title: Optimal technique of linear accelerator-based stereotactic radiosurgery for tumors adjacent to brainstem.
abstract: Stereotactic radiosurgery (SRS) is a well-established technique that is replacing whole-brain irradiation in the treatment of intracranial lesions, which leads to better preservation of brain functions, and therefore a better quality of life for the patient. There are several available forms of linear accelerator (LINAC)-based SRS, and the goal of the present study is to identify which of these techniques is best (as evaluated by dosimetric outcomes statistically) when the target is located adjacent to brainstem. We collected the records of 17 patients with lesions close to the brainstem who had previously been treated with single-fraction radiosurgery. In all, 5 different lesion catalogs were collected, and the patients were divided into 2 distance groups-1 consisting of 7 patients with a target-to-brainstem distance of less than 0.5cm, and the other of 10 patients with a target-to-brainstem distance of ≥ 0.5 and < 1cm. Comparison was then made among the following 3 types of LINAC-based radiosurgery: dynamic conformal arcs (DCA), intensity-modulated radiosurgery (IMRS), and volumetric modulated arc radiotherapy (VMAT). All techniques included multiple noncoplanar beams or arcs with or without intensity-modulated delivery. The volume of gross tumor volume (GTV) ranged from 0.2cm(3) to 21.9cm(3). Regarding the dose homogeneity index (HIICRU) and conformity index (CIICRU) were without significant difference between techniques statistically. However, the average CIICRU = 1.09 ± 0.56 achieved by VMAT was the best of the 3 techniques. Moreover, notable improvement in gradient index (GI) was observed when VMAT was used (0.74 ± 0.13), and this result was significantly better than those achieved by the 2 other techniques (p < 0.05). For V4Gy of brainstem, both VMAT (2.5%) and IMRS (2.7%) were significantly lower than DCA (4.9%), both at the p < 0.05 level. Regarding V2Gy of normal brain, VMAT plans had attained 6.4 ± 5%; this was significantly better (p < 0.05) than either DCA or IMRS plans, at 9.2 ± 7% and 8.2 ± 6%, respectively. Owing to the multiple arc or beam planning designs of IMRS and VMAT, both of these techniques required higher MU delivery than DCA, with the averages being twice as high (p < 0.05). If linear accelerator is only 1 modality can to establish for SRS treatment. Based on statistical evidence retrospectively, we recommend VMAT as the optimal technique for delivering treatment to tumors adjacent to brainstem.
authors.affiliation: Department of Biomedical Engineering and Environmental Sciences, National Tsing Hua University, Hsinchu, Taiwan; Department of Radiation Oncology, Taipei Tzu Chi Hospital, Buddhist Tzu Chi Medical Foundation, Taipei, Taiwan. Electronic address: et000417@gmail.com.
authors.forename: Chiou-Shiung
authors.initials: CS
authors.lastname: Chang
authors.affiliation: Department of Radiation Oncology, Taipei Tzu Chi Hospital, Buddhist Tzu Chi Medical Foundation, Taipei, Taiwan; College of Medicine, Tzu Chi University, Hualan, Taiwan.
authors.forename: Jing-Min
authors.initials: JM
authors.lastname: Hwang
authors.affiliation: Division of Neurosurgery, Department of Surgery, Taipei Tzu Chi Hospital, Buddhist Tzu Chi Medical Foundation, Taipei, Taiwan; Department of Surgery, School of Medicine, College of Medicine, Buddhist Tzu Chi University, Hualan, Taiwan.
authors.forename: Po-An
authors.initials: PA
authors.lastname: Tai
authors.affiliation: Department of Radiation Oncology, Taipei Tzu Chi Hospital, Buddhist Tzu Chi Medical Foundation, Taipei, Taiwan; College of Medicine, Tzu Chi University, Hualan, Taiwan.
authors.forename: You-Kang
authors.initials: YK
authors.lastname: Chang
authors.affiliation: Department of Radiation Oncology, Taipei Tzu Chi Hospital, Buddhist Tzu Chi Medical Foundation, Taipei, Taiwan.
authors.forename: Yu-Nong
authors.initials: YN
authors.lastname: Wang
authors.affiliation: Department of Radiation Oncology, New York-Presbyterian Hospital, New York, NY.
authors.forename: Rompin
authors.initials: R
authors.lastname: Shih
authors.affiliation: Department of Biomedical Engineering and Environmental Sciences, National Tsing Hua University, Hsinchu, Taiwan.
authors.forename: Keh-Shih
authors.initials: KS
authors.lastname: Chuang
mesh_terms: D001932:Brain Neoplasms / Q000532:radiotherapy*; D001933:Brain Stem / Q000473:pathology*; D005260:Female; D006801:Humans; D008297:Male; D058958:Organs at Risk; D010315:Particle Accelerators; D016634:Radiosurgery / Q000379:methods*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*
keywords: Conformity index; Gradient index; Stereotactic radiosurgery; VMAT