification by calculation for irregular field (MLC field) using multileaf collimator in X-ray therapy, it has become common to use collimator scatter factor (<i>S</i>_c) and phantom scatter factor (<i>S</i>_p) instead of total scatter factor (<i>S</i>_{c, p}). It is usually expressed as <i>S</i>_{c, p} (<i>A</i>)=<i>S</i>_c (<i>A</i>)×<i>S</i>_p (<i>A</i>), and the field size <i>A</i> is considered but the depth <i>d</i> is not. <i>S</i>_c is data of in-air output, and measure with a mini-phantom at constant depth to remove electron contamination. On the other hand, <i>S</i>_p is obtained from measurement data of <i>S</i>_{c, p} and <i>S</i>_c, and can be expressed as <i>S</i>_{c, p} (<i>d</i>, <i>A</i>)=<i>S</i>_c (constant depth, <i>A</i>)×<i>S</i>_p (<i>d</i>, <i>A</i>) at an arbitrary depth <i>d</i>, thus <i>S</i>_p depends on the depth of <i>S</i>_{c, p}. Therefore, <i>S</i>_p needs to consider depth. In addition, a linear accelerator equipped with the tertiary MLC has two field sizes, that are collimator field by upper and lower collimators and MLC field by tertiary MLC below them. In MU independent verification by calculation, it is often used that the estimated value of <i>S</i>_p obtained by converting MLC field to equivalent square field and referring to data of <i>S</i>_p in square field. To convert the MLC field to equivalent square field, a conversion formula from sector radius <i>r</i> to equivalent square field <i>L</i> by Clarkson’s sector integration (Clarkson method) is used. In this study, using 24 types of MLC fields to evaluate estimation accuracy due to the difference of conversion formula in Clarkson method, we estimated value of <i>S</i>_p using <i>r</i>=0.5611<i>L</i> of B-Clarkson method and using <i>r</i>=0.5580<i>L</i> of A-Clarkson method. And the difference with the measured value of <i>S</i>_p obtained by measuring <i>S</i>_{c, p} and <i>S</i>_c in the same MLC fields was compared. While, to evaluate estimation accuracy due to the different depths using these Clarkson methods, the difference between estimated value and measured value of <i>S</i>_p similarly obtained at depth of 5, 10 and 15 cm was compared. As results, estimated value of <i>S</i>_p using A-Clarkson method than using B-Clarkson method was close to measured value, and it was the same trend at depth of 5, 10 and 15 cm. Therefore, it was suggested that estimation accuracy of <i>S</i>_p by A-Clarkson method is higher than B-Clarkson method when verifying beams with different depths in MU independent verification by calculation for MLC field.

DOI： 10.6009/jjrt.2019_jsrt_75.12.1426

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Other Link： http://id.ndl.go.jp/bib/030183658

Language：Japanese   Publisher：Japanese Society of Radiological Technology  

Countermeasures against respiratory movement are important for tumors of thorax and abdomen in stereotactic body radiation therapy. In the present paper, a web-camera-based-respiratory monitoring method without contact with patient’s body was proposed for respiratory study. Thoracic and abdominal motion images were taken by a web camera, and were analyzed using simple image-processing techniques for obtaining respiratory waveforms. Four motion images with different respiration rate were obtained from resusci anne simulator. Respiration waveforms were estimated from the moving images by the proposed method, and were compared with respiration waveforms obtained by the conventional respiratory monitoring device. That was found to have a strong correlation. In addition, the two waveforms were similar in Bland–Altman method comparison. The proposed method can provide non-contact, non-invasive, simple, and realistic respiratory monitoring system for radiotherapy.

DOI： 10.6009/jjrt.2018_jsrt_74.11.1286

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Other Link： http://id.ndl.go.jp/bib/029359646