The feasibility of using coplanar-only VMAT combined with “Treat” function to replace non-coplanar VMAT for SRS of 2 to 6 brain metastases

Introduction

Approximately 20% to 40% of non-small cell lung cancer (NSCLC) patients develop brain metastases (BMs), with 70% presenting with multiple lesions (1,2). In recent years, the treatment paradigm for multiple BMs has shifted from whole-brain radiotherapy (WBRT) to stereotactic radiosurgery (SRS) because of its superior local control (LC), comparable overall survival, and reduced neurocognitive toxicity (3-5).

Recent advances in radiotherapy technology have enabled the implementation of frameless linear accelerator (Linac)-based single-isocenter volumetric modulated arc therapy (VMAT) for SRS of multiple BMs (6,7). This approach significantly reduces the overall treatment time (OTT), enhances patient comfort and improves the clinical workflow while achieving plan quality comparable to or better than that of conventional multi-isocenter techniques (8-10). Although single-isocenter multitarget VMAT provides significant benefits, the persistent challenge of the “island blocking” problem (11) continues to be a concern. This problem arises when two or more tumors are aligned along the motion direction of the multileaf collimator (MLC), leading to increased low- and intermediate-dose spills. Many investigators have sought to address this challenge through collimator angle optimization (12-14), which has been proven effective in reducing the radiation dose to normal brain tissue (NBT). However, in certain multitarget cases, collimator optimization alone is insufficient to mitigate the “island blocking” problem, as illustrated in Figure 1, necessitating the addition of couch angle optimization.

Figure 1 An example illustrating MLC patterns with various collimator angles (10° angle interval) in coplanar volumetric modulated arc therapy for intracranial multiple BMs (5 lesions, circles). Note that the “island blocking” problem always exists (red arrows) in the absence of noncoplanar treatment fields. BMs, brain metastases; MLC, multileaf collimator.

However, the use of noncoplanar VMAT (NC-VMAT) may introduce additional setup errors due to couch rotations, potentially compromising target coverage or leading to excessive dose exposure to organs at risk (OARs) (15-17). Furthermore, many cancer centers also face limitations in available image-guided radiotherapy (IGRT) techniques for noncoplanar setup verification. While surface-guided radiotherapy (SGRT) systems, such as the catalyst HD^TM (C-RAD Positioning AB, Uppsala, Sweden), offer the potential for noncoplanar setup verification (18,19), several studies (20-22) have demonstrated that its noncoplanar positioning accuracy is inferior to that of coplanar positioning.

Recently, the newly released RayStation treatment planning system (TPS; version 13B; RaySearch Laboratories) has introduced the “Treat” function, in which each arc can be assigned to irradiate specific target(s), regardless of the number and spatial distribution of targets. This indicates that coplanar-only VMAT combined with the “Treat” function (TREAT-CO-VMAT) can effectively address the “island blocking” problem. However, few studies have assessed whether the TREAT-CO-VMAT can offer dosimetric advantages. Therefore, this study aims to systematically evaluate and compare the dosimetric performance of the TREAT-CO-VMAT with that of the conventional single-isocenter NC-VMAT SRS for multiple BMs. We present this article in accordance with the STROBE reporting checklist (available at https://qims.amegroups.com/article/view/10.21037/qims-2025-570/rc).

Methods

Patients

The study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. This study was reviewed and approved by the ethics committee of the West China Hospital (Approval number: 2019535) and individual consent for this retrospective analysis was waived. 11 patients with 2 to 6 intracranial lesions who underwent conventional single-isocenter NC-VMAT SRS treatment from July 2019 to October 2023 were retrospectively studied in this work. Patient and tumor characteristics are provided in Table 1.

All patients were immobilized in the head-first supine position via a thermoplastic mask for simulation. To define the gross tumor volume (GTV), all patients underwent T1-weighted magnetic resonance imaging (MRI) with gadolinium contrast and high-resolution computed tomography (CT) scans, both of which were acquired with a 1 mm slice thickness. The planning target volume (PTV) was derived via a 1 mm expansion from the GTV. All individual PTVs of each patient were combined into a PTV_total for dosimetric evaluation. OARs, including the lenses, basal ganglia, brainstem, optic nerves, spinal cord, eyeballs and optic chiasma, were contoured. In this study, NBT was defined as the brain volume excluding the PTV_total. The prescription dose (D_p) was 18–20 Gy delivered in a single fraction. All plans were normalized so that D_p covered 98% of the PTV_total. The time interval between CT/MRI simulation and treatment was kept at a minimum, with a strict requirement not to exceed 7 days.

Treatment linac

All patients were treated with an Edge linac (Varian, Palo Alto, CA, USA), which was equipped with a 6D robotic couch for precise correction of rotational setup errors. This Linac supports flattening filter-free (FFF) delivery mode, with maximum dose rates of 2,400 monitor units (MUs)/min for 10 MV FFF beams and 1,400 MUs/min for 6 MV FFF beams, which can significantly shorten the beam-on time (BOT). The system features a high-definition MLC with 2.5-mm leaf widths within ±4 cm of the isocenter and 5-mm leaves beyond this range. Additionally, MLC leaf interdigitation is supported, allowing for enhanced modulation and dose conformity.

Conventional NC-VMAT planning

The clinically implemented treatment plan, namely, the conventional single-isocenter NC-VMAT plan, was designed via an earlier version of the RayStation TPS (version 4.7; RaySearch Laboratories), where the “Treat” function was unavailable. The treatment isocenter was positioned at the geometric center of the PTV_total. The NC-VMAT plan included one 360°coplanar arc and up to three 180° noncoplanar arcs at selected couch angles (315°, 90° and 45°), which were determined on the basis of the number of lesions. Before planning, the collimator angle of each arc was manually adjusted to minimize the “island blocking” problem as much as possible. A 6 MV FFF beam (1,400 MUs/min) was utilized. In our clinical practice, the maximum PTV dose should not exceed 150% of D_p. To achieve a sharp dose gradient, five concentric ring structures around the PTV_total were employed in conjunction with a dose fall-off function. The final dose was calculated via the collapsed cone dose calculation algorithm with a 1 mm grid resolution.

TREAT-CO-VMAT planning

For comparison, each single-isocenter NC-VMAT plan was retrospectively designed via TREAT-CO-VMAT with the updated RayStation TPS (version 13B; RaySearch Laboratories), which incorporates the “Treat” function. The same planning parameters as those used in the clinically applied NC-VMAT plans, including OAR dose constraints, the Linac platform, beam energies, isocenter locations, dose calculation grid resolution, gantry spacing (control points), and final dose normalization, were maintained in the TREAT-CO-VMAT plans. However, unlike the NC-VMAT, the TREAT-CO-VMAT exclusively employs coplanar arcs, with the number of arcs corresponding to the number of lesions. Additionally, the TREAT-CO-VMAT approach applied the “Treat” function to ensure that each arc targets only a single lesion. To enable the use of the “Treat” function, a defined margin must be specified for each target. This margin represents the maximum allowable distance between the ends of the MLC leaves and the target boundary during treatment delivery. Based on our institutional experience, an excessively large “Treat” margin (>0.5 cm) cannot effectively alleviate the “island blocking” issue between closely spaced targets, whereas an excessively small “Treat” margin (<0.3 cm) tends to result in the maximum dose within the PTV exceeding 150% of the Dp. Therefore, a margin of 0.3–0.5 cm was applied for the “Treat” function in our study.

Planning comparison

Plan comparisons were performed on the basis of the dose distribution, dose‒volume histogram (DVH), homogeneity index (HI), conformity index (CI), mean dose to NBT (D_mean), gradient index (GI), and absolute NBT volume receiving ≥12 Gy (V_12Gy), which is an important predictor of radiation necrosis (RN) in the SRS (23,24). Absolute volumes receiving ≥10% (V_10%), 25% (V_25%), 50% (V_50%), 75% (V_75%), and 100% (V_100%) of D_p were also evaluated. The CI (25) was defined as the ratio of D_p volume to the _total volume of the PTV. The HI (25) was defined as HI=D_max/D_p, where D_max is the maximum point dose to PTV_total. The GI (26) was defined as the ratio of V_50% to V_100%.

The delivery accuracy was evaluated via SRS MapCHECK^TM in combination with the StereoPHAN^TM phantom (Sun Nuclear Corporation, Melbourne, FL, USA), which has been validated to meet the quality assurance criteria specified in the AAPM Task Group 101 report (27). The gamma passing rates (GPRs) for both the TREAT-CO-VMAT and the NC-VMAT plans were evaluated via two relatively strict criteria (2%/1 mm and 2%/2 mm) with a 10% dose threshold value. Additionally, the delivery efficiency for two types of plans was evaluated on the basis of the BOT and MUs per fraction. Note that the BOT for the NC-VMAT plan includes the time for couch rotation.

Statistics

Statistical analyses in this study were performed via the Statistical Package for Social Sciences (SPSS; version 22; Chicago, IL, USA). A Wilcoxon matched-pair signed-rank test was conducted, with P values ≤0.05 considered statistically significant.

Results

Statistically significant differences were observed between the two plan techniques, with detailed quantitative results provided in Table 2. Furthermore, Table S1 presents a case-by-case dosimetric comparison for each patient across the different planning techniques. Compared with the NC-VMAT plan, the TREAT-CO-VMAT plan demonstrated superior dose fall-off, as evidenced by its lower GI [median (range): 5.09 (4.13–6.75) vs. 8.72 (5.06–12.45), P<0.05]. However, both plans had similar median CI and HI values (Table 2).

With respect to NBT sparing, the TREAT-CO-VMAT plans significantly reduced both the mean dose [1.60 (1.12–2.42) vs. 2.92 (1.63–4.08) Gy, P=0.003] and V_12Gy [12.46 (7.05–23.09) vs. 23.18 (11.86–42.11) cm³, P=0.004]. Figure 2A presents a representative patient with four lesions, who was treated with either NC-VMAT or TREAT-CO-VMAT, as shown in Figure 2B. A 0.3 mm “Treat margin” was used for the TREAT-CO-VMAT plan (Figure 2C). Additionally, Figure 3 provides a visual comparison of the 2D dose distributions and DVH and MLC patterns for the same patient with two plan techniques, highlighting the steeper dose fall-off achieved with TREAT-CO-VMAT (blue arrows).

Figure 2 Comparison of two distinct treatment techniques for a typical patient with four intracranial lesions. (A) Anterior-posterior (left) and lateral (right) digitally reconstructed radiographs. (B) Arc arrangement of TREAT-CO-VMAT and conventional single-isocenter NC-VMAT for the same patient. Four coplanar arcs and five noncoplanar arcs were used for TREAT-CO-VMAT and NC-VMAT, respectively. (C) The “Treat margins” setting for the TREAT-CO-VMAT plan. A 0.3 cm margin was used for each arc in TREAT-CO-VMAT plan. NC-VMAT, noncoplanar volumetric modulated arc therapy; TREAT-CO-VMAT, coplanar-only volumetric modulated arc therapy combined with “Treat” function.

Figure 3 Comparison of dosimetric and subfield characteristics between two different treatment techniques for a typical patient with 4 lesions. (A) Dose distribution comparison of conventional single-isocenter NC-VMAT and TREAT-CO-VMAT. The prescription dose was 20 Gy in single fraction. The yellow line indicates the PTV contour (only partial lesions are visible here). Note that the V_50% bridges could be cut between two closely spaced lesions (blue arrows) in the TREAT-CO-VMAT plan. (B) DVH of NBT and PTV_total for TREAT-CO-VMAT and NC-VMAT. (C) Comparison of the patterns of the MLC for the same control point generated by the conventional single-isocenter NC-VMAT and TREAT-CO-VMAT plans for the same patient. Note that “island blocking” problems are more common in the NC-VMAT plan (red arrows). However, TREAT-CO-VMAT can achieve one arc for one target (white arrows), which completely eliminates the “island blocking” problem. DVH, dose-volume histogram; MLC, multileaf collimator; NBT, normal brain tissue; NC-VMAT, noncoplanar volumetric modulated arc therapy; PTV, planning target volume; TREAT-CO-VMAT, coplanar-only volumetric modulated arc therapy combined with “Treat” function.

For the dose-volume metrics, the evaluated parameters generally favoured the TREAT-CO-VMAT plans over the NC-VMAT plans, with statistically significant differences observed for median V_10%, V_25%, and V_50% only (Table 2). A comparison of the MUs and BOTs between the two plan techniques is shown in Table 2. Notably, the TREAT-CO-VMAT plans generated more MUs [median (range): 13,840 (8,014–18,809)] than did the NC-VMAT plans [median (range): 4,661 (3,131–5,862)]. Although a statistically significant difference was observed in median BOTs between the two planning techniques, the median absolute difference remained within 3.5 minutes (Table 2), and the maximum difference was 7.34 minutes (Table S1; patient 7). In terms of delivery accuracy, the median GPR for the TREAT-CO-VMAT was greater than that for the NC-VMAT (Table 2).

Discussion

In this work, we propose a novel yet very simple strategy to mitigate the “island blocking” problem encountered in coplanar-only VMAT for intracranial single-isocenter multitarget SRS, thereby enhancing plan quality. Dosimetric evaluation demonstrated that, compared with the conventional single-isocenter NC-VMAT technique, the TREAT-CO-VMAT technique achieved superior plan quality and higher delivery accuracy for patients with 2–6 BMs. To the best of our knowledge, this is the first report to systematically highlight the dosimetric advantages of TREAT-CO-VMAT over conventional NC-VMAT.

Traditionally, Linac-based SRS for multiple BMs used a multiple-isocenter approach, aligning each isocenter to a single lesion and treating them one by one—prolonging OTT in proportion to lesion count. More recently, single-isocenter, multitarget NC-VMAT has become the mainstream strategy for multi-BM SRS, with several dedicated intracranial platforms now available (28-30), such as MultipleBrainMets™ (BrainLab AG, Munich, Germany), HyperArc™ (Varian Medical System, Palo Alto, CA), and Elekta HDRS (Elekta AB, Stockholm, Sweden). These platforms commonly incorporate noncoplanar delivery techniques. Although numerous studies have demonstrated the superiority of these platforms in enhancing plan quality over traditional delivery techniques (31,32), their availability is relatively limited because of their high cost and scarce resources for noncoplanar setup verification in most cancer centers. Cone-beam CT (CBCT) has been widely adopted in radiotherapy as the gold standard for IGRT, offering highly accurate patient positioning through 3D/3D image registration. Although our previous study demonstrated the feasibility of using noncoplanar CBCT for noncoplanar setup verification (33), its availability remains limited. Furthermore, some treatment platforms, such as the Varian Halcyon linac (Varian Medical Systems, Palo Alto, CA, USA), are inherently restricted to coplanar delivery (34). To make full use of the advantages of coplanar CBCT, we focused on coplanar-only VMAT for treating multiple BMs, as both coplanar VMAT and coplanar CBCT are more widely accessible and commonly used in most cancer centers.

In intracranial single-isocenter multitarget SRS, minimizing the dose to the NBT is essential for reducing the risk of RN. Several studies have demonstrated that NBT dose is affected by multiple factors, such as arc number, construction of the objective function, jaw tracking, collimator angle configuration, and the “island blocking” phenomenon (35-37). In the present study, we investigated the feasibility of employing the “Treat” function in coplanar VMAT to effectively mitigate the “island blocking” phenomenon, thereby reducing the radiation dose to NBT. Notably, dose-volume reductions of 46.25% for V_12Gy was observed with TREAT-CO-VMAT (Table 2). The lower V_12Gy in TREAT-CO-VMAT plan is expected to reduce the risk of RN. Huang et al. (38) proposed a novel method to minimize the “island blocking” problem by personalized selection of the unequal subarc collimator angle and demonstrated that this method can significantly reduce the GI value and the dose to the NBT in the VMAT plan for multiple BMs. However, as previously noted, this approach has several limitations. For example, when ≥4 lesions are treated, manually splitting arcs and choosing an appropriate collimator angle based on the beam’s-eye view becomes difficult. In addition, the procedures for full-arc segmentation and collimator selection are relatively subjective, time-consuming, and highly operator-dependent. In our prior work, we showed that manually adjusting the primary jaw size and orientation before planning substantially mitigated the “island blocking” issue (37). Likewise, the primary jaw size and jaw angle setting in our previous method also rely heavily on the planner’s experience. Additionally, completely eliminating the “island blocking” problem for those Linacs with only one pair of jaws in the absence of noncoplanar treatment fields is nearly impossible.

Interestingly, the “Treat” function can easily resolve the “island blocking” problem even without a collimator and couch angle optimization. As expected, more “island blocking” problems (Figure 3C, red arrows) were observed in the conventional NC-VMAT plan. In contrast, no “island blocking” problem was found in the TREAT-CO-VMAT plan (Figure 3C). This difference might be attributed to the distinct optimizing modes used in different versions of the RayStation TPS. In the conventional NC-VMAT plan designed with an earlier version of the RayStation TPS (version 4.7), as shown in Figure 3C, the jaws always remained open to the outermost MLC leaf edges, which resulted in the inclusion of all the targets across the entire arc span. Consequently, more MLC leaves were engaged in dose modulation, increasing the risk of the “island blocking” phenomenon. However, TREAT-CO-VMAT can achieve a one-arc-per-target configuration (Figure 3C; white arrows), preventing the issue of two targets sharing the same pair of MLC leaves and thus avoiding the “island blocking” problem. As a result, dose-volume reductions of 41.15%, 43.30% and 45.07% for V_50%, V_25%, V_10%, respectively, were observed with TREAT-CO-VMAT (Table 2). Additionally, TREAT-CO-VMAT prevented intertarget dose bridges, even for closely neighboring targets (Figure 3A; blue arrows). Kadoya and colleagues (39) demonstrated the dosimetric advantages of HyperArc™ for SRS of multiple BMs, where a GI value of 5.31 was reported. This value is comparable to the median GI value of 5.09 observed in our study. Despite the lack of a direct dosimetric comparison with HyperArc, the small GI value indicates that TREAT-CO-VMAT is capable of generating high-quality plans for SRS in patients with multiple BMs, despite the exclusive use of coplanar arcs.

In addition to improve plan quality, shortening the OTT is crucial for enhancing patient comfort, reducing intrafractional motion, and enhancing machine utilization efficiency (40,41). With respect to delivery efficiency, we observed that the TREAT-CO-VMAT had almost 2.97 times as many MUs as the NC-VMAT plan did (Table 2). However, owing to the use of fewer leaves for dose modulation and the shorter MLC travel distance, we found that the actual dose rate in TREAT-CO-VMAT was much higher than that in the NC-VMAT plan. Consequently, TREAT-CO-VMAT had only 1.47 times the BOT of the conventional NC-VMAT plan, with an absolute difference of ≤3.5 minutes. Although the maximum difference in BOT between the two plan techniques reached 7.34 minutes (Table S1; patient 7), the increased BOT is unlikely to significantly impact the patient treatment experience, given that NC-VMAT inherently requires additional time for couch rotation and noncoplanar setup verification.

SRS delivers a higher dose in a single fraction than conventional radiotherapy does, with limited opportunity for correction, thus demanding higher delivery accuracy. Our results revealed that TREAT-CO-VMAT achieved a higher GPR, which can be attributed to two key factors. First, the reduction in the number of small/irregular MLC segments in the TREAT-CO-VMAT plans improved the dose calculation accuracy, which is consistent with the study of Wolfs et al. (42). Second, setup errors induced by couch rotation in the conventional NC-VMAT may have contributed to the difference. Sun et al. (43) evaluated the impact of setup errors on the robustness of Linac-based single-isocenter coplanar and NC-VMAT plans for multiple BMs and concluded that rotational errors have a more significant negative impact on GPR for noncoplanar plans. Our findings are consistent with those of Sun et al. (43).

Several limitations in this study should be considered. First, the number of lesions included was relatively small, with a focus only on patients with 2–6 BMs. Further research is necessary to assess the performance of TREAT-CO-VMAT in more complex scenarios, such as patients with ≥10 lesions. Considering the MUs, TREAT-CO-VMAT is not recommended for treating a greater number of BMs. Second, this study was limited to purely dosimetric analysis and did not include clinical outcomes related to LC or toxicity. The potential clinical benefits of TREAT-CO-VMAT for single-isocenter SRS in treating multiple BMs will be explored in future studies. Third, owing to constraints in the TPS and Linac equipment available at our center, a comparative analysis with dedicated single-isocenter multitarget approaches, such as HyperArc, was not feasible. Despite these limitations, it is important to emphasize that our method not only provides high plan quality but also eliminates the need for couch rotations, thereby reducing the risk of setup errors.

Conclusions

The current study clearly demonstrates that, compared with the conventional single-isocenter NC-VMAT, the TREAT-CO-VMAT provides better NBT sparing and higher delivery accuracy. Most importantly, TREAT-CO-VMAT reduces the need for noncoplanar positioning verification, and it is easy to implement. In this context, TREAT-CO-VMAT presents a promising approach for single-isocenter SRS of 2–6 BMs.

Acknowledgments

None.

Footnote

Reporting Checklist: The authors have completed the STROBE reporting checklist. Available at https://qims.amegroups.com/article/view/10.21037/qims-2025-570/rc

Data Sharing Statement: Available at https://qims.amegroups.com/article/view/10.21037/qims-2025-570/dss

Funding: This work was supported by Sichuan Science and Technology Program (No. 2024YFFK0147), Sichuan University “From 0 to 1” Innovative Research Program (grant number 2023SCUH0035), Key Research and Development Projects of the Science and Technology Department of Sichuan Province (No. 2023YFS0349) and 1·3·5 Project for Disciplines of Excellence-Clinical Research Fund, West China Hospital, Sichuan University (No. 2025HXFH036).

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://qims.amegroups.com/article/view/10.21037/qims-2025-570/coif). The authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. The study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. This study was reviewed and approved by the ethics committee of the West China Hospital (Approval number: 2019535) and individual consent for this retrospective analysis was waived.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

References

1. Habbous S, Forster K, Darling G, Jerzak K, Holloway CMB, Sahgal A, Das S. Incidence and real-world burden of brain metastases from solid tumors and hematologic malignancies in Ontario: a population-based study. Neurooncol Adv 2021;3:vdaa178.
2. Mujoomdar A, Austin JH, Malhotra R, Powell CA, Pearson GD, Shiau MC, Raftopoulos H. Clinical predictors of metastatic disease to the brain from non-small cell lung carcinoma: primary tumor size, cell type, and lymph node metastases. Radiology 2007;242:882-8.
3. Brown PD, Jaeckle K, Ballman KV, Farace E, Cerhan JH, Anderson SK, Carrero XW, Barker FG 2nd, Deming R, Burri SH, Ménard C, Chung C, Stieber VW, Pollock BE, Galanis E, Buckner JC, Asher AL. Effect of Radiosurgery Alone vs Radiosurgery With Whole Brain Radiation Therapy on Cognitive Function in Patients With 1 to 3 Brain Metastases: A Randomized Clinical Trial. JAMA 2016;316:401-9.
4. Churilla TM, Ballman KV, Brown PD, Twohy EL, Jaeckle K, Farace E, et al. Stereotactic Radiosurgery With or Without Whole-Brain Radiation Therapy for Limited Brain Metastases: A Secondary Analysis of the North Central Cancer Treatment Group N0574 (Alliance) Randomized Controlled Trial. Int J Radiat Oncol Biol Phys 2017;99:1173-8.
5. Yamamoto M, Serizawa T, Higuchi Y, Sato Y, Kawagishi J, Yamanaka K, Shuto T, Akabane A, Jokura H, Yomo S, Nagano O, Aoyama H. A Multi-institutional Prospective Observational Study of Stereotactic Radiosurgery for Patients With Multiple Brain Metastases (JLGK0901 Study Update): Irradiation-related Complications and Long-term Maintenance of Mini-Mental State Examination Scores. Int J Radiat Oncol Biol Phys 2017;99:31-40.
6. Clark GM, Popple RA, Young PE, Fiveash JB. Feasibility of single-isocenter volumetric modulated arc radiosurgery for treatment of multiple brain metastases. Int J Radiat Oncol Biol Phys 2010;76:296-302.
7. Habibi MA, Mirjnani MS, Ghazizadeh Y, Norouzi A, Minaee P, Eazi S, Atarod MH, Aliasgary A, Noroozi MZ, Hajikarimloo B, Sheehan JP. Frameless stereotactic radiosurgery for brain metastasis: a systematic review and meta-analysis. Neurosurg Rev 2024;47:423.
8. Ruggieri R, Naccarato S, Mazzola R, Ricchetti F, Corradini S, Fiorentino A, Alongi F. Linac-based VMAT radiosurgery for multiple brain lesions: comparison between a conventional multi-isocenter approach and a new dedicated mono-isocenter technique. Radiat Oncol 2018;13:38.
9. Liu H, Andrews DW, Evans JJ, Werner-Wasik M, Yu Y, Dicker AP, Shi W. Plan Quality and Treatment Efficiency for Radiosurgery to Multiple Brain Metastases: Non-Coplanar RapidArc vs. Gamma Knife. Front Oncol 2016;6:26.
10. El Shafie RA, Tonndorf-Martini E, Schmitt D, Celik A, Weber D, Lang K, König L, Höne S, Forster T, von Nettelbladt B, Adeberg S, Debus J, Rieken S, Bernhardt D. Single-Isocenter Volumetric Modulated Arc Therapy vs. CyberKnife M6 for the Stereotactic Radiosurgery of Multiple Brain Metastases. Front Oncol 2020;10:568.
11. Kang J, Ford EC, Smith K, Wong J, McNutt TR. A method for optimizing LINAC treatment geometry for volumetric modulated arc therapy of multiple brain metastases. Med Phys 2010;37:4146-54.
12. Ohira S, Sagawa T, Ueda Y, Inui S, Masaoka A, Akino Y, Mizuno H, Miyazaki M, Koizumi M, Teshima T. Effect of collimator angle on HyperArc stereotactic radiosurgery planning for single and multiple brain metastases. Med Dosim 2020;45:85-91.
13. Kim JI, Ahn BS, Choi CH, Park JM, Park SY. Optimal collimator rotation based on the outline of multiple brain targets in VMAT. Radiat Oncol 2018;13:88.
14. Battinelli C, Fredriksson A, Eriksson K. Technical Note: Collimator angle optimization for multiple brain metastases in dynamic conformal arc treatment planning. Med Phys 2021;48:5414-22.
15. Nakano H, Tanabe S, Utsunomiya S, Yamada T, Sasamoto R, Nakano T, Saito H, Takizawa T, Sakai H, Ohta A, Abe E, Kaidu M, Aoyama H. Effect of setup error in the single-isocenter technique on stereotactic radiosurgery for multiple brain metastases. J Appl Clin Med Phys 2020;21:155-65.
16. Tanaka Y, Oita M, Inomata S, Fuse T, Akino Y, Shimomura K. Impact of patient positioning uncertainty in noncoplanar intracranial stereotactic radiotherapy. J Appl Clin Med Phys 2020;21:89-97.
17. Eder MM, Reiner M, Heinz C, Garny S, Freislederer P, Landry G, Niyazi M, Belka C, Riboldi M. Single-isocenter stereotactic radiosurgery for multiple brain metastases: Impact of patient misalignments on target coverage in non-coplanar treatments. Z Med Phys 2022;32:296-311.
18. Hoisak JDP, Pawlicki T. The Role of Optical Surface Imaging Systems in Radiation Therapy. Semin Radiat Oncol 2018;28:185-93.
19. Swinnen ACC, Öllers MC, Loon Ong C, Verhaegen F. The potential of an optical surface tracking system in non-coplanar single isocenter treatments of multiple brain metastases. J Appl Clin Med Phys 2020;21:63-72.
20. Covington EL, Fiveash JB, Wu X, Brezovich I, Willey CD, Riley K, Popple RA. Optical surface guidance for submillimeter monitoring of patient position during frameless stereotactic radiotherapy. J Appl Clin Med Phys 2019;20:91-8.
21. Liu S, Lai J. Zhou l, Mao E, Zhou J, Huang Y, Liu D, ZHONG R. Evaluation of the accuracy of optical surface imaging system in non-coplanar radiotherapy using orthogonal kV/MV images. Chinese Journal of Radiation Oncology 2024;33:40-48.
22. Liu S, Chen H, Lai J, Mao E, Zhou J, Huang Y, Liu D. ZHONG R. Evaluation of technical performance of stereotactic radiosurgery algorithm in optical surface imaging system in non-coplanar radiotherapy. Chinese Journal of Radiation Oncology 2023;32:438-44.
23. Korytko T, Radivoyevitch T, Colussi V, Wessels BW, Pillai K, Maciunas RJ, Einstein DB. 12 Gy gamma knife radiosurgical volume is a predictor for radiation necrosis in non-AVM intracranial tumors. Int J Radiat Oncol Biol Phys 2006;64:419-24.
24. Milano MT, Grimm J, Niemierko A, Soltys SG, Moiseenko V, Redmond KJ, Yorke E, Sahgal A, Xue J, Mahadevan A, Muacevic A, Marks LB, Kleinberg LR. Single- and Multifraction Stereotactic Radiosurgery Dose/Volume Tolerances of the Brain. Int J Radiat Oncol Biol Phys 2021;110:68-86.
25. Shaw E, Kline R, Gillin M, Souhami L, Hirschfeld A, Dinapoli R, Martin LRadiation Therapy Oncology Group. radiosurgery quality assurance guidelines. Int J Radiat Oncol Biol Phys 1993;27:1231-9.
26. Paddick I, Lippitz B. A simple dose gradient measurement tool to complement the conformity index. J Neurosurg 2006;105:194-201.
27. Benedict SH, Yenice KM, Followill D, Galvin JM, Hinson W, Kavanagh B, et al. Stereotactic body radiation therapy: the report of AAPM Task Group 101. Med Phys 2010;37:4078-101.
28. Lai J, Li A, Liu J, Zhou L. Comprehensively evaluating the performance of Elekta high-definition dynamic radiosurgery for hypofractionated stereotactic radiotherapy of multiple brain metastases. Journal of Radiation Research and Applied Sciences 2024;17:100942.
29. Huang Y, Chin K, Robbins JR, Kim J, Li H, Amro H, Chetty IJ, Gordon J, Ryu S. Radiosurgery of multiple brain metastases with single-isocenter dynamic conformal arcs (SIDCA). Radiother Oncol 2014;112:128-32.
30. Ohira S, Ueda Y, Akino Y, Hashimoto M, Masaoka A, Hirata T, Miyazaki M, Koizumi M, Teshima T. HyperArc VMAT planning for single and multiple brain metastases stereotactic radiosurgery: a new treatment planning approach. Radiat Oncol 2018;13:13.
31. Guinement L, Salleron J, Buchheit I, Gérard K, Faivre JC, Royer P, Marchesi V. Comparison between the HyperArc™ technique and the CyberKnife® technique for stereotactic treatment of brain metastases. Cancer Radiother 2023;27:136-44.
32. Jung H, Yoon J, Dona Lemus O, Tanny S, Zhou Y, Milano M, Usuki K, Hardy S, Zheng D. Dosimetric evaluation of LINAC-based single-isocenter multi-target multi-fraction stereotactic radiosurgery with more than 20 targets: comparing MME, HyperArc, and RapidArc. Radiat Oncol 2024;19:19.
33. Lai JL, Liu SP, Liu J, Li XK, Chen J, Jia YM, Lei KJ, Zhou L. Clinical Feasibility of Using Single-isocentre Non-coplanar Volumetric Modulated Arc Therapy Combined with Non-coplanar Cone Beam Computed Tomography in Hypofractionated Stereotactic Radiotherapy for Five or Fewer Multiple Intracranial Metastases. Clin Oncol (R Coll Radiol) 2023;35:408-16.
34. Sakai Y, Kubo K, Monzen H, Ueda Y, Tanooka M, Miyazaki M, Ishii K, Kawamorita R. Exploring feasibility criteria for stereotactic radiosurgical treatment of multiple brain metastases using five linac machines. J Appl Clin Med Phys 2024;25:e14413.
35. Pudsey LMM, Cutajar D, Wallace A, Saba A, Schmidt L, Bece A, Clark C, Yamada Y, Biasi G, Rosenfeld A, Poder J. The use of collimator angle optimization and jaw tracking for VMAT-based single-isocenter multiple-target stereotactic radiosurgery for up to six targets in the Varian Eclipse treatment planning system. J Appl Clin Med Phys 2021;22:171-82.
36. Yuan Y, Thomas EM, Clark GA, Markert JM, Fiveash JB, Popple RA. Evaluation of multiple factors affecting normal brain dose in single-isocenter multiple target radiosurgery. J Radiosurg SBRT 2018;5:131-44.
37. Lai J, Liu J, Zhao J, Li A, Liu S, Deng Z, Tan Q, Wang H, Jia Y, Lei K, Zhou L. Effective method to reduce the normal brain dose in single-isocenter hypofractionated stereotactic radiotherapy for multiple brain metastases. Strahlenther Onkol 2021;197:592-600.
38. Huang SX, Yang SH, Zeng B, Li XH. Personalized selection of unequal sub-arc collimator angles in VMAT for multiple brain metastases. Appl Radiat Isot 2024;214:111513.
39. Kadoya N, Abe Y, Kajikawa T, Ito K, Yamamoto T, Umezawa R, Chiba T, Katsuta Y, Takayama Y, Kato T, Kikuchi Y, Jingu K. Automated noncoplanar treatment planning strategy in stereotactic radiosurgery of multiple cranial metastases: HyperArc and CyberKnife dose distributions. Med Dosim 2019;44:394-400.
40. Wang CW, Lin YC, Tseng HM, Xiao F, Chen CM, Cheng WL, Lu SH, Lan KH, Chen WY, Liang HK, Kuo SH. Prolonged treatment time deteriorates positioning accuracy for stereotactic radiosurgery. PLoS One 2015;10:e0123359.
41. Mangesius J, Seppi T, Weigel R, Arnold CR, Vasiljevic D, Goebel G, Lukas P, Ganswindt U, Nevinny-Stickel M. Intrafractional 6D head movement increases with time of mask fixation during stereotactic intracranial RT-sessions. Radiat Oncol 2019;14:231.
42. Wolfs CJA, Swinnen ACC, Nijsten SMJJG, Verhaegen F. Should dose from small fields be limited for dose verification procedures?: uncertainty versus small field dose in VMAT treatments. Phys Med Biol 2018;63:20NT01.
43. Sun X, Guan F, Yun Q, Jennings M, Biggs S, Wang Z, Wang W, Zhang T, Shi M, Zhao L. Impact of setup errors on the robustness of linac-based single-isocenter coplanar and non-coplanar VMAT plans for multiple brain metastases. J Appl Clin Med Phys 2024;25:e14317.