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      Dosimetric effects of the acuros XB and anisotropic analytical algorithm on volumetric modulated arc therapy planning for prostate cancer using an endorectal balloon

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          Abstract

          Background

          To compare the dosimetric effects of Acuros XB (AXB) and Anisotropic Analytical Algorithm (AAA) on volumetric modulated arc therapy (VMAT) planning for postoperative prostate cancer patients irradiated using an endorectal balloon (ERB).

          Methods

          We measured central axis doses with film in a phantom containing an air cavity, and compared measurements with calculations of the AAA and AXB. For clinical study, 10 patients who had undergone whole pelvic radiotherapy (WPRT) followed by prostatic bed-only radiotherapy (PBRT) using VMAT were enrolled. An ERB was used for PBRT but not for WPRT. To compare dosimetric parameters, the cumulative dose-volume histograms, mean, maximum, and minimum doses were measured for the planning target volume. Homogeneity of plans were confirmed using V 95%, V 107% (V X%, percentage volumes receiving at least X% of prescribed doses) and conformity indices (homogeneity index [HI], conformity index [CI], and conformation number [CN]). We compared volumes of the organ-at-risk receiving 10% to 100% (10-tier at 10% interval) of prescribed doses (V 10% – V 100%).

          Results

          In the phantom study, the AAA showed larger disagreement with the measurements, and overestimated the dose in the air cavity, comparing with the AXB. For WPRT planning, the AAA predicted a lower maximum dose and V 107% than the AXB. For PBRT planning, the AAA estimated a higher minimum dose, lower maximum dose, and smaller V 107%, and larger V 95% than the AXB. Regarding the conformity indices, the AAA was estimated to be more homogenous than the AXB for PBRT planning (HI, 0.088 vs. 0.120, p = 0.005; CI, 1.052 vs. 1.038, p = 0.022; and CN, 0.920 vs. 0.900, p = 0.007) but not for WPRT planning. Among V 10% to V 100% of the rectum, the PBRT exhibited significant discrepancies in V 30%, V 40%, V 70%, V 80%, and V 90%; while the WPRT did in V 20% and V 30%.

          Conclusions

          The phantom study demonstrated that the AXB calculates more accurately in the air cavity than the AAA. In the clinical setting, the AXB exhibited different dosimetric distributions in the VMAT plans for PBRT containing an ERB. The AXB should be considered for prostate cancer patients irradiated with an ERB for better applying of heterogeneous condition.

          Electronic supplementary material

          The online version of this article (doi:10.1186/s13014-015-0346-3) contains supplementary material, which is available to authorized users.

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          Most cited references 31

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          AAPM's TG-51 protocol for clinical reference dosimetry of high-energy photon and electron beams.

          A protocol is prescribed for clinical reference dosimetry of external beam radiation therapy using photon beams with nominal energies between 60Co and 50 MV and electron beams with nominal energies between 4 and 50 MeV. The protocol was written by Task Group 51 (TG-51) of the Radiation Therapy Committee of the American Association of Physicists in Medicine (AAPM) and has been formally approved by the AAPM for clinical use. The protocol uses ion chambers with absorbed-dose-to-water calibration factors, N(60Co)D,w which are traceable to national primary standards, and the equation D(Q)w = MkQN(60Co)D,w where Q is the beam quality of the clinical beam, D(Q)w is the absorbed dose to water at the point of measurement of the ion chamber placed under reference conditions, M is the fully corrected ion chamber reading, and kQ is the quality conversion factor which converts the calibration factor for a 60Co beam to that for a beam of quality Q. Values of kQ are presented as a function of Q for many ion chambers. The value of M is given by M = PionP(TP)PelecPpolMraw, where Mraw is the raw, uncorrected ion chamber reading and Pion corrects for ion recombination, P(TP) for temperature and pressure variations, Pelec for inaccuracy of the electrometer if calibrated separately, and Ppol for chamber polarity effects. Beam quality, Q, is specified (i) for photon beams, by %dd(10)x, the photon component of the percentage depth dose at 10 cm depth for a field size of 10x10 cm2 on the surface of a phantom at an SSD of 100 cm and (ii) for electron beams, by R50, the depth at which the absorbed-dose falls to 50% of the maximum dose in a beam with field size > or =10x10 cm2 on the surface of the phantom (> or =20x20 cm2 for R50>8.5 cm) at an SSD of 100 cm. R50 is determined directly from the measured value of I50, the depth at which the ionization falls to 50% of its maximum value. All clinical reference dosimetry is performed in a water phantom. The reference depth for calibration purposes is 10 cm for photon beams and 0.6R50-0.1 cm for electron beams. For photon beams clinical reference dosimetry is performed in either an SSD or SAD setup with a 10x10 cm2 field size defined on the phantom surface for an SSD setup or at the depth of the detector for an SAD setup. For electron beams clinical reference dosimetry is performed with a field size of > or =10x10 cm2 (> or =20x20 cm2 for R50>8.5 cm) at an SSD between 90 and 110 cm. This protocol represents a major simplification compared to the AAPM's TG-21 protocol in the sense that large tables of stopping-power ratios and mass-energy absorption coefficients are not needed and the user does not need to calculate any theoretical dosimetry factors. Worksheets for various situations are presented along with a list of equipment required.
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            A conformation number to quantify the degree of conformality in brachytherapy and external beam irradiation: application to the prostate.

            This article presents a method of quantitative assessment of the degree of conformality and its designation by a single numerical value. A conformation number is introduced to evaluate objectively the degree of conformality. A comparison is made between the conformation number as found for external beam treatment plans and ultrasonically guided 125I seed implants for localized prostate cancer. The conformation number in case of a planning target volume irradiated with two opposed open beams, three open beams, and three beams with customized blocks amounted to 0.17, 0.39, and 0.65, respectively. The conformation number as found for ultrasonically guided permanent prostate implants using 125I seeds averaged 0.72. The conformation number is a convenient instrument for indicating the degree of conformality by a single numerical value. Treatments with a conformation number greater than 0.60 might be termed conformal radiotherapy.
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              • Article: not found

              Volumetric modulated arc therapy for delivery of prostate radiotherapy: comparison with intensity-modulated radiotherapy and three-dimensional conformal radiotherapy.

              Volumetric modulated arc therapy (VMAT) is a novel form of intensity-modulated radiotherapy (IMRT) optimization that allows the radiation dose to be delivered in a single gantry rotation of up to 360 degrees , using either a constant dose rate (cdr-VMAT) or variable dose rate (vdr-VMAT) during rotation. The goal of this study was to compare VMAT prostate RT plans with three-dimensional conformal RT (3D-CRT) and IMRT plans. The 3D-CRT, five-field IMRT, cdr-VMAT, and vdr-VMAT RT plans were created for 10 computed tomography data sets from patients undergoing RT for prostate cancer. The parameters evaluated included the doses to organs at risk, equivalent uniform doses, dose homogeneity and conformality, and monitor units required for delivery of a 2-Gy fraction. The IMRT and both VMAT techniques resulted in lower doses to normal critical structures than 3D-CRT plans for nearly all dosimetric endpoints analyzed. The lowest doses to organs at risk and most favorable equivalent uniform doses were achieved with vdr-VMAT, which was significantly better than IMRT for the rectal and femoral head dosimetric endpoints (p < 0.05) and significantly better than cdr-VMAT for most bladder and rectal endpoints (p < 0.05). The vdr-VMAT and cdr-VMAT plans required fewer monitor units than did the IMRT plans (relative reduction of 42% and 38%, respectively; p = 0.005) but more than for the 3D-CRT plans (p = 0.005). The IMRT and VMAT techniques achieved highly conformal treatment plans. The vdr-VMAT technique resulted in more favorable dose distributions than the IMRT or cdr-VMAT techniques, and reduced the monitor units required compared with IMRT.
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                Author and article information

                Contributors
                kootaeryool@gmail.com
                jbchung1213@gmail.com
                978sarang@hanmail.net
                sjy515@hanmail.net
                inah228@snu.ac.kr
                jaeskim@snu.ac.kr
                Journal
                Radiat Oncol
                Radiat Oncol
                Radiation Oncology (London, England)
                BioMed Central (London )
                1748-717X
                22 February 2015
                22 February 2015
                2015
                : 10
                Affiliations
                [ ]Department of Radiation Oncology, Seoul National University College of Medicine, 103 Daehak-ro, Jongno-gu, Seoul, 110-799 Korea
                [ ]Department of Radiation Oncology, Seoul National University Bundang Hospital, 82 Gumi-ro, 173beon-gil, Bundang-gu, Seongnam-si, 463-707 Korea
                Article
                346
                10.1186/s13014-015-0346-3
                4342085
                © Koo et al.; licensee BioMed Central. 2015

                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 use, distribution, and reproduction in any medium, provided the original work is properly credited. The Creative Commons Public Domain Dedication waiver ( http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.

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