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      Lung tumor motion reproducibility for five patients who received four-fraction VMAT stereotactic ablative body radiotherapy under constrained breathing conditions: a preliminary study

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          Abstract

          Dear Editor, Several different approaches have been applied to stereotactic hypofractionated radiotherapy for lung tumors, including free breathing, breath-hold, gating, and tracking. Negoro et al. reported that abdominal compression reduced the movement of lung tumors (thereby possibly reducing treatment uncertainty), with portal fluoroscopy being used to measure the tumor movement [1]. Heinzerling et al. [2] and Han et al. [3] confirmed the validity of abdominal compression using 4D computed tomography (CT). Bouilhol et al. also reconfirmed the validity of abdominal compression using 4D CT and reported that the internal target volume was significantly reduced for lower lobe tumors [4]. On the other hand, Bissonnette et al. reported that abdominal compression increased the variation of tumor motion by referring to their 4D cone-beam CT (CBCT) data, contending that longer treatment time to include the abdominal compression procedure may reduce the reproducibility of tumor motion [5]. Richmond et al. [6] and Mampuya et al. [7] also reported significant variation in the average tumor position under abdominal compression from their 3D CBCT data. Using a 4D planning CT imager, Aquilion LB, (Toshiba, Ohtawara, Japan) we calculated 3D lung tumor motion trajectories with an Anzai belt (Anzai, Tokyo, Japan) and stereotactic body frame with an abdominal compression plate (Elekta AB, Stockholm, Sweden) for five patients who received four-fraction VMAT stereotactic ablative body radiotherapy (SABR). In addition, the motion trajectories of lung tumors were calculated using 4D CBCT imaging functionality provided by an X-ray Volume Imaging (XVI) system version 4.5 (Elekta AB, Stockholm, Sweden) both immediately before and during treatment. The pre-treatment 4D CBCT data were acquired by the built-in XVI software, Symmetry, whereas in-treatment 4D CBCT was obtained by in-house software using projection images acquired during VMAT delivery [8]. The breathing amplitudes obtained using the 4D planning CT and 4D CBCT were divided into five equal intervals, i.e. ten breathing phases. Subsequently, the trajectory was obtained by calculating each gravity center of the tumor for each phase. The resulting trajectory was visually inspected to analyze the reproducibility of the tumor motion at the time of planning, immediately before treatment and during treatment. The data acquisition times for pre-treatment and in-treatment CBCT are typically 4 min and 3.5 min, respectively. Therefore, the calculated trajectories are time-averaged during these periods. As reported previously, a large variation in the average tumor position was observed between planning and pre-treatment CBCT imaging. However, this offset would be automatically corrected by the XVI software, Symmetry, after automatic bone matching, so that the patient couch would be repositioned according to a time-averaged tumor position on each treatment day. Having this clinical workflow in mind, tumor motion reproducibility was analyzed after subtracting the average 3D position from each trajectory. Figure 1a–e shows the lung tumor trajectories during the planning times (in gray) and pre-treatment times in the four fractions (in red, green, blue and violet) for the five patients. Throughout this letter, the x, y and z axes correspond to the lateral, anteroposterior and craniocaudal directions, respectively. A large interpatient variability was observed: Fig. 1a shows nearly one-dimensional movement in the craniocaudal direction. Figure 1c–e shows much smaller but more isotropic tumor movements with significant hysteresis. This may be due to variation in the tumor locations, the abdominal compression forces, and the compressed positions between patients. In addition, if we consider a typical lung tumor having a dimension of 10 mm or larger, the trajectory differences between the planning and pre-treatment times for each patient may be clinically ignored. Figure 1a–e also suggests that 4D CBCT may be used for calculating the internal target volume (ITV) and the planning target volume (PTV). Fig. 1. 3D lung tumor trajectories during the planning time (in gray) and pre-treatment times in the four fractions (in red, green, blue and violet) for the five patients. The x, y and z axes correspond to the lateral, anteroposterior and craniocaudal directions, respectively. Figure 2a–d compares lung tumor trajectories obtained by pre-treatment 4D CBCT (thin line) with those obtained by in-treatment 4D CBCT (thick line), fraction by fraction, for a patient. Figure 3a–d shows another trajectory comparison for a different patient. Again, if we consider a tumor size of 10 mm or larger, the observed differences between pre-treatment and in-treatment times may be clinically ignored. Fig. 2. 3D lung tumor trajectories obtained by pre-treatment 4D CBCT (thin line) and those obtained by in-treatment 4D CBCT (thick line), fraction by fraction, for a patient. The x, y and z axes correspond to the lateral, anteroposterior and craniocaudal directions, respectively. Fig. 3. 3D lung tumor trajectories obtained by pre-treatment 4D CBCT (thin line) and those obtained by in-treatment 4D CBCT (thick line), fraction by fraction, for a different patient. The x, y and z axes correspond to the lateral, anteroposterior and craniocaudal directions, respectively. In conclusion, we confirmed the reproducibility of lung tumor movement using 4D planning CT and 4D CBCT for five patients who received four-fraction VMAT SABR under constrained breathing conditions. The results appear to be clinically acceptable, but further study is needed because of the small data size of this preliminary study. It is anticipated that the flattening-filter-free technique may increase breathing trajectory reproducibility due to its faster dose delivery [9]. In addition, reproducibility should also be discussed in terms of dose calculation in 4D [10]. The current study is in compliance with the ethical guidelines of the hospital, and written informed consent was obtained before the treatment was initiated.

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          Most cited references 11

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          Quantifying interfraction and intrafraction tumor motion in lung stereotactic body radiotherapy using respiration-correlated cone beam computed tomography.

          Stereotactic body radiation therapy (SBRT) is an effective treatment for medically inoperable Stage I non-small-cell lung cancer. However, changes in the patient's breathing patterns during the course of SBRT may result in a geographic miss or an overexposure of healthy tissues to radiation. However, the precise extent of these changes in breathing pattern is not well known. We evaluated the inter- and intrafractional changes in tumor motion amplitude (DeltaM) over an SBRT course. Eighteen patients received image-guided SBRT delivered in three fractions; this therapy was done with abdominal compression in four patients. For each fraction, cone beam computed tomography (CBCT) was performed for tumor localization (+/- 3-mm tolerance) and then repeated to confirm geometric accuracy. Additional CBCT images were acquired at the midpoint and end of each SBRT fraction. Respiration-correlated CBCT (rcCBCT) reconstructions allowed retrospective assessment of inter- and intrafractional DeltaM by a comparison of tumor displacements in all four-dimensional CT and rcCBCT scans. The DeltaM was measured in mediolateral, superior-inferior, and anterior-posterior directions. A total of 201 rcCBCT images were analyzed. The mean time from localization of the tumor to the end-fraction CBCT was 35 +/- 7 min. Compared with the motion recorded on four-dimensional CT, the mean DeltaM was 0.4, 1.0, and 0.4 mm, respectively, in the mediolateral, superior-inferior, and anterior-posterior directions. On treatment, the observed DeltaM was, on average, <1 mm; no DeltaM was statistically different with respect to the initial rcCBCT. However, patients in whom abdominal compression was used showed a statistically significant difference (p < 0.05) in the variance of DeltaM with respect to the initial rcCBCT in the superior-inferior direction. The inter- and intrafractional DeltaM that occur during a course of lung SBRT are small. However, abdominal compression causes larger variations in the time spent on the treatment couch and in the inter- and intrafractional DeltaM values.
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            Four-dimensional computed tomography scan analysis of tumor and organ motion at varying levels of abdominal compression during stereotactic treatment of lung and liver.

            To investigate the effectiveness of different abdominal compression levels on tumor and organ motion during stereotactic body radiotherapy of lower lobe lung and liver tumors using four-dimensional (4D)-CT scan analysis. Three 4D-CT scans were acquired for 10 patients first using with no compression and then compared with two different levels of abdominal compression. The position of the tumor and various organs were defined at the peak inspiratory and expiratory phases and compared to determine the maximum motion. Mean (+/-SD) medium compression force (MC) and high compression force (HC) were 47.6 +/- 16.0 N and 90.7 +/- 27.1 N, respectively. Mean overall tumor motion was 13.6 mm (2sigma [2 sigma] 11.5-15.6), 8.3 mm (2sigma 6.0-10.5), and 7.2 mm (2sigma 5.4-9.0) for no compression, MC, and HC, respectively. A significant difference in the control of both superior-inferior (SI) and overall motion of tumors was seen with the application of MC and HC when compared with no compression (p < 0.0001 for both). High compression force improved SI and overall tumor motion compared with MC, but this was only significant for SI motion (p = 0.04 and p = 0.06). Significant control of organ motion was only seen in the pancreas (p = 0.01). Four-dimensional CT shows significant control of both lower lobe lung and liver tumors using abdominal compression. High levels of compression improve SI tumor motion when compared with MC.
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              The effectiveness of an immobilization device in conformal radiotherapy for lung tumor: reduction of respiratory tumor movement and evaluation of the daily setup accuracy.

              To evaluate the daily setup accuracy and the reduction of respiratory tumor movement using a body frame in conformal therapy for solitary lung tumor. Eighteen patients with a solitary lung tumor underwent conformal therapy using a body frame. The body shell of the frame was shaped to the patient's body contour. The respiratory tumor movement was estimated using fluoroscopy, and if it was greater than 5 mm, pressure was applied to the patient's abdomen with the goal of minimizing tumor movement. CT images were then obtained, and a treatment planning was made. A total dose of 40 or 48 Gy was delivered in 4 fractions. Portal films were obtained at each treatment, and the field displacements between them and the simulation films were measured for daily setup errors. The patients were repositioned if the setup error was greater than 3 mm. Correlations were analyzed between patient characteristics and the tumor movement, or the tumor movement reduction and the daily setup errors. Respiratory tumor movement ranged from 0 to 20 mm (mean 7.7 mm). The abdominal press reduced the tumor movement significantly from a range of 8 to 20 mm to a range of 2 to 11 mm (p = 0.0002). Daily setup errors were within 5 mm in 90%, 100%, and 93% of all verifications in left-right, anterior-posterior, and cranio-caudal directions, respectively. Patient repositioning was performed in 25% of all treatments. No significant correlation was detected between patient characteristics and tumor movement, tumor movement reduction, and the daily setup errors. The abdominal press was successful in reducing the respiratory tumor movement. Daily setup accuracy using the body frame was acceptable. Verification should be performed at each treatment in hypofractionated conformal therapy.
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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
                November 2014
                25 June 2014
                25 June 2014
                : 55
                : 6
                : 1199-1201
                Affiliations
                [1 ]University of Tokyo Hospital , Department of Radiology, Hongo, Bunkyo-ku, Tokyo, Japan
                [2 ]Elekta KK, Research Physics , Shibaura, Minato-ku, Tokyo, Japan
                Author notes
                [* ]Corresponding author. k-nak@ 123456fg7.so-net.ne.jp
                Article
                rru055
                10.1093/jrr/rru055
                4229920
                24966399
                © The Author 2014. Published by Oxford University Press on behalf of The Japan Radiation Research Society and Japanese Society for Radiation Oncology.

                This is an Open Access article distributed under the terms of the Creative Commons Attribution License ( http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited.

                Product
                Categories
                Letter to the Editor

                Oncology & Radiotherapy

                sabr, vmat, tumor motion reproducibility

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