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      Efficacy of the Dynamic Jaw Mode in Helical Tomotherapy With Static Ports for Breast Cancer

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          Abstract

          The recently developed dynamic jaw technology of tomotherapy can reduce craniocaudal dose spread without much prolonging the treatment time. This study aimed to investigate the efficacy of the dynamic jaw mode for tomotherapy of breast cancer. Static tomotherapy plans of the whole breast and supraclavicular regional lymph nodes, and plans for the whole breast only were generated in 25 patients with left-sided breast cancer. Plans with a field width of 2.5 or 5 cm with the dynamic or fixed jaw modes were made for each patient. The prescribed dose was 50 Gy in 25 fractions. In whole breast and supraclavicular nodal radiotherapy, dose distributions and homogeneity of the planning target volume (PTV) with the dynamic jaw mode were slightly inferior to those with the fixed jaw mode with a 5-cm field width ( P < .05). However, lung low-dose volumes and mean doses of the larynx, thyroid, skin, and all the healthy tissues combined were smaller with the dynamic jaw mode than with the fixed jaw mode with a 5-cm field width ( P < .001). In whole breast radiotherapy, mean doses of the skin and healthy tissues were lower with the dynamic jaw mode than with the fixed jaw mode with a 5-cm field width ( P < .001) without significant differences in PTV dose distributions, homogeneity, and conformity. The dynamic jaw mode provided better sparing of organs at risks with minimal disturbance of dose–volume indices of PTV. Considering the treatment time, the 5-cm-field dynamic jaw mode is more efficient than the 2.5-cm fixed jaw mode.

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          A conformation number to quantify the degree of conformality in brachytherapy and external beam irradiation: application to the prostate.

          This article presents a method of quantitative assessment of the degree of conformality and its designation by a single numerical value. A conformation number is introduced to evaluate objectively the degree of conformality. A comparison is made between the conformation number as found for external beam treatment plans and ultrasonically guided 125I seed implants for localized prostate cancer. The conformation number in case of a planning target volume irradiated with two opposed open beams, three open beams, and three beams with customized blocks amounted to 0.17, 0.39, and 0.65, respectively. The conformation number as found for ultrasonically guided permanent prostate implants using 125I seeds averaged 0.72. The conformation number is a convenient instrument for indicating the degree of conformality by a single numerical value. Treatments with a conformation number greater than 0.60 might be termed conformal radiotherapy.
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            Dosimetric comparison of left-sided whole breast irradiation with 3DCRT, forward-planned IMRT, inverse-planned IMRT, helical tomotherapy, and topotherapy.

            To compare left-sided whole breast conventional and intensity-modulated radiotherapy (IMRT) treatment planning techniques. Treatment plans were created for 10 consecutive patients. Three-dimensional conformal radiotherapy (3DCRT), forward-planned IMRT (for-IMRT), and inverse-planned IMRT (inv-IMRT) used two tangent beams. For-IMRT utilized up to four segments per beam. For helical tomotherapy (HT) plans, beamlet entrance and/or exit to critical structures was blocked. Topotherapy plans, which used static gantry angles with simultaneous couch translation and inverse-planned intensity modulation, used two tangent beams. Plans were normalized to 50Gy to 95% of the retracted PTV. Target max doses were reduced with for-IMRT compared to 3DCRT, which were further reduced with HT, topotherapy, and inv-IMRT. HT resulted in lowest heart and ipsilateral lung max doses, but had higher mean doses. Inv-IMRT and topotherapy reduced ipsilateral lung mean and max doses compared to 3DCRT and for-IMRT. All modalities evaluated provide adequate coverage of the intact breast. HT, topotherapy, and inv-IMRT can reduce high doses to the target and normal tissues, although HT results in increased low doses to large volume of normal tissue. For-IMRT improves target homogeneity compared with 3DCRT, but to a lesser degree than the inverse-planned modalities. Copyright © 2011 Elsevier Ireland Ltd. All rights reserved.
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              Helical tomotherapy planning for left-sided breast cancer patients with positive lymph nodes: comparison to conventional multiport breast technique.

              To evaluate the feasibility of using helical tomotherapy for locally advanced left-sided breast cancer. Treatment plans were generated for 10 left-sided breast cancer patients with positive lymph nodes comparing a multiport breast (three-dimensional) technique with the tomotherapy treatment planning system. The planning target volumes, including the chest wall/breast, supraclavicular, axillary, and internal mammary lymph nodes, were contoured. The treatment plans were generated on the tomotherapy treatment planning system to deliver 50.4 Gy to the planning target volume. To spare the contralateral tissues, directional blocking was applied to the right breast and right lung. The optimization goals were to protect the lungs, heart, and right breast. The tomotherapy plans increased the minimal dose to the planning target volume (minimal dose received by 99% of target volume = 46.2 +/- 1.3 Gy vs. 27.9 +/- 17.1 Gy) while improving the dose homogeneity (dose difference between the minimal dose received by 5% and 95% of the planning target volume = 7.5 +/- 1.8 Gy vs. 37.5 +/- 26.9 Gy). The mean percentage of the left lung volume receiving >or=20 Gy in the tomotherapy plans decreased from 32.6% +/- 4.1% to 17.6% +/- 3.5%, while restricting the right-lung mean dose to or=5 Gy for the total lung increased from 25.2% +/- 4.2% for the three-dimensional technique to 46.9% +/- 8.4% for the tomotherapy plan. The mean volume receiving >or=35 Gy for the heart decreased from 5.6% +/- 4.8% to 2.2% +/- 1.5% in the tomotherapy plans. However, the mean heart dose for tomotherapy delivery increased from 7.5 +/- 3.4 Gy to 12.2 +/- 1.8 Gy. The tomotherapy plans provided better dose conformity and homogeneity than did the three-dimensional plans for treatment of left-sided breast tumors with regional lymph node involvement, while allowing greater sparing of the heart and left lung from doses associated with increased complications.
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                Author and article information

                Journal
                Technol Cancer Res Treat
                Technol. Cancer Res. Treat
                TCT
                sptct
                Technology in Cancer Research & Treatment
                SAGE Publications (Sage CA: Los Angeles, CA )
                1533-0346
                1533-0338
                August 2015
                August 2015
                : 14
                : 4
                : 459-465
                Affiliations
                [1 ]Department of Radiology, Nagoya City University Graduate School of Medical Sciences, Nagoya, Japan
                [2 ]Department of Radiology, Okazaki City Hospital, Okazaki, Japan
                [3 ]Department of Radiation Oncology, Nagoya Proton Therapy Center, Nagoya, Japan
                [4 ]Department of Radiology, Narita Memorial Hospital, Toyohashi, Japan
                Author notes
                [*]Chikao Sugie, MD, Department of Radiology, Nagoya City University Graduate School of Medical Sciences, 1 Kawasumi, Mizuho-cho, Mizuho-ku, Nagoya, Japan. Email: chikao@ 123456bg8.so-net.ne.jp
                Article
                10.1177_1533034614558746
                10.1177/1533034614558746
                4535315
                25398681
                324467f1-5db9-45cb-894d-d0b9012e2ecb
                © The Author(s) 2014

                This article is distributed under the terms of the Creative Commons Attribution-NonCommercial 3.0 License ( http://www.creativecommons.org/licenses/by-nc/3.0/) which permits non-commercial use, reproduction and distribution of the work without further permission provided the original work is attributed as specified on the SAGE and Open Access page( http://www.uk.sagepub.com/aboutus/openaccess.htm).

                History
                : 18 July 2014
                : 8 September 2014
                : 6 October 2014
                Categories
                Original Articles
                Radiotherapy

                dynamic jaw mode,static tomotherapy delivery,breast cancer

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