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      Single arc volumetric-modulated arc therapy is sufficient for nasopharyngeal carcinoma: a dosimetric comparison with dual arc VMAT and dynamic MLC and step-and-shoot intensity-modulated radiotherapy

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          Abstract

          Background

          The performance of single arc VMAT (VMAT1) for nasopharyngeal carcinoma (NPC) on the Axesse linac has not been well described in previous studies. The purpose of this study is to assess the feasibility of VMAT1 for NPC by comparing the dosimetry, delivery efficiency, and accuracy with dual arc VMAT (VMAT2), dynamic MLC intensity-modulated radiotherapy (dIMRT), and step-and-shoot intensity-modulated radiotherapy (ssIMRT).

          Methods

          Twenty consecutive patients with non-metastatic NPC were selected to be planned with VMAT1, VMAT2, dIMRT and ssIMRT using Monaco 3.2 TPS on the Axesse™ linear accelerator. Three planning target volumes (PTVs), contoured as high risk, moderate risk and low risk regions, were set to receive median absorbed-dose (D 50%) of 72.6 Gy, 63.6 Gy and 54 Gy, respectively. The Homogeneity Index (HI), Conformity Index (CI), Dose Volume Histograms (DVHs), delivery efficiency and accuracy were all evaluated.

          Results

          Mean HI of PTV 72.6 is better with VMAT1(0.07) and VMAT2(0.07) than dIMRT(0.09) and ssIMRT(0.09). Mean HI of PTV 63.6 is better with VMAT1(0.21) and VMAT2(0.21) than dIMRT and ssIMRT. Mean CI of PTV 72.6 is also better with VMAT1(0.57) and VMAT2(0.57) than dIMRT(0.49) and ssIMRT(0.5). Mean CI of PTV 63.6 is better with VMAT1(0.76) and VMAT2(0.76) than dIMRT(0.73) and ssIMRT(0.73). VMAT had significantly improved homogeneity and conformity compared with IMRT. There was no significant difference between VMAT1 and VMAT2 in PTV coverage. Dose to normal tissues was acceptable for all four plan groups. VMAT1 and VMAT2 showed no significant difference in normal tissue sparring, whereas the mean dose of the parotid gland of dIMRT was significantly reduced compared to VMAT1 and VMAT2. The mean delivery time for VMAT1, VMAT2, dIMRT and ssIMRT was 2.7 min, 3.9 min, 5.7 min and 14.1 min, respectively. VMAT1 reduced the average delivery time by 29.8%, 51.1% and 80.8% compared with VMAT2, dIMRT and ssIMRT, respectively. VMAT and IMRT could all be delivered accurately based on our quality assurance standards.

          Conclusions

          In the treatment of NPC using the Axesse™ linear accelerator, single arc VMAT has shown superiority to double arc VMAT, dIMRT and ssIMRT in delivery efficiency, without compromise to the PTV coverage. However, there is still room for improvement in terms of OAR sparing.

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          How does intensity-modulated radiotherapy versus conventional two-dimensional radiotherapy influence the treatment results in nasopharyngeal carcinoma patients?

          Shu-Zhen Lai, Wen-Fei Li, Lei Chen … (2011)
          To compare the results of intensity-modulated radiotherapy (IMRT) with those of two-dimensional conventional radiotherapy (2D-CRT) in the treatment of patients with nasopharyngeal carcinoma (NPC). A retrospective review of data from 1,276 patients with biopsy-proven, nonmetastatic NPC was performed. All patients had undergone magnetic resonance imaging and were staged according to the sixth edition of the American Joint Committee on Cancer staging criteria. Radiotherapy was the primary treatment for all patients. Of the 1,276 patients, 512 were treated with IMRT and 764 with 2D-CRT. The 5-year actuarial local relapse-free survival (LRFS), the nodal relapse-free survival (NRFS), the distant metastasis-free survival (DMFS), and the disease-free survival (DFS) rates were 92.7%, 97.0%, 84.0%, and 75.9%, respectively, for the IMRT group, and 86.8%, 95.5%, 82.6%, and 71.4%, respectively, for the 2D-CRT group. In stage T1 patients, improvement of LRFS in the IMRT group was even significantly higher than in the 2D-CRT group (100% vs. 94.4%; p = 0.016). A trend of improvement of DFS was observed in the IMRT group compared with the 2D-CRT group but without reaching statistical significance. NRFS and DMFS rates were similar in the two groups. A greater improvement of treatment results with IMRT than with 2D-CRT was demonstrated primarily by achieving a higher local tumor control rate in NPC patients, especially in the early T stage patients. The goal of better control of both local failure in advanced, nonmetastatic NPC patients and of distant failure should be addressed in future studies. Copyright © 2011 Elsevier Inc. All rights reserved.
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            Volumetric modulated arc therapy: IMRT in a single gantry arc.

            Karl-Otto Bischoff (2007)
            In this work a novel plan optimization platform is presented where treatment is delivered efficiently and accurately in a single dynamically modulated arc. Improvements in patient care achieved through image-guided positioning and plan adaptation have resulted in an increase in overall treatment times. Intensity-modulated radiation therapy (IMRT) has also increased treatment time by requiring a larger number of beam directions, increased monitor units (MU), and, in the case of tomotherapy, a slice-by-slice delivery. In order to maintain a similar level of patient throughput it will be necessary to increase the efficiency of treatment delivery. The solution proposed here is a novel aperture-based algorithm for treatment plan optimization where dose is delivered during a single gantry arc of up to 360 deg. The technique is similar to tomotherapy in that a full 360 deg of beam directions are available for optimization but is fundamentally different in that the entire dose volume is delivered in a single source rotation. The new technique is referred to as volumetric modulated arc therapy (VMAT). Multileaf collimator (MLC) leaf motion and number of MU per degree of gantry rotation is restricted during the optimization so that gantry rotation speed, leaf translation speed, and dose rate maxima do not excessively limit the delivery efficiency. During planning, investigators model continuous gantry motion by a coarse sampling of static gantry positions and fluence maps or MLC aperture shapes. The technique presented here is unique in that gantry and MLC position sampling is progressively increased throughout the optimization. Using the full gantry range will theoretically provide increased flexibility in generating highly conformal treatment plans. In practice, the additional flexibility is somewhat negated by the additional constraints placed on the amount of MLC leaf motion between gantry samples. A series of studies are performed that characterize the relationship between gantry and MLC sampling, dose modeling accuracy, and optimization time. Results show that gantry angle and MLC sample spacing as low as 1 deg and 0.5 cm, respectively, is desirable for accurate dose modeling. It is also shown that reducing the sample spacing dramatically reduces the ability of the optimization to arrive at a solution. The competing benefits of having small and large sample spacing are mutually realized using the progressive sampling technique described here. Preliminary results show that plans generated with VMAT optimization exhibit dose distributions equivalent or superior to static gantry IMRT. Timing studies have shown that the VMAT technique is well suited for on-line verification and adaptation with delivery times that are reduced to approximately 1.5-3 min for a 200 cGy fraction.
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              A prospective, randomized study comparing outcomes and toxicities of intensity-modulated radiotherapy vs. conventional two-dimensional radiotherapy for the treatment of nasopharyngeal carcinoma.

              Gang Peng, Tao Wang, Kun-Yu Yang … (2012)
              To compare clinical outcomes and toxicities of two-dimensional conventional radiation therapy (2D-CRT) and intensity modulated radiation therapy (IMRT) for the treatment of nasopharyngeal carcinoma (NPC). Between July 2003 and October 2008, 616 patients with non-metastatic stage I to IVb NPC were prospectively randomized to receive 2D-CRT (n=310; mean age, 44.8±13.6 years) or IMRT (n=306; mean age, 46.7±12.5 years). Clinical outcomes and acute and late toxicities were determined and compared. The 2 groups were comparable with respect to all parameters of demographics and disease characteristics (all, p>0.05). Median follow-up was 42 months (range, 1-83 months). The 5-year actuarial local control rate was 90.5% in the IMRT group and 84.7% in the 2D-CRT group. The local control rates were 91% for stage T3 and 81.5% for stage T4 disease in the IMRT group and 80% and 62.2% in the 2D-CRT group, respectively. The 5-year actuarial nodal relapse-free survival (NRFS) rate was 92.4% in the IMRT and 92.9% in the 2D-CRT group (p>0.05). The NRFS was 93.9% for N2 disease in the IMRT group and 91.4% in the 2D-CRT group (p=0.02). The 5-year overall survival (OS) rate was 79.6% for the IMRT group and 67.1% for the 2D-CRT group (p=0.001). When stratified for stage, a significant difference was only noted for stage III disease. In terms of radiation-induced toxicities, patients in IMRT group had significantly lower radiation-induced toxicities than those in 2D-CRT group. IMRT provides improved local-recurrence free survival, especially in late-stage NPC patients and is associated with a lower incidence of toxicities. Copyright © 2012. Published by Elsevier Ireland Ltd.
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                Author and article information

                Contributors
                Zhong-Hua Ning
                Jin-Ming Mu
                Jian-Xue Jin
                Xiao-Dong Li
                Qi-Lin Li
                Wen-Dong Gu
                Jin Huang
                Yang Han
                Hong-Lei Pei
                Journal
                Journal ID (nlm-ta): Radiat Oncol
                Journal ID (iso-abbrev): Radiat Oncol
                Title: Radiation Oncology (London, England)
                Publisher: BioMed Central
                ISSN (Electronic): 1748-717X
                Publication date Collection: 2013
                Publication date (Electronic): 14 October 2013
                Volume: 8
                Page: 237
                Affiliations
                [1 ]Department of Radiation Oncology, The Third Affiliated Hospital, Soochow University, 185 Juqian Road, Changzhou 213003, China
                [2 ]Department of Radiation Physics, Elekta China Co. Ltd, 27 North Fourth Ring Mid Road, Chaoyang District, Beijing 100101, China
                [3 ]Department of Oncology, The Third Affiliated Hospital, Soochow University, 185 Juqian Road, Changzhou 213003, China
                Article
                Publisher ID: 1748-717X-8-237
                DOI: 10.1186/1748-717X-8-237
                PMC ID: 3854543
                PubMed ID: 24125432
                SO-VID: 3b9e4da8-a4b6-48da-9cfe-9cd0133a27ca
                Copyright © Copyright © 2013 Ning et al.; licensee BioMed Central Ltd.
                License:

                This is an open access article distributed under the terms of the Creative Commons Attribution License ( http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

                History
                Date received : 27 May 2013
                Date accepted : 5 October 2013
                Categories
                Subject: Research

                ScienceOpen disciplines: Oncology & Radiotherapy
                Keywords: radiotherapy,volumetric modulated arc therapy,intensity modulated,nasopharyngeal carcinoma,plan evaluation,dosimetry
                Data availability:
                ScienceOpen disciplines: Oncology & Radiotherapy
                Keywords: radiotherapy, volumetric modulated arc therapy, intensity modulated, nasopharyngeal carcinoma, plan evaluation, dosimetry

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