Dosimetric advantage of volumetric modulated arc therapy in the treatment of intraocular cancer

Deng et al. Radiation Oncology (2017) 12:83 DOI 10.1186/s13014-017-0819-7 RESEARCH Open Access Dosimetric advantage of volumetric modulated arc therapy in the treatment of intraocular cancer Zhenxiang Deng†, Lanxiao Shen†, Xiaomin Zheng, Yongqiang Zhou, Jinling Yi, Ce Han, Congying Xie and Xiance Jin* Abstract Objective: The purpose of this study is to investigate the dosimetric advantages of volumetric modulated arc therapy (VMAT) in the treatment of intraocular cancer by comparing it directly with three-dimensional conformal radiotherapy (CRT) and intensity-modulated radiotherapy (IMRT). Methods: CRT plan, 7f-IMRT plan, and one-arc VMAT plan were generated for 14 intraocular cancer patients. Dosimetric and biological quality indices for target volume and organs at risks (OARs) were evaluated and compared. Results: The target coverage presented by V95 for CRT, IMRT and VMAT were 95.02% ± 0.67%, 95.51% ± 2.25%, and 95.92% ± 3.05%, respectively. The homogeneity index (HI) for CRT, IMRT and VMAT were 0.15 ± 0.05, 0.23 ± 0.05, and 0.23 ± 0.06, respectively. IMRT and VMAT greatly decreased the dose to ipsilateral lens compared with CRT with a D1 of 2972.66 ± 1407.12 cGy, 3317.82 ± 915.28 cGy and 4809.54 ± 524.60 cGy for IMRT, VMAT and CRT, respectively. Similar results were observed for ipsilateral eyeballs. IMRT and VMAT also spared better on brainstem, optical nerves and optical chiasm compared CRT. However, CRT achieved lower dose to the eyeballs compared with IMRT and VMAT. VMAT and IMRT showed mixed results on target coverage and OAR sparing. The average MUs and delivery time of IMRT and VMAT were 531.25 ± 81.21 vs. 400.99 ± 61.49 and 5.05 ± 0.53 vs.1.71 ± 0.69 min, respectively. Conclusions: Although no clear distinction on PTV coverage among CRT, IMRT and VMAT plans was observed in the treatment of intraocular cancer, VMAT and IMRT achieved better homogeneity and conformity for target volume, and delivered fewer doses to ipsilateral lens and eyeballs compared with CRT. However, VMAT and IMRT increased the low dose volume to the contralateral OARs. Although VMAT and IMRT showed mixed results on target coverage and OAR sparing, VMAT decreased MU and delivery time significantly compared with IMRT. VMAT is a promising and feasible external beam radiotherapy technique in the treatment of intraocular cancer patients. Keywords: Intraocular cancer, Conformal radiotherapy, Intensity-modulated radiotherapy, Volumetric-modulated radiotherapy * Correspondence: † Equal contributors Radiotherapy and Chemotherapy Department, the 1st Affiliated Hospital of Wenhzou Medical University, No.2 Fuxue Lane, Wenzhou 325000, China © The Author(s). 2017 Open Access This 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. Deng et al. Radiation Oncology (2017) 12:83 Introduction Intraocular cancer, which includes primary and secondary intraocular cancers, presents a therapeutic challenge due to the sensitive tissues involved and the necessity to destroy the tumor while minimizing visual loss. Primary intraocular cancers start inside the eyeball. In adults, melanoma is the most common primary intraocular cancer. In children, retinoblastoma (a cancer arising from cells in the retina) is the most common primary intraocular cancer, and medulloepithelioma is the next most common [1]. Secondary intraocular cancers start somewhere else and then spread to the eye, which are actually more common than primary intraocular cancers. The most common cancers that spread to the eye are breast and lung cancers [2]. Local therapy options for management of intraocular disease include enucleation, radiation therapy (RT), cryotherapy, and laser therapy [3]. Radiation therapy (RT) had been well described in the management of orbital lymphoma [4–8]. External beam radiation therapy (EBRT) is currently considered the most common treatment modality for intraocular cancer, which provides lower late recurrence rates with respect to radioactive plaque brachytherapy [9]. EBRT also has an advantage over surgery by preserving the eye structure, which may result in a better appearance after treatment. The main concern with radiation therapy is damage to parts of the eye, leading to problems such as cataracts, retinal detachment, glaucoma, or bleeding into the eye [10–12]. The delivery of radiotherapy to orbit is technically challenging given the critical structures in the treatment field and their relatively low tolerance levels. In the past, a single enface electron beam or AP beam was used in the radiotherapy. The radiation is often delivered using wedged anterior and lateral fields directed at the target volume. This technique causes significant fluctuations in dose homogeneity within the treatment field, often with hotspots of more than 25%. The conventional RT often causes acute side effects in many patients and induces dry eye syndrome and conjunctivitis [4]. A dose reduction to the critical structures during radiotherapy had been a concern of physicians. Advances in RT technology, such as proton therapy, intensity-modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT) allow more conformal dose distributions for patients with intraocular cancer [13, 14]. The unique dosimetric properties of IMRT and VMAT have the potential to reduce the injury to uninvolved structures while attaining appropriate tumor coverage and may lead to an improved therapeutic index with respect to tumor control and toxicity [15–17]. Particularly, VMAT technique had gained enormous interest world-wide by using continuous changing MLC movement, gantry rotation and dose rate with less MUs and Page 2 of 7 delivery time [18, 19]. VMAT improves dose homogeneity and sparing of critical organs over IMRT for many tumor sites [16, 17, 19]. Eldebawy et al compared the dosimetric distributions among radiotherapy techniques, including electron beam, photon beam with wedge pair, 3D-CRT, IMRT, VMAT, fractionated stereotactic radiotherapy, and helical tomotherapy in three retinoblastoma patients. They concluded that inverse planned image-guided radiotherapy using tomotherapy or VMAT obtained a better conformity index, a lower integral dose and improved orbital bone and brain sparing compared with other techniques [20]. Except for this study, few further study had been carried out to explore the dosimetric advantage of VMAT in the treatment of intraocular cancer patients. 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