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      Coplanar VMAT vs. noncoplanar VMAT in the treatment of sinonasal cancer

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          Abstract

          Previous studies showed that noncoplanar intensity-modulated radiotherapy (NC-IMRT) for sinonasal cancer is superior to coplanar intensity-modulated radiotherapy (IMRT). Volumetric-modulated arc therapy (VMAT) is a newly introduced treatment modality, and the performance of noncoplanar VMAT for sinonasal cancer has not been well described to date.

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          Most cited references27

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          Volumetric modulated arc therapy: a review of current literature and clinical use in practice.

          Volumetric modulated arc therapy (VMAT) is a novel radiation technique, which can achieve highly conformal dose distributions with improved target volume coverage and sparing of normal tissues compared with conventional radiotherapy techniques. VMAT also has the potential to offer additional advantages, such as reduced treatment delivery time compared with conventional static field intensity modulated radiotherapy (IMRT). The clinical worldwide use of VMAT is increasing significantly. Currently the majority of published data on VMAT are limited to planning and feasibility studies, although there is emerging clinical outcome data in several tumour sites. This article aims to discuss the current use of VMAT techniques in practice and review the available data from planning and clinical outcome studies in various tumour sites including prostate, pelvis (lower gastrointestinal, gynaecological), head and neck, thoracic, central nervous system, breast and other tumour sites.
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            Effectiveness of noncoplanar IMRT planning using a parallelized multiresolution beam angle optimization method for paranasal sinus carcinoma.

            To determine the effectiveness of noncoplanar beam configurations and the benefit of plans using fewer but optimally placed beams designed by a parallelized multiple-resolution beam angle optimization (PMBAO) approach. The PMBAO approach uses a combination of coplanar and noncoplanar beam configurations for intensity-modulated radiation therapy (IMRT) treatment planning of paranasal sinus cancers. A smaller number of beams (e.g. 3) are first used to explore the solution space to determine the best and worst beam directions. The results of this exploration are then used as a starting point for determining an optimum beam orientation configuration with more beams (e.g. 5). This process is parallelized using a message passing interface, which greatly reduces the overall computation time for routine clinical practice. To test this approach, treatment for 10 patients with paranasal sinus cancer was planned using a total of 5 beams from a pool of 46 possible beam angles. The PMBAO treatment plans were also compared with IMRT plans designed using 9 equally spaced coplanar beams, which is the standard approach in our clinic. Plans with these two different beam configurations were compared with respect to dose conformity, dose heterogeneity, dose-volume histograms, and doses to organs at risk (i.e., eyes, optic nerve, optic chiasm, and brain). The noncoplanar beam configuration was superior in most paranasal sinus carcinoma cases. The target dose homogeneity was better using a PMBAO 5-beam configuration. However, the dose conformity using PMBAO was not improved and was case dependent. Compared with the 9-beam configuration, the PMBAO configuration significantly reduced the mean dose to the eyes and optic nerves and the maximum dose to the contralateral optical path (e.g. the contralateral eye and optic nerve). The maximum dose to the ipsilateral eye and optic nerve was also lower using the PMBAO configuration than using the 9-beam configuration, although this difference was not significant. The mean doses to the optic chiasm and brain are marginally lower using the PMBAO configuration than using 9-beam configuration. The maximum doses to the optic chiasm and brain are the same with the PMBAO configuration and the 9-beam configuration. Parallelized multiple-resolution beam angle optimization with an optimized noncoplanar beam configuration is an effective and practical approach for IMRT treatment planning. Five-beam treatment plans optimized using the PMBAO are at least equivalent to, and overall better than, the plans using 9 equally spaced coplanar beams.
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              Impact of prolonged fraction delivery times on tumor control: a note of caution for intensity-modulated radiation therapy (IMRT).

              Intensity-modulated radiation therapy (IMRT) allows greater dose conformity to the tumor target. However, IMRT, especially static delivery, usually requires more time to deliver a dose fraction than conventional external beam radiotherapy (EBRT). The purpose of this work is to explore the potential impact of such prolonged fraction delivery times on treatment outcome. The generalized linear-quadratic (LQ) model, which accounts for sublethal damage repair and clonogen proliferation, was used to calculate the cell-killing efficiency of various simulated and clinical IMRT plans. LQ parameters derived from compiled clinical data for prostate cancer (alpha = 0.15 Gy(-1), alpha/beta = 3.1 Gy, and a 16-min repair half-time) were used to compute changes in the equivalent uniform dose (EUD) and tumor control probability (TCP) due to prolonged delivery time of IMRT as compared with conventional EBRT. EUD and TCP calculations were also evaluated for a wide range of radiosensitivity parameters. The effects of fraction delivery times ranging from 0 to 45 min on cell killing were studied. Our calculations indicate that fraction delivery times in the range of 15-45 min may significantly decrease cell killing. For a prescription dose of 81 Gy in 1.8 Gy fractions, the EUD for prostate cancer decreases from 78 Gy for a conventional EBRT to 69 Gy for an IMRT with a fraction delivery time of 30 min. The values of EUD are sensitive to the alpha/beta ratio, the repair half-time, and the fraction delivery time. The instantaneous dose-rate, beam-on time, number of leaf shapes (segments), and leaf-sequencing patterns given the same overall fraction delivery time were found to have negligible effect on cell killing. The total time to deliver a single fraction may have a significant impact on IMRT treatment outcome for tumors with a low alpha/beta ratio and a short repair half-time, such as prostate cancer. These effects, if confirmed by clinical studies, should be considered in designing IMRT treatments.
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                Author and article information

                Journal
                Strahlentherapie und Onkologie
                Strahlenther Onkol
                Springer Nature
                0179-7158
                1439-099X
                January 2015
                October 8 2014
                : 191
                : 1
                : 34-42
                Article
                10.1007/s00066-014-0760-8
                25293728
                4b9fc79c-3b3d-4050-ab9c-a19c84225c41
                © 2014
                History

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