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      Random variation in rectal position during radiotherapy for prostate cancer is two to three times greater than that predicted from prostate motion

      research-article
      , MSc, FRCR 1 , , , MSc 2 , , PhD 3 , , MA (Oxon), PhD 2 , , PhD, MIMechE 4 , , PhD 5 , , PhD, FIPEM 3 , , MRCP, FRCR 6 , , MD, FRCR 1 , , MSc 1 , , MD, FRCR 1
      The British Journal of Radiology
      The British Institute of Radiology.

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          Abstract

          Objective:

          Radiotherapy for prostate cancer does not explicitly take into account daily variation in the position of the rectum. It is important to accurately assess accumulated dose ( D A) to the rectum in order to understand the relationship between dose and toxicity. The primary objective of this work was to quantify systematic ( Σ) and random ( σ) variation in the position of the rectum during a course of prostate radiotherapy.

          Methods:

          The rectum was manually outlined on the kilo-voltage planning scan and 37 daily mega-voltage image guidance scans for 10 participants recruited to the VoxTox study. The femoral heads were used to produce a fixed point to which all rectal contours were referenced.

          Results:

          Σ [standard deviation (SD) of means] between planning and treatment was 4.2 mm in the anteroposterior (AP) direction and 1.3 mm left–right (LR). σ (root mean square of SDs) was 5.2 mm AP and 2.7 mm LR. Superior–inferior variation was less than one slice above and below the planning position.

          Conclusion:

          Our results for Σ are in line with published data for prostate motion. σ, however, was approximately twice as great as that seen for prostate motion. This suggests that D A may differ from planned dose in some patients treated with radiotherapy for prostate cancer.

          Advances in knowledge:

          This work is the first to use daily imaging to quantify Σ and σ of the rectum in prostate cancer. σ was found to be greater than published data, providing strong rationale for further investigation of individual D A.

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          Most cited references43

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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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            Quantitative Analyses of Normal Tissue Effects in the Clinic (QUANTEC): an introduction to the scientific issues.

            Advances in dose-volume/outcome (or normal tissue complication probability, NTCP) modeling since the seminal Emami paper from 1991 are reviewed. There has been some progress with an increasing number of studies on large patient samples with three-dimensional dosimetry. Nevertheless, NTCP models are not ideal. Issues related to the grading of side effects, selection of appropriate statistical methods, testing of internal and external model validity, and quantification of predictive power and statistical uncertainty, all limit the usefulness of much of the published literature. Synthesis (meta-analysis) of data from multiple studies is often impossible because of suboptimal primary analysis, insufficient reporting and variations in the models and predictors analyzed. Clinical limitations to the current knowledge base include the need for more data on the effect of patient-related cofactors, interactions between dose distribution and cytotoxic or molecular targeted agents, and the effect of dose fractions and overall treatment time in relation to nonuniform dose distributions. Research priorities for the next 5-10 years are proposed. Copyright 2010 Elsevier Inc. All rights reserved.
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              Normal tissue reactions to radiotherapy: towards tailoring treatment dose by genotype.

              A key challenge in radiotherapy is to maximize radiation doses to cancer cells while minimizing damage to surrounding healthy tissue. As severe toxicity in a minority of patients limits the doses that can be safely given to the majority, there is interest in developing a test to measure an individual's radiosensitivity before treatment. Variation in sensitivity to radiation is an inherited genetic trait and recent progress in genotyping raises the possibility of genome-wide studies to characterize genetic profiles that predict patient response to radiotherapy.
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                Author and article information

                Journal
                Br J Radiol
                Br J Radiol
                bjr
                The British Journal of Radiology
                The British Institute of Radiology.
                0007-1285
                1748-880X
                October 2014
                16 September 2014
                16 September 2014
                : 87
                : 1042
                : 20140343
                Affiliations
                [ 1 ]Department of Oncology, Addenbrooke's Hospital, University of Cambridge, Cambridge, UK
                [ 2 ]Department of Physics, University of Cambridge, Cavendish Laboratory, Cambridge, UK
                [ 3 ]Department of Medical Physics, Cambridge University Hospitals NHS Foundation Trust, Cambridge, UK
                [ 4 ]Department of Engineering, University of Cambridge, Cambridge, UK
                [ 5 ]MRC Biostatistics Unit, Institute of Public Health, University of Cambridge, UK
                [ 6 ]Department of Radiology, Cambridge University Hospitals NHS Foundation Trust, Cambridge, UK
                Author notes
                Address correspondence to: Dr Jessica Scaife. E-mail: jessica.scaife@ 123456doctors.net.uk
                Article
                14343
                10.1259/bjr.20140343
                4170867
                25138155
                a6a7627e-7ffa-4951-a6dd-ef5e9c5b8126
                © 2014 The Authors. Published by the British Institute of Radiology

                This is an Open Access article distributed under the terms of the Creative Commons Attribution 3.0 Unported License http://creativecommons.org/licenses/by/3.0/, which permits unrestricted use, distribution and reproduction in any medium, provided the original author and source are credited.

                History
                : Received on May 9, 2014
                : Revised on August 11, 2014
                : Accepted on August 18, 2014
                Page count
                Figures: 8, Tables: 0, References: 48, Pages: 12
                Categories
                Full Paper
                Radiotherapy and Oncology

                Radiology & Imaging
                Radiology & Imaging

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