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HyperArc VMAT planning for single and multiple brain metastases stereotactic radiosurgery: a new treatment planning approach

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      Abstract

      Purpose

      The HyperArc VMAT (HA-VMAT) planning approach was newly developed to fulfill the demands of dose delivery for brain metastases stereotactic radiosurgery. We compared the dosimetric parameters of the HA-VMAT plan with those of the conventional VMAT (C-VMAT).

      Material and methods

      For 23 patients (1–4 brain metastases), C-VMAT and HA-VMAT plans with a prescription dose of 20–24 Gy were retrospectively generated, and dosimetric parameters for PTV (homogeneity index, HI; conformity index, CI; gradient index, GI) and brain tissue (V 2Gy-V 16Gy) were evaluated. Subsequently, the physical characteristics (modulation complexity score for VMAT, MCSV; Monitor unit, MU) of both treatment approaches were compared.

      Results

      HA-VMAT provided higher HI (1.41 ± 0.07 vs. 1.24 ± 0.07, p < 0.01), CI (0.93 ± 0.02 vs. 0.90 ± 0.05, p = 0.01) and lower GI (3.06 ± 0.42 vs. 3.91 ± 0.55, p < 0.01) values. Moderate-to-low dose spreads (V 4Gy-V 16Gy) were significantly reduced ( p < 0.01) in the HA-VMAT plan over that of C-VMAT. HA-VMAT plans resulted in more complex MLC patterns (lower MCSV, p < 0.01) and higher MU ( p < 0.01).

      Conclusions

      HA-VMAT plans provided significantly higher conformity and rapid dose falloff with respect to the C-VMAT plans.

      Related collections

      Most cited references 25

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      Adjuvant whole-brain radiotherapy versus observation after radiosurgery or surgical resection of one to three cerebral metastases: results of the EORTC 22952-26001 study.

      This European Organisation for Research and Treatment of Cancer phase III trial assesses whether adjuvant whole-brain radiotherapy (WBRT) increases the duration of functional independence after surgery or radiosurgery of brain metastases. Patients with one to three brain metastases of solid tumors (small-cell lung cancer excluded) with stable systemic disease or asymptomatic primary tumors and WHO performance status (PS) of 0 to 2 were treated with complete surgery or radiosurgery and randomly assigned to adjuvant WBRT (30 Gy in 10 fractions) or observation (OBS). The primary end point was time to WHO PS deterioration to more than 2. Of 359 patients, 199 underwent radiosurgery, and 160 underwent surgery. In the radiosurgery group, 100 patients were allocated to OBS, and 99 were allocated to WBRT. After surgery, 79 patients were allocated to OBS, and 81 were allocated to adjuvant WBRT. The median time to WHO PS more than 2 was 10.0 months (95% CI, 8.1 to 11.7 months) after OBS and 9.5 months (95% CI, 7.8 to 11.9 months) after WBRT (P = .71). Overall survival was similar in the WBRT and OBS arms (median, 10.9 v 10.7 months, respectively; P = .89). WBRT reduced the 2-year relapse rate both at initial sites (surgery: 59% to 27%, P < .001; radiosurgery: 31% to 19%, P = .040) and at new sites (surgery: 42% to 23%, P = .008; radiosurgery: 48% to 33%, P = .023). Salvage therapies were used more frequently after OBS than after WBRT. Intracranial progression caused death in 78 (44%) of 179 patients in the OBS arm and in 50 (28%) of 180 patients in the WBRT arm. After radiosurgery or surgery of a limited number of brain metastases, adjuvant WBRT reduces intracranial relapses and neurologic deaths but fails to improve the duration of functional independence and overall survival.
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        Stereotactic radiosurgery plus whole brain radiotherapy versus radiotherapy alone for patients with multiple brain metastases.

        Multiple brain metastases are a common health problem, frequently diagnosed in patients with cancer. The prognosis, even after treatment with whole brain radiation therapy (WBRT), is poor with average expected survivals less than 6 months. Retrospective series of stereotactic radiosurgery have shown local control and survival benefits in case series of patients with solitary brain metastases. We hypothesized that radiosurgery plus WBRT would provide improved local brain tumor control over WBRT alone in patients with two to four brain metastases. Patients with two to four brain metastases (all < or =25 mm diameter and known primary tumor type) were randomized to initial brain tumor management with WBRT alone (30 Gy in 12 fractions) or WBRT plus radiosurgery. Extent of extracranial cancer, tumor diameters on MRI scan, and functional status were recorded before and after initial care. The study was stopped at an interim evaluation at 60% accrual. Twenty-seven patients were randomized (14 to WBRT alone and 13 to WBRT plus radiosurgery). The groups were well matched to age, sex, tumor type, number of tumors, and extent of extracranial disease. The rate of local failure at 1 year was 100% after WBRT alone but only 8% in patients who had boost radiosurgery. The median time to local failure was 6 months after WBRT alone (95% confidence interval [CI], 3.5-8.5) in comparison to 36 months (95% CI, 15.6-57) after WBRT plus radiosurgery (p = 0.0005). The median time to any brain failure was improved in the radiosurgery group (p = 0.002). Tumor control did not depend on histology (p = 0.85), number of initial brain metastases (p = 0.25), or extent of extracranial disease (p = 0.26). Patients who received WBRT alone lived a median of 7.5 months, while those who received WBRT plus radiosurgery lived 11 months (p = 0.22). Survival did not depend on histology or number of tumors, but was related to extent of extracranial disease (p = 0.02). There was no neurologic or systemic morbidity related to stereotactic radiosurgery. Combined WBRT and radiosurgery for patients with two to four brain metastases significantly improves control of brain disease. WBRT alone does not provide lasting and effective care for most patients.
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          A simple dose gradient measurement tool to complement the conformity index.

           I Paddick,  B Lippitz (2006)
          A dose gradient index (GI) is proposed that can be used to compare treatment plans of equal conformity. The steep dose gradient outside the radiosurgical target is one of the factors that makes radiosurgery possible. It therefore makes sense to measure this variable and to use it to compare rival plans, explore optimal prescription isodoses, or compare treatment modalities. The GI is defined as the ratio of the volume of half the prescription isodose to the volume of the prescription isodose. For a plan normalized to the 50% isodose line, it is the ratio of the 25% isodose volume to that of the 50% isodose volume. The GI will differentiate between plans of similar conformity, but with different dose gradients, for example, where isocenters have been inappropriately centered on the edge of the target volume. In a retrospective series of 50 dose plans for the treatment of vestibular schwannoma, the optimal prescription isodose was assessed. A mean value of 40% (median 38%, range 30-61%) was calculated, not 50% as might be anticipated. The GI can show which of these prescription isodoses will give the steepest dose falloff outside the target. When planning a multiisocenter treatment, there may be a temptation to place some isocenters on the edge of the target. This has the apparent advantage of producing a plan of good conformity and a predictable prescription isodose; however, it risks creating a plan that has a low dose gradient outside the target. The quality of this dose gradient is quantified by the GI.
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            Author and article information

            Affiliations
            [1 ]Department of Radiation Oncology, Osaka International Cancer Institute, 3-1-69 Otemae, Chuo-ku, Osaka, 537-8567 Japan
            [2 ]ISNI 0000 0004 0373 3971, GRID grid.136593.b, Department of Medical Physics and Engineering, , Osaka University Graduate School of Medicine, ; 1-7 Yamadaoka, Suita, Osaka, 565-0871 Japan
            [3 ]ISNI 0000 0004 0403 4283, GRID grid.412398.5, Division of Medical Physics, Oncology Center, , Osaka University Hospital, ; 2-2 (D10) Yamadaoka, Suita, Osaka, 565-0871 Japan
            [4 ]Department of Radiation Oncology, Yao Municipal Hospital, 1-3-1 Ryuge-cho, Yao, Osaka, 581-0069 Japan
            Contributors
            ueyama-si@mc.pref.osaka.jp
            ueda-yo@mc.pref.osaka.jp
            akino-radonc@umin.net
            misaki.hashimoto@hosp-yao.osaka.jp
            masaoka-ak@mc.pref.osaka.jp
            hirata-ta@mc.pref.osaka.jp
            miyazaki-ma@mc.pref.osaka.jp
            koizumi@sahs.med.osaka-u.ac.jp
            (+81)-6-6945-1181 , teshima-te@mc.pref.osaka.jp
            Journal
            Radiat Oncol
            Radiat Oncol
            Radiation Oncology (London, England)
            BioMed Central (London )
            1748-717X
            29 January 2018
            29 January 2018
            2018
            : 13
            29378610 5789615 948 10.1186/s13014-017-0948-z
            © The Author(s). 2018

            Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License ( http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. 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.

            Funding
            Funded by: Health and Labour Sciences Research Grants for Promotion of Cancer Control Programs
            Award ID: H26-Cancer Policy-General-014
            Award Recipient :
            Funded by: JSPS KAKENHI Grant
            Award ID: 15H04913
            Award ID: 17K15816
            Award Recipient :
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            Research
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            © The Author(s) 2018

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