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      The dosimetric impact of respiratory breast movement and daily setup error on tangential whole breast irradiation using conventional wedge, field-in-field and irregular surface compensator techniques

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          Abstract

          To evaluate the dosimetric impact of respiratory breast motion and daily setup error on whole breast irradiation (WBI) using three irradiation techniques; conventional wedge (CW), field-in-field (FIF) and irregular surface compensator (ISC). WBI was planned for 16 breast cancer patients. The dose indices for evaluated clinical target volume (CTV evl), lung, and body were evaluated. For the anterior-posterior (AP) respiratory motion and setup error of a single fraction, the isocenter was moved according to a sine function, and the dose indices were averaged over one period. Furthermore, the dose indices were weighted according to setup error frequencies that have a normal distribution to model systematic and random setup error for the entire treatment course. In all irradiation techniques, AP movement has a significant impact on dose distribution. CTV evlD 95 (the minimum relative dose that covers 95 % volume) and V 95 (the relative volume receiving 95 % of the prescribed dose) were observed to significantly decrease from the original ISC plan when simulated for the entire treatment course. In contrast, the D 95, V 95 and dose homogeneity index did not significantly differ from those of the original plans for FIF and CW. With regard to lung dose, the effect of motion was very similar among all three techniques. The dosimetric impact of AP respiratory breast motion and setup error was largest for the ISC technique, and the second greatest effect was observed with the FIF technique. However, these variations are relatively small.

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          Errors and margins in radiotherapy.

          Clinical radiotherapy procedures aim at high accuracy. However, there are many error sources that act during treatment preparation and execution that limit the accuracy. As a consequence, a safety margin is required to ensure that the planned dose is actually delivered to the target for (almost) all patients. Before treatment planning, a planning computed tomography scan is made. In particular, motion of skin with respect to the internal anatomy limits the reproducibility of this step, introducing a systematic setup error. The second important error source is organ motion. The tumor is imaged in an arbitrary position, leading to a systematic organ motion error. The image may also be distorted because of the interference of the scanning process and organ motion. A further systematic error introduced during treatment planning is caused by the delineation process. During treatment, the most important errors are setup error and organ motion leading to day-to-day variations. There are many ways to define the margins required for these errors. In this article, an overview is given of errors in radiotherapy and margin recipes, based on physical and biological considerations. Respiration motion is treated separately.
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            Optimizing breast cancer treatment efficacy with intensity-modulated radiotherapy.

            To present our clinical experience using intensity-modulated radiation therapy (IMRT) to improve dose uniformity and treatment efficacy in patients with early-stage breast cancer treated with breast-conserving therapy. A total of 281 patients with Stage 0, I, and II breast cancer treated with breast-conserving therapy received whole breast RT after lumpectomy using our static, multileaf collimator (sMLC) IMRT technique. The technical and practical aspects of implementing this technique on a large scale in the clinic were analyzed. The clinical outcome of patients treated with this technique was also reviewed. The median time required for three-dimensional alignment of the tangential fields and dosimetric IMRT planning was 40 and 45 min, respectively. The median number of sMLC segments required per patient to meet the predefined dose-volume constraints was 6 (range 3-12). The median percentage of the treatment given with open fields (no sMLC segments) was 83% (range 38-96%), and the median treatment time was <10 min. The median volume of breast receiving 105% of the prescribed dose was 11% (range 0-67.6%). The median breast volume receiving 110% of the prescribed dose was 0% (range 0-39%), and the median breast volume receiving 115% of the prescribed dose was also 0%. A total of 157 patients (56%) experienced Radiation Therapy Oncology Group Grade 0 or I acute skin toxicity; 102 patients (43%) developed Grade II acute skin toxicity and only 3 (1%) experienced Grade III toxicity. The cosmetic results at 12 months (95 patients analyzable) were rated as excellent/good in 94 patients (99%). No skin telengiectasias, significant fibrosis, or persistent breast pain was noted. The use of intensity modulation with our sMLC technique for tangential whole breast RT is an efficient method for achieving a uniform and standardized dose throughout the whole breast. Strict dose-volume constraints can be readily achieved resulting in both uniform coverage of breast tissue and a potential reduction in acute and chronic toxicities. Because the median number of sMLC segments required per patient is only 6, the treatment time is equivalent to conventional wedged-tangent treatment techniques. As a result, widespread implementation of this technology can be achieved with minimal imposition on clinic resources and time constraints.
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              Intensity-modulated radiotherapy results in significant decrease in clinical toxicities compared with conventional wedge-based breast radiotherapy.

              We have previously demonstrated that intensity-modulated radiotherapy (IMRT) with a static multileaf collimator process results in a more homogenous dose distribution compared with conventional wedge-based whole breast irradiation (WBI). In the present analysis, we reviewed the acute and chronic toxicity of this IMRT approach compared with conventional wedge-based treatment. A total of 172 patients with Stage 0-IIB breast cancer were treated with lumpectomy followed by WBI. All patients underwent treatment planning computed tomography and received WBI (median dose, 45 Gy) followed by a boost to 61 Gy. Of the 172 patients, 93 (54%) were treated with IMRT, and the 79 patients (46%) treated with wedge-based RT in a consecutive fashion immediately before this cohort served as the control group. The median follow-up was 4.7 years. A significant reduction in acute Grade 2 or worse dermatitis, edema, and hyperpigmentation was seen with IMRT compared with wedges. A trend was found toward reduced acute Grade 3 or greater dermatitis (6% vs. 1%, p = 0.09) in favor of IMRT. Chronic Grade 2 or worse breast edema was significantly reduced with IMRT compared with conventional wedges. No difference was found in cosmesis scores between the two groups. In patients with larger breasts (> or =1,600 cm(3), n = 64), IMRT resulted in reduced acute (Grade 2 or greater) breast edema (0% vs. 36%, p <0.001) and hyperpigmentation (3% vs. 41%, p = 0.001) and chronic (Grade 2 or greater) long-term edema (3% vs. 30%, p = 0.007). The use of IMRT in the treatment of the whole breast results in a significant decrease in acute dermatitis, edema, and hyperpigmentation and a reduction in the development of chronic breast edema compared with conventional wedge-based RT.
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                Author and article information

                Journal
                J Radiat Res
                J. Radiat. Res
                jrr
                jrr
                Journal of Radiation Research
                Oxford University Press
                0449-3060
                1349-9157
                January 2013
                1 August 2012
                1 August 2012
                : 54
                : 1
                : 157-165
                Affiliations
                Department of Radiology, Faculty of Medicine, Juntendo University, 2-1-1 Hongo, Bunkyo-ku, Tokyo 113-8421, Japan
                Author notes
                [* ]Corresponding author. Tel: +81-3-3813-3111; Fax: +81-3-6801-5736; Email: tfuruya@ 123456juntendo.ac.jp
                Article
                rrs064
                10.1093/jrr/rrs064
                3534267
                22859565
                cb5cd021-509d-476b-9078-e915d0acd03b
                © The Author 2012. Published by Oxford University Press on behalf of The Japan Radiation Research Society and Japanese Society for Therapeutic Radiology and Oncology.

                This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License ( http://creativecommons.org/licenses/by-nc/3.0/), which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

                History
                : 30 November 2011
                : 5 July 2012
                : 6 July 2012
                Categories
                Technology

                Oncology & Radiotherapy
                respiratory motion,setup error,field-in-field,electronic compensator,whole breast irradiation

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