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      Skin dose during radiotherapy: a summary and general estimation technique

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          Abstract

          The skin dose associated with radiotherapy may be of interest for clinical evaluation or investigating the risk of late effects. However, skin dose is not intuitive and is difficult to measure. Our objectives were to develop and evaluate a general estimation technique for skin dose based on treatment parameters. The literature on skin dose was supplemented with measurements and Monte Carlo simulations. Using all available data, a general dosimetry system was developed (in the form of a series of equations) to estimate skin dose based on treatment parameters including field size, the presence of a block tray, and obliquity of the treatment field. For out‐of‐field locations, the distance from the field edge was also considered. This dosimetry system was then compared to TLD measurements made on the surface of a phantom. As compared to measurements, the general dosimetry system was able to predict skin dose within, on average, 21% of the local dose (4% of the D max dose). Skin dose for patients receiving radiotherapy can be estimated with reasonable accuracy using a set of general rules and equations.

          PACS numbers: 87.53.‐j, 87.53.Bn, 87.55.ne

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          Most cited references53

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          Dose reconstruction for therapeutic and diagnostic radiation exposures: use in epidemiological studies.

          This paper describes methods developed specifically for reconstructing individual organ- and tissue-absorbed dose of radiation from past exposures from medical treatments and procedures for use in epidemiological studies. These methods have evolved over the past three decades and have been applied to a variety of medical exposures including external-beam radiation therapy and brachytherapy for malignant and benign diseases as well as diagnostic examinations. The methods used for estimating absorbed dose to organs in and outside the defined treatment volume generally require archival data collection, abstraction and review, and phantom measurements to simulate past exposure conditions. Three techniques are used to estimate doses from radiation therapy: (1) calculation in three-dimensional mathematical computer models using an extensive database of out-of-beam doses measured in tissue-equivalent materials, (2) measurement in anthropomorphic phantoms constructed of tissue-equivalent material, and (3) calculation using a three-dimensional treatment-planning computer. For diagnostic exposures, doses are estimated from published data and software based on Monte Carlo techniques. We describe and compare these methods of dose estimation and discuss uncertainties in estimated organ doses and potential for future improvement. Seven epidemiological studies are discussed to illustrate the methods.
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            Accurate skin dose measurements using radiochromic film in clinical applications.

            Megavoltage x-ray beams exhibit the well-known phenomena of dose buildup within the first few millimeters of the incident phantom surface, or the skin. Results of the surface dose measurements, however, depend vastly on the measurement technique employed. Our goal in this study was to determine a correction procedure in order to obtain an accurate skin dose estimate at the clinically relevant depth based on radiochromic film measurements. To illustrate this correction, we have used as a reference point a depth of 70 micron. We used the new GAFCHROMIC dosimetry films (HS, XR-T, and EBT) that have effective points of measurement at depths slightly larger than 70 micron. In addition to films, we also used an Attix parallel-plate chamber and a home-built extrapolation chamber to cover tissue-equivalent depths in the range from 4 micron to 1 mm of water-equivalent depth. Our measurements suggest that within the first millimeter of the skin region, the PDD for a 6 MV photon beam and field size of 10 x 10 cm2 increases from 14% to 43%. For the three GAFCHROMIC dosimetry film models, the 6 MV beam entrance skin dose measurement corrections due to their effective point of measurement are as follows: 15% for the EBT, 15% for the HS, and 16% for the XR-T model GAFCHROMIC films. The correction factors for the exit skin dose due to the build-down region are negligible. There is a small field size dependence for the entrance skin dose correction factor when using the EBT GAFCHROMIC film model. Finally, a procedure that uses EBT model GAFCHROMIC film for an accurate measurement of the skin dose in a parallel-opposed pair 6 MV photon beam arrangement is described.
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              Acute skin toxicity following stereotactic body radiation therapy for stage I non-small-cell lung cancer: who's at risk?

              We examined the rate of acute skin toxicity within a prospectively managed database of patients treated for early-stage non-small-cell lung cancer (NSCLC) and investigated factors that might predict skin toxicity. From May 2006 through January 2008, 50 patients with Stage I NSCLC were treated at Memorial Sloan-Kettering Cancer Center with 60 Gy in three fractions or 44-48 Gy in four fractions. Patients were treated with multiple coplanar beams (3-7, median 4) with a 6 MV linac using intensity-modulated radiotherapy (IMRT) and dynamic multileaf collimation. Toxicity grading was performed and based on the National Cancer Institute Common Terminology Criteria for Adverse Effects. Factors associated with Grade 2 or higher acute skin reactions were calculated by Fisher's exact test. After a minimum 3 months of follow-up, 19 patients (38%) developed Grade 1, 4 patients (8%) Grade 2, 2 patients (4%) Grade 3, and 1 patient Grade 4 acute skin toxicity. Factors associated with Grade 2 or higher acute skin toxicity included using only 3 beams (p = 0.0007), distance from the tumor to the posterior chest wall skin of less than 5 cm (p = 0.006), and a maximum skin dose of 50% or higher of the prescribed dose (p = 0.02). SBRT can be associated with significant skin toxicity. One must consider the skin dose when evaluating the treatment plan and consider the bolus effect of immobilization devices.
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                Author and article information

                Contributors
                sfkry@mdanderson.org
                Journal
                J Appl Clin Med Phys
                J Appl Clin Med Phys
                10.1002/(ISSN)1526-9914
                ACM2
                Journal of Applied Clinical Medical Physics
                John Wiley and Sons Inc. (Hoboken )
                1526-9914
                10 May 2012
                May 2012
                : 13
                : 3 ( doiID: 10.1002/acm2.2012.13.issue-3 )
                : 20-34
                Affiliations
                [ 1 ] Department of Radiation Physics The University of Texas M. D. Anderson Cancer Center Houston TX USA
                Author notes
                [*] [* ]Corresponding author: Stephen F. Kry, Department of Radiation Physics, The University of Texas M. D. Anderson Cancer Center, 1515 Holcombe Boulevard, Houston, TX 77030, USA; phone: (713) 745‐8939; email: sfkry@ 123456mdanderson.org
                Article
                ACM20020
                10.1120/jacmp.v13i3.3734
                5716567
                22584171
                f6991040-664b-462e-8d82-33dbd7e92d05
                © 2012 The Authors.

                This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

                History
                : 09 August 2011
                : 28 December 2011
                Page count
                Figures: 6, Tables: 4, References: 58, Pages: 15, Words: 7159
                Funding
                Funded by: Lance Armstrong Foundation
                Award ID: 6‐39403‐GI
                Funded by: National Cancer Institute
                Award ID: U24CA057227
                Categories
                Radiation Oncology Physics
                Radiation Oncology Physics
                Custom metadata
                2.0
                acm20020
                May 2012
                Converter:WILEY_ML3GV2_TO_NLMPMC version:5.2.5 mode:remove_FC converted:16.11.2017

                skin dose,basal cell carcinoma,radiotherapy,surface dose,skin cancer

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