Browsing by Subject "Radiotherapy, Conformal"

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    Clinical assessment and characterization of a dual tube kilovoltage X-ray localization system in the radiotherapy treatment room.
    (Journal of applied clinical medical physics, 2008-01-13) Lee, Sung-Woo; Jin, Jian-Yue; Guan, Huaiqun; Martin, Flavious; Kim, Jae Ho; Yin, Fang-Fang
    INTRODUCTION:Although flat-panel based X-ray imaging has been well tested in diagnostic radiology, its use as an image-guided-radiotherapy (IGRT) system in a treatment room is new and requires systematic assessment. MATERIALS AND METHODS:BrainLab Novalis IGRT system was used for this study. It consists of two floor mounted kV X-ray tubes projecting obliquely into two flat-panel detectors mounted on the ceiling. The system automatically fuses the 2D localization images with 3D simulation CT image to provide positioning guidance. The following characteristics of the system were studied: (1) Coincidence of the isocenters between the IGRT and Linac; (2) Image quality; (3) Exposure; (4) Linearity, uniformity and repeatability. RESULTS:(1) Localization accuracy and coincidence of the isocenters between the IGRT and Linac was better than 1-mm. (2) The spatial resolution was quantified using the relative modulation-transfer-function with f50=0.7-0.9 lp/mm. The variation of contrast-noise-ratio with technical settings was measured. (3) The maximal exposure of an image was less than 95 mR. An empirical relation between the exposure and the X-ray technical setting was derived. (4) The linearity, uniformity and repeatability of the system generally meet the requirements. CONCLUSION:The system can be safely and reliably used as a target localization device.
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    Flattening filter-free accelerators: a report from the AAPM Therapy Emerging Technology Assessment Work Group.
    (Journal of applied clinical medical physics, 2015-05-08) Xiao, Ying; Kry, Stephen F; Popple, Richard; Yorke, Ellen; Papanikolaou, Niko; Stathakis, Sotirios; Xia, Ping; Huq, Saiful; Bayouth, John; Galvin, James; Yin, Fang-Fang
    This report describes the current state of flattening filter-free (FFF) radiotherapy beams implemented on conventional linear accelerators, and is aimed primarily at practicing medical physicists. The Therapy Emerging Technology Assessment Work Group of the American Association of Physicists in Medicine (AAPM) formed a writing group to assess FFF technology. The published literature on FFF technology was reviewed, along with technical specifications provided by vendors. Based on this information, supplemented by the clinical experience of the group members, consensus guidelines and recommendations for implementation of FFF technology were developed. Areas in need of further investigation were identified. Removing the flattening filter increases beam intensity, especially near the central axis. Increased intensity reduces treatment time, especially for high-dose stereotactic radiotherapy/radiosurgery (SRT/SRS). Furthermore, removing the flattening filter reduces out-of-field dose and improves beam modeling accuracy. FFF beams are advantageous for small field (e.g., SRS) treatments and are appropriate for intensity-modulated radiotherapy (IMRT). For conventional 3D radiotherapy of large targets, FFF beams may be disadvantageous compared to flattened beams because of the heterogeneity of FFF beam across the target (unless modulation is employed). For any application, the nonflat beam characteristics and substantially higher dose rates require consideration during the commissioning and quality assurance processes relative to flattened beams, and the appropriate clinical use of the technology needs to be identified. Consideration also needs to be given to these unique characteristics when undertaking facility planning. Several areas still warrant further research and development. Recommendations pertinent to FFF technology, including acceptance testing, commissioning, quality assurance, radiation safety, and facility planning, are presented. Examples of clinical applications are provided. Several of the areas in which future research and development are needed are also indicated.
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    ItemOpen Access
    Knowledge-based IMRT treatment planning for prostate cancer.
    (2011) Chanyavanich, Vorakarn
    The goal of intensity-modulated radiation therapy (IMRT) treatment plan optimization is to produce a cumulative dose distribution that satisfies both the dose prescription and the normal tissue dose constraints. The typical manual treatment planning process is iterative, time consuming, and highly dependent on the skill and experience of the planner. We have addressed this problem by developing a knowledge based approach that utilizes a database of prior plans to leverage the planning expertise of physicians and physicists at our institution. We developed a case-similarity algorithm that uses mutual information to identify a similar matched case for a given query case, and various treatment parameters from the matched case are then adapted to derive new treatment plans that are patient specific. We used 10 randomly selected cases matched against a knowledge base of 100 cases to demonstrate that new, clinically acceptable IMRT treatment plans can be developed. This approach substantially reduced planning time by skipping all but the last few iterations of the optimization process. Additionally, we established a simple metric based on the areas under the curve (AUC) of the dose volume histogram (DVH), specifically for the planning target volume (PTV), rectum, and bladder. This plan quality metric was used to successfully rank order the plan quality of a collection of knowledgebased plans. Further, we used 100 pre-optimized plans (20 query x 5 matches) to show that the average normalized MI score can be used as a surrogate of overall plan quality. Plans of lower pre-optimized plan quality tended to improve substantially after optimization, though its final plan quality did not improve to the same level as a plan that has a higher pre-optimized plan quality to begin with. Optimization usually improved PTV coverage slightly while providing substantial dose sparing for both bladder and rectum of 12.4% and 9.1% respectively. Lastly, we developed new treatment plans for cases selected from an outside institution matched against our sitespecific database. The knowledge-based plans are very comparable to the original manual plan, providing adequate PTV coverage as well as substantial improvement in dose sparing to the rectum and bladder. In conclusion, we found that a site-specific database of prior plans can be effectively used to design new treatment plans for our own institution as well as outside cases. Specifically, knowledge-based plans can provide clinically acceptable planning target volume coverage and clinically acceptable dose sparing to the rectum and bladder. This approach has been demonstrated to improve the efficiency of the treatment planning process, and may potentially improve the quality of patient care by enabling more consistent treatment planning across institutions.