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      Evaluation of the hybrid-dynamic conformal arc therapy technique for radiotherapy of lung cancer

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          Abstract

          Purpose

          A hybrid-dynamic conformal arc therapy (HDCAT) technique consisting of a single half-rotated dynamic conformal arc beam and static field-in-field beams in two directions was designed and evaluated in terms of dosimetric benefits for radiotherapy of lung cancer.

          Materials and Methods

          This planning study was performed in 20 lung cancer cases treated with the VERO system (BrainLAB AG, Feldkirchen, Germany). Dosimetric parameters of HDCAT plans were compared with those of three-dimensional conformal radiotherapy (3D-CRT) plans in terms of target volume coverage, dose conformity, and sparing of organs at risk.

          Results

          HDCAT showed better dose conformity compared with 3D-CRT (conformity index: 0.74 ± 0.06 vs. 0.62 ± 0.06, p < 0.001). HDCAT significantly reduced the lung volume receiving more than 20 Gy (V 20: 21.4% ± 8.2% vs. 24.5% ± 8.8%, p < 0.001; V 30: 14.2% ± 6.1% vs. 15.1% ± 6.4%, p = 0.02; V 40: 8.8% ± 3.9% vs. 10.3% ± 4.5%, p < 0.001; and V 50: 5.7% ± 2.7% vs. 7.1% ± 3.2%, p < 0.001), V 40 and V 50 of the heart (V 40: 5.2 ± 3.9 Gy vs. 7.6 ± 5.5 Gy, p < 0.001; V 50: 1.8 ± 1.6 Gy vs. 3.1 ± 2.8 Gy, p = 0.001), and the maximum spinal cord dose (34.8 ± 9.4 Gy vs. 42.5 ± 7.8 Gy, p < 0.001) compared with 3D-CRT.

          conclusions

          HDCAT could achieve highly conformal target coverage and reduce the doses to critical organs such as the lung, heart, and spinal cord compared to 3D-CRT for the treatment of lung cancer patients.

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          Most cited references23

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          Analysis of clinical and dosimetric factors associated with treatment-related pneumonitis (TRP) in patients with non-small-cell lung cancer (NSCLC) treated with concurrent chemotherapy and three-dimensional conformal radiotherapy (3D-CRT).

          To investigate factors associated with treatment-related pneumonitis in non-small-cell lung cancer patients treated with concurrent chemoradiotherapy. We retrospectively analyzed data from 223 patients treated with definitive concurrent chemoradiotherapy. Treatment-related pneumonitis was graded according to Common Terminology Criteria for Adverse Events version 3.0. Univariate and multivariate analyses were performed to identify predictive factors. Median follow-up was 10.5 months (range, 1.4-58 months). The actuarial incidence of Grade > or =3 pneumonitis was 22% at 6 months and 32% at 1 year. By univariate analyses, lung volume, gross tumor volume, mean lung dose, and relative V5 through V65, in increments of 5 Gy, were all found to be significantly associated with treatment-related pneumonitis. The mean lung dose and rV5-rV65 were highly correlated (p or =3 pneumonitis in the group with V5 42% were 3% and 38%, respectively (p = 0.001). In this study, a number of clinical and dosimetric factors were found to be significantly associated with treatment-related pneumonitis. However, rV5 was the only significant factor associated with this toxicity. Until it is better understood which dose range is most relevant, multiple clinical and dosimetric factors should be considered in treatment planning for non-small-cell lung cancer patients receiving concurrent chemoradiotherapy.
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            Radiation pneumonitis as a function of mean lung dose: an analysis of pooled data of 540 patients.

            To determine the relation between the incidence of radiation pneumonitis and the three-dimensional dose distribution in the lung. In five institutions, the incidence of radiation pneumonitis was evaluated in 540 patients. The patients were divided into two groups: a Lung group, consisting of 399 patients with lung cancer and 1 esophagus cancer patient and a Lymph./Breast group with 78 patients treated for malignant lymphoma, 59 for breast cancer, and 3 for other tumor types. The dose per fraction varied between 1.0 and 2.7 Gy and the prescribed total dose between 20 and 92 Gy. Three-dimensional dose calculations were performed with tissue density inhomogeneity correction. The physical dose distribution was converted into the biologically equivalent dose distribution given in fractions of 2 Gy, the normalized total dose (NTD) distribution, by using the linear quadratic model with an alpha/beta ratio of 2.5 and 3.0 Gy. Dose-volume histograms (DVHs) were calculated considering both lungs as one organ and from these DVHs the mean (biological) lung dose, NTDmean, was obtained. Radiation pneumonitis was scored as a complication when the pneumonitis grade was grade 2 (steroids needed for medical treatment) or higher. For statistical analysis the conventional normal tissue complication probability (NTCP) model of Lyman (with n=1) was applied along with an institutional-dependent offset parameter to account for systematic differences in scoring patients at different institutions. The mean lung dose, NTDmean, ranged from 0 to 34 Gy and 73 of the 540 patients experienced pneumonitis, grade 2 or higher. In all centers, an increasing pneumonitis rate was observed with increasing NTDmean. The data were fitted to the Lyman model with NTD50=31.8 Gy and m=0.43, assuming that for all patients the same parameter values could be used. However, in the low dose range at an NTDmean between 4 and 16 Gy, the observed pneumonitis incidence in the Lung group (10%) was significantly (p=0.02) higher than in the Lymph./Breast group (1.4%). Moreover, between the Lung groups of different institutions, also significant (p=0.04) differences were present: for centers 2, 3, and 4, the pneumonitis incidence was about 13%, whereas for center 5 only 3%. Explicitly accounting for these differences by adding center-dependent offset values for the Lung group, improved the data fit significantly (p < 10(-5)) with NTD50=30.5+/-1.4 Gy and m=0.30+/-0.02 (+/-1 SE) for all patients, and an offset of 0-11% for the Lung group, depending on the center. The mean lung dose, NTDmean, is relatively easy to calculate, and is a useful predictor of the risk of radiation pneumonitis. The observed dose-effect relation between the NTDmean and the incidence of radiation pneumonitis, based on a large clinical data set, might be of value in dose-escalating studies for lung cancer. The validity of the obtained dose-effect relation will have to be tested in future studies, regarding the influence of confounding factors and dose distributions different from the ones in this study.
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              An experimental investigation on intra-fractional organ motion effects in lung IMRT treatments.

              Respiration-induced tumour motion can potentially compromise the use of intensity-modulated radiotherapy (IMRT) as a dose escalation tool for lung tumour treatment. We have experimentally investigated the intra-fractional organ motion effects in lung IMRT treatments delivered by multi-leaf collimator (MLC). An in-house made motor-driven platform, which moves sinusoidally with an amplitude of 1 cm and a period of 4 s, was used to mimic tumour motion. Tumour motion was simulated along cranial-caudal direction while MLC leaves moved across the patient from left to right, as in most clinical cases. The dose to a point near the centre of the tumour mass was measured according to geometric and dosimetric parameters from two five-field lung IMRT plans. For each field, measurement was done for two dose rates (300 and 500 MU min(-1)), three MLC delivery modes (sliding window, step-and-shoot with 10 and 20 intensity levels) and eight equally spaced starting phases of tumour motion. The dose to the measurement point delivered from all five fields was derived for both a single fraction and 30 fractions by randomly sampling from measured dose values of each field at different initial phases. It was found that the mean dose to a moving tumour differs slightly (<2-3%) from that to a static tumour. The variation in breathing phase at the start of dose delivery results in a maximum variation around the mean dose of greater than 30% for one field. The full width at half maximum for the probability distribution of the point dose is up to 8% for all five fields in a single fraction, but less than 1-2% after 30 fractions. In general, lower dose rate can reduce the motion-caused dose variation and therefore might be preferable for lung IMRT when no motion mitigation techniques are used. From the two IMRT cases we studied where tumour motion is perpendicular to MLC leaf motion, the dose variation was found to be insensitive to the MLC delivery mode.
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                Author and article information

                Journal
                Radiat Oncol J
                Radiat Oncol J
                ROJ
                Radiation Oncology Journal
                The Korean Society for Radiation Oncology
                2234-1900
                2234-3164
                September 2018
                30 September 2018
                : 36
                : 3
                : 241-247
                Affiliations
                [1 ]Department of Radiation Oncology, Kyungpook National University Chilgok Hospital, Daegu, Korea
                [2 ]Department of Radiation Oncology, School of Medicine, Kyungpook National University, Daegu, Korea
                [3 ]Department of Radiation Oncology, Kyungpook National University Hospital, Daegu, Korea
                Author notes
                Correspondence: Min Kyu Kang, MD, Department of Radiation Oncology, Kyungpook National University Chilgok Hospital, 807 Hoguk-ro, Buk-gu, Daegu 41404, Korea. Tel: +82-53-200-2653, Fax: +82-53-200-2029, E-mail: mkkang@ 123456knu.ac.kr
                [*]

                Both authors contributed equally to this work.

                Article
                roj-2018-00171
                10.3857/roj.2018.00171
                6226139
                30309216
                6bbd76b4-87a3-47c5-a050-2653a795c1b2
                Copyright © 2018. The Korean Society for Radiation Oncology

                This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License ( http://creativecommons.org/licenses/by-nc/4.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

                History
                : 30 March 2018
                : 16 July 2018
                : 16 August 2018
                Categories
                Original Article
                Physics Contribution

                Oncology & Radiotherapy
                lung neoplasms,radiotherapy planning,three-dimensional conformal radiotherapy,arc therapy

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