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  • Wiley  (3)
  • Igaki, Hiroshi  (3)
  • 1
    In: Journal of Applied Clinical Medical Physics, Wiley, Vol. 24, No. 5 ( 2023-05)
    Kurzfassung: We measure the dose distribution of gated delivery for different target motions and estimate the gating latency in a magnetic resonance‐guided radiotherapy (MRgRT) system. Method The dose distribution accuracy of the gated MRgRT system (MRIdian, Viewray) was investigated using an in‐house‐developed phantom that was compatible with the magnetic field and gating method. This phantom contains a simulated tumor and a radiochromic film (EBT3, Ashland, Inc.). To investigate the effect of the number of beam switching and target velocity on the dose distribution, two types of target motions were applied. One is that the target was periodically moved at a constant velocity of 5 mm/s with different pause times (0, 1, 3, 10, and 20 s) between the motions. During different pause times, different numbers of beams were switched on/off. The other one is that the target was moved at velocities of 3, 5, 8, and 10 mm/s without any pause (i.e., continuous motion). The gated method was applied to these motions at MRIdian, and the dose distributions in each condition were measured using films. To investigate the relation between target motion and dose distribution in the gating method, we compared the results of the gamma analysis of the calculated and measured dose distributions. Moreover, we analytically estimated the gating latencies from the dose distributions measured using films and the gamma analysis results. Results The gamma pass rate linearly decreased with increasing beam switching and target velocity. The overall gating latencies of beam‐hold and beam‐on were 0.51 ± 0.17 and 0.35 ± 0.05 s, respectively. Conclusions Film measurements highlighted the factors affecting the treatment accuracy of the gated MRgRT system. Our analytical approach, employing gamma analysis on films, can be used to estimate the overall latency of the gated MRgRT system.
    Materialart: Online-Ressource
    ISSN: 1526-9914 , 1526-9914
    URL: Issue
    Sprache: Englisch
    Verlag: Wiley
    Publikationsdatum: 2023
    ZDB Id: 2010347-5
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 2
    In: Medical Physics, Wiley, Vol. 48, No. 11 ( 2021-11), p. 7541-7551
    Kurzfassung: In this study, we report on our proposed phantom based on the new end‐to‐end (E2E) methodology and its results. In addition, we verify whether the proposed phantom can replace conventional phantoms. Methods The hexagonal‐shaped newly designed phantom has pockets on each side for a film dosimeter of size 80 × 90 mm 2 , which is easily removable, considering the 60 Co penumbra. The new phantom comprises water, shell, and auxiliary shell phantoms. The shell and auxiliary shell materials are Solid Water HE. A mock tumor (aluminum oxide) was attached by a single prop in the water phantom and placed at the center of the new phantom. The results of a conventional E2E test were compared with those of the novel E2E test using the newly designed phantom. The irradiated film dosimeter in the novel E2E test was scanned in a flatbed scanner and analyzed using an in‐house software developed with MATLAB. The irradiated field center, laser center, and mock tumor center were calculated. In the novel image‐matching E2E (IM‐E2E) test, image matching is performed by aligning the laser center with ruled lines. In the novel irradiation‐field E2E (IF‐E2E) test, the displacement of the irradiation‐field center was defined as its distance from the laser center. In the composite E2E test, the overall displacement, which included the accuracy of the irradiated field and image matching, was defined as the distance between the irradiated field center and mock tumor center. In addition, using the newly designed phantom, the overall irradiation accuracy of the machine was evaluated by calculating the three‐dimensional (3D) center of the irradiated field, phantom, and laser. The composite E2E test could be performed using the newly designed phantom only. Results In the IM‐E2E test, the results of the conventional and novel IM‐E2E tests were significantly different in each direction (left–right direction: p ‐value  〈   〈  0.05, anterior–posterior direction: p ‐value = 0.002, and superior–inferior direction: p ‐value = 0.002). The displacement directions were the same in both the conventional and novel IM‐E2E tests. In the analysis of the IF‐E2E test, no significant difference was evident between the results in each direction. Moreover, the displacement directions were the same in the conventional and novel IF‐E2E tests, except for the left–right lateral direction of head three. In addition, the 3D analysis results of the novel IF‐E2E test were less than 1 mm in all directions. In the analysis of the composite E2E test, the maximum displacement was 1.4 mm in all directions. In addition, almost all results of 3D analysis for the composite E2E test were less than 1 mm in all directions. Conclusion The newly designed E2E phantom simplifies the E2E test for MRIdian, and is a possible alternative to the conventional E2E test. Furthermore, we can perform the previously unfeasible composite E2E tests that include the entire treatment process.
    Materialart: Online-Ressource
    ISSN: 0094-2405 , 2473-4209
    URL: Issue
    Sprache: Englisch
    Verlag: Wiley
    Publikationsdatum: 2021
    ZDB Id: 1466421-5
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 3
    In: Medical Physics, Wiley, Vol. 50, No. 1 ( 2023-01), p. 424-439
    Kurzfassung: Boron Neutron Capture Therapy (BNCT) has recently been used in clinical oncology thanks to recent developments of accelerator‐based BNCT systems. Although there are some specific processes for BNCT, they have not yet been discussed in detail. Purpose The aim of this study is to provide comprehensive data on the risk of accelerator‐based BNCT system to institutions planning to implement an accelerator‐based BNCT system. Methods In this study, failure mode and effects analysis (FMEA) was performed based on a treatment process map prepared for the accelerator‐based BNCT system. A multidisciplinary team consisting of a medical doctor (MD), a registered nurse (RN), two medical physicists (MP), and three radiologic technologists (RT) identified the failure modes (FMs). Occurrence ( O ), severity ( S ), and detectability ( D ) were scored on a scale of 10, respectively. For each failure mode (FM), risk priority number (RPN ) was calculated by multiplying the values of O , S , and D , and it was then categorized as high risk, very high risk, and other. Additionally, FMs were statistically compared in terms of countermeasures, associated occupations, and whether or not they were the patient‐derived. Results The identified FMs for BNCT were 165 in which 30 and 17 FMs were classified as high risk and very high risk, respectively. Additionally, 71 FMs were accelerator‐based BNCT‐specific FMs in which 18 and 5 FMs were classified as high risk and very high risk, respectively. The FMs for which countermeasures were “Education” or “Confirmation” were statistically significantly higher for S than the others ( p  = 0.019). As the number of BNCT facilities is expected to increase, staff education is even more important. Comparing patient‐derived and other FMs, O tended to be higher in patient‐derived FMs. This could be because the non‐patient‐derived FMs included events that could be controlled by software, whereas the patient‐derived FMs were impossible to prevent and might also depend on the patient's condition. Alternatively, there were non‐patient‐derived FMs with higher D , which were difficult to detect mechanically and were classified as more than high risk. In O , significantly higher values ( p  = 0.096) were found for FMs from MD and RN associated with much patient intervention compared to FMs from MP and RT less patient intervention. Comparing conventional radiotherapy and accelerator‐based BNCT, although there were events with comparable risk in same FMs, there were also events with different risk in same FMs. They could be related to differences in the physical characteristics of the two modalities. Conclusions This study is the first report for conducting a risk analysis for BNCT using FMEA. Thus, this study provides comprehensive data needed for quality assurance/quality control (QA/QC) in the treatment process for facilities considering the implementation of accelerator‐based BNCT in the future. Because many BNCT‐specific risks were discussed, it is important to understand the characteristics of BNCT and to take adequate measures in advance. If the effects of all FMs and countermeasures are discussed by multidisciplinary team, it will be possible to take countermeasures against individual FMs from many perspectives and provide BNCT more safely and effectively.
    Materialart: Online-Ressource
    ISSN: 0094-2405 , 2473-4209
    URL: Issue
    Sprache: Englisch
    Verlag: Wiley
    Publikationsdatum: 2023
    ZDB Id: 1466421-5
    Standort Signatur Einschränkungen Verfügbarkeit
    BibTip Andere fanden auch interessant ...
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