A method for scoring treatment time efficiency of Gamma Knife radiosurgical treatment plans for brain metastases

OBJECTIVEFor patients with multiple large brain metastases with at least 1 target volume larger than 10 cm3, multifractionated stereotactic radiosurgery (MF-SRS) has commonly been delivered with a linear accelerator (LINAC). Recent advances of Gamma Knife (GK) units with kilovolt cone-beam CT and CyberKnife (CK) units with multileaf collimators also make them attractive choices. The purpose of this study was to compare the dosimetry of MF-SRS plans deliverable on GK, CK, and LINAC and to discuss related clinical issues.METHODSTen patients with 2 or more large brain metastases who had been treated with MF-SRS on LINAC were identified. The median planning target volume was 18.31 cm3 (mean 21.31 cm3, range 3.42–49.97 cm3), and the median prescribed dose was 27.0 Gy (mean 26.7 Gy, range 21–30 Gy), administered in 3 to 5 fractions. Clinical LINAC treatment plans were generated using inverse planning with intensity modulation on a Pinnacle treatment planning system (version 9.10) for the Varian TrueBeam STx system. GK and CK planning were retrospectively performed using Leksell GammaPlan version 10.1 and Accuray Precision version 1.1.0.0 for the CK M6 system. Tumor coverage, Paddick conformity index (CI), gradient index (GI), and normal brain tissue receiving 4, 12, and 20 Gy were used to compare plan quality. Net beam-on time and approximate planning time were also collected for all cases.RESULTSPlans from all 3 modalities satisfied clinical requirements in target coverage and normal tissue sparing. The mean CI was comparable (0.79, 0.78, and 0.76) for the GK, CK, and LINAC plans. The mean GI was 3.1 for both the GK and the CK plans, whereas the mean GI of the LINAC plans was 4.1. The lower GI of the GK and CK plans would have resulted in significantly lower normal brain volumes receiving a medium or high dose. On average, GK and CK plans spared the normal brain volume receiving at least 12 Gy and 20 Gy by approximately 20% in comparison with the LINAC plans. However, the mean beam-on time of GK (∼ 64 minutes assuming a dose rate of 2.5 Gy/minute) plans was significantly longer than that of CK (∼ 31 minutes) or LINAC (∼ 4 minutes) plans.CONCLUSIONSAll 3 modalities are capable of treating multiple large brain lesions with MF-SRS. GK has the most flexible workflow and excellent dosimetry, but could be limited by the treatment time. CK has dosimetry comparable to that of GK with a consistent treatment time of approximately 30 minutes. LINAC has a much shorter treatment time, but residual rotational error could be a concern.

Download Full-text

Mask-Based versus Frame-Based Gamma Knife ICON Radiosurgery in Brain Metastases: A Prospective Randomized Trial

Stereotactic and Functional Neurosurgery ◽

10.1159/000519280 ◽

2021 ◽

pp. 1-9

Author(s):

Jean Régis ◽

Louise Merly ◽

Anne Balossier ◽

Karine Baumstarck ◽

Hussein Hamdi ◽

...

Keyword(s):

Brain Metastases ◽

Gamma Knife ◽

Treatment Time ◽

Gamma Knife Radiosurgery ◽

Nonsmall Cell Lung Cancer ◽

Pain Scale ◽

Primary Outcome Measure ◽

The Body ◽

Tumor Control ◽

Stereotactic Frame

Background: Radiosurgery is performed with a diversity of instruments relying usually either on a stereotactic frame or a mask for patient head fixation. Comfort and safety efficacy of the 2 systems have never been rigorously evaluated and compared. Material and Method: Between February 2016 and January 2017, 58 patients presenting with nonsmall cell lung cancer brain metastases have been treated by Gamma Knife radiosurgery (GKS) with random use of a frame or a mask for fixation were included patients older than 18, with <5 brain metastases (at the exclusion of brainstem and optic pathway’s locations) and no earlier history of radiotherapy. The primary outcome measure was the pain scale assessment (PSA) at the beginning of the GKS procedure. Results: The PSA at the beginning of the GKS procedure was not different between the 2 groups. The PSA at the day before GKS, before magnetic resonance imaging, just after frame application, and the day after radiosurgery (departure) has shown no difference between the 2 groups. At the end of the radiosurgery itself (just after frame or mask removal) and 1 h after, the mean pain scale was higher in patients treated with the frame (p < 0.05 and p < 0.001, respectively) but 2 patients were not able to tolerate the mask discomfort and had to be treated with frame. Tumor control and morbidity probability were demonstrated to be no difference between the 2 groups in this population of patients with BM not in highly functional area. The median of the extra dose to the body due to the cone-beam computed tomography was 7.5 mGy with a maximum of 35 mGy in patients treated with a mask fixation (null in the others treated with frame). Mask fixation was associated to longer treatment time although the beam on time was not different between the 2 groups. Conclusion: In selected patients, with brain oligo-metastases out of critical location, single-dose mask-based GKS can be done with a comfort and a safety efficacy comparable to frame-based GKS. There seems to be no clear patient data that confirm the value of the mask system with regards to comfort.

Download Full-text

A dosimetric comparison between Gamma Knife and CyberKnife treatment plans for trigeminal neuralgia

Journal of Neurosurgery ◽

10.3171/2010.8.gks101002 ◽

2010 ◽

Vol 113 (Special_Supplement) ◽

pp. 199-206 ◽

Cited By ~ 8

Author(s):

Martina Descovich ◽

Penny K. Sneed ◽

Nicholas M. Barbaro ◽

Michael W. McDermott ◽

Cynthia F. Chuang ◽

...

Keyword(s):

Trigeminal Neuralgia ◽

Gamma Knife ◽

Trigeminal Nerve ◽

Dose Distribution ◽

Treatment Time ◽

Average Length ◽

Cranial Nerves ◽

Ct Cisternography ◽

Treatment Plans ◽

Gamma Knife Perfexion

Object The Leksell Gamma Knife and the Accuray CyberKnife systems have been used in the radiosurgical treatment of trigeminal neuralgia. The 2 techniques use different delivery methods and different treatment parameters. In the past, CyberKnife treatments have been associated with an increased incidence of treatment-related complications, such as facial numbness. The goal of this study was to develop a method for planning a CyberKnife treatment for trigeminal neuralgia that would reproduce the dosimetric characteristics of a Gamma Knife plan. A comparison between Gamma Knife and CyberKnife treatment plans obtained with this method is presented. Methods Five patients treated using the Gamma Knife Perfexion Unit were selected for this study. All patients underwent CT cisternography to accurately identify the position of the trigeminal nerve. The Gamma Knife plans used either one 4-mm-diameter collimator or two coincident 4-mm collimators (one open and one with sector blocking) placed at identical isocenter coordinates. A maximum local dose of 80 Gy was prescribed. Critical structures and representative isodose lines were outlined in GammaPlan and exported to the CyberKnife treatment planning platform. CyberKnife treatments were developed using the 5-mm-diameter cone and the trigeminal node set, which provides an effective collimation diameter of 4 mm at the isocenter. The 60-Gy isodose volume imported from GammaPlan was used as the target in the CyberKnife plans. The CyberKnife treatments were optimized to achieve target dose and critical structure sparing similar to the Gamma Knife plans. Isocentric and nonisocentric delivery techniques were investigated. Treatment plans were compared in terms of dosimetric characteristics, delivery, and planning efficiency. Results CyberKnife treatments using the 5-mm cone and the trigeminal node set can closely reproduce the dose distribution of Gamma Knife plans. CyberKnife isocentric and nonisocentric plans provide comparable results. The average length of the trigeminal nerve receiving a dose of 60 Gy was 4.5, 4.5, and 4.4 mm for Gamma Knife, nonisocentric CyberKnife, and isocentric CyberKnife, respectively. However, minimizing the dose to the critical structures was more difficult with the CyberKnife and required the use of tuning structures. In addition, the dose falloff away from the target was steeper in Gamma Knife plans, probably due to the larger number of beams (192 beams for Perfexion vs ~ 100 beams for CyberKnife). While the treatment time with the CyberKnife is generally shorter, the planning time is significantly longer. Conclusions CyberKnife radiosurgical parameters can be optimized to mimic the dose distribution of Gamma Knife plans. However, Gamma Knife plans result in superior sparing of critical structures (brainstem, temporal lobe, and cranial nerves VII and VIII) and in steeper dose falloff away from the target. The clinical significance of these effects is unknown.

Download Full-text

Quantifying and improving the efficiency of Gamma Knife treatment plans for brain metastases: results of a 1-year audit

Journal of Neurosurgery ◽

10.3171/2014.7.gks141415 ◽

2014 ◽

Vol 121 (Suppl_2) ◽

pp. 44-50 ◽

Cited By ~ 2

Author(s):

Gavin Wright ◽

Paul Hatfield ◽

Carmel Loughrey ◽

Beatrice Reiner ◽

Peter Bownes

Keyword(s):

Gamma Knife ◽

Treatment Time ◽

Statistical Significance ◽

Initial Study ◽

Efficiency Index ◽

Patient Comfort ◽

Conformity Index ◽

Time Saving ◽

Planning Strategy ◽

Treatment Plans

ObjectA method for quantifying the efficiency of Gamma Knife treatment plans for metastases was previously implemented by the authors to retrospectively identify the least efficient plans and has provided insights into improved planning strategies. The aim of the current work was to ascertain whether those insights led to improved treatment plans.MethodsFollowing completion of the initial study, a 1-year audit of metastasis plans created at St. James's Institute of Oncology was carried out. Audited recent plans were compared with the earlier plans of the initial study, in terms of their efficiency and dosimetric quality. The statistical significance of any differences between relevant plan parameters was quantified by Mann-Whitney U-tests. Comparisons were made between all plans and repeated for a reduced set of plans from which the smallest lesions treated with a single 4-mm shot were excluded. The plan parameters compared were a plan efficiency index (PEI), the number of shots, Paddick conformity index (PCI), gradient index (GI), and percent coverage (of the lesion by the prescription isodose).ResultsA total of 157 metastatic lesions were included in the audit and were compared with 241 in the initial study. In a comparison of all cases, the audited plans achieved a higher median PEI score than did the earlier plans from the initial study (1.08 vs 1.02), indicating improved efficiency of the audited plans. When the smallest lesions (for which there was little scope for varying plan strategy) were discounted, the improvement in median PEI score was greater (1.23 vs 1.03, p < 0.001). This improvement in efficiency corresponds to an estimated mean (maximum) time saving of 15% (66%) per lesion (11 minutes [64 minutes] on the day of treatment). The modified planning strategy yielding these efficiency improvements did not rely on the use of significantly fewer shots (median 11 vs 11 shots, p = 0.924), nor did it result in significant detriment to dosimetric quality (median coverage 99% vs 99%, median PCI 0.84 vs 0.83, p = 0.449, and median GI 2.72 vs 2.67, p = 0.701, audited plans vs initial plans, respectively).ConclusionsChoice of planning strategy can substantially affect plan efficiency and thus strongly influence treatment time. Through increased emphasis on efficiency, resulting from the introduction of PEI combined with a modified planning strategy informed by previous work, it has been possible to reduce times for metastatic plans without compromising their dosimetric quality. Although the average time savings achieved per lesion are moderate, the potential benefits per patient are greater for those with multiple metastases. Reducing treatment times has clear benefits with regard to patient comfort and throughput. In addition, optimization of plan efficiency may potentially affect the biologically effective dose from Gamma Knife treatments and offers opportunity for further work.

Download Full-text

RADI-14. FRAMELESS STEREOTACTIC RADIOSURGERY ON THE GAMMA KNIFE ICON: EARLY EXPERIENCE FROM 42 PATIENTS WITH BRAIN METASTASES

Neuro-Oncology Advances ◽

10.1093/noajnl/vdz014.107 ◽

2019 ◽

Vol 1 (Supplement_1) ◽

pp. i24-i24

Author(s):

Horia Vulpe ◽

Akshay Save ◽

Yuanguang Xu ◽

Carl Elliston ◽

Matthew Garrett ◽

...

Keyword(s):

Brain Metastases ◽

Gamma Knife ◽

Treatment Time ◽

Cone Beam Ct ◽

Short Interval ◽

Infrared Camera ◽

Early Experience ◽

Camera System ◽

Number Of Patients

Abstract BACKGROUND: The Gamma Knife (GK) Icon uses a Cone-Beam CT (CBCT) scanner and an infrared camera system to support the delivery of frameless radiosurgery. There are limited data on patients treated with frameless GK radiosurgery (GKRS) for brain metastases. OBJECTIVE: To describe the early experience, process, technical details, and short-term outcomes with frameless GKRS for brain metastases at our institution. METHODS: We describe our patient selection and workflow for frameless GKRS in detail. Because of the short interval of follow-up, we provide crude rates of local control. RESULTS: 42 patients had a total of 96 brain metastases. Median age was 69. 77 intact lesions were treated definitively, 18 cavities postoperatively, and 1 had GKRS for recurrence after resection. 11 patients underwent repeat GKRS to the same area. Median dose was 20Gy in 1 fraction (range: 14–21), 24Gy in 3 fractions (range: 19.5–27), and 25Gy in 5 fractions (Range: 25–30). Median treatment time was 23.7 minutes (Range: 7.3 – 85.5). 29 patients had a follow-up MRI in our records after completing GKRS. Median follow-up time was 105 days (Range: 16 – 314). 16 local recurrences (LR) were identified in 9 patients. An additional 6 patients had distant brain recurrence without LR. Crude mean time between GKRS and LR was 101 days (range 44–161 days). There were 6 patients with grade 1, 3 with grade 2, 2 with grade 3, and 1 with grade 4 toxicity. We found an improvement in workflow and a greater number of patients eligible for GKRS due to the ability to fractionate treatments. CONCLUSION: We report a large cohort of consecutive patients with brain metastases treated with frameless GKRS. We look forward to studies with longer follow-up to provide valuable data on clinical outcomes and to further our understanding of the radiobiology of hypofractionation in the brain.

Download Full-text

RADI-33. DISTRIBUTED FRAMELESS GAMMA KNIFE RADIOSURGERY: A NEW TREATMENT PARADIGM FOR PATIENTS WITH BRAIN METASTASES

Neuro-Oncology Advances ◽

10.1093/noajnl/vdz014.125 ◽

2019 ◽

Vol 1 (Supplement_1) ◽

pp. i28-i28

Author(s):

Ankur Patel ◽

Jameson Mendel ◽

Aaron Plitt ◽

Lucien Nedzi ◽

Robert Timmerman ◽

...

Keyword(s):

Brain Metastases ◽

Gamma Knife ◽

Treatment Time ◽

Gamma Knife Radiosurgery ◽

Median Number ◽

Treatment Session ◽

Normal Brain ◽

Single Session ◽

Treatment Paradigm ◽

Number Of Treatment

Abstract INTRODUCTION: Stereotactic radiosurgery (SRS) has excellent efficacy for patients with limited intracranial disease. Its use in patients with >10 brain metastases remains controversial. Nonetheless, cancer patients are living longer due to advancements in systemic therapeutics and avoiding the neurocognitive toxicities of whole brain radiation therapy is critical. Recent reports suggest that SRS may be effective in patients with ≥10 metastases. Treating large numbers of brain metastases in a single Gamma Knife radiosurgery (GKRS) treatment session poses several challenges. Treatment of metastases in close proximity to one another leads to an increased dose to normal brain, potentially increasing the risk of necrosis. Furthermore, single session treatment of multiple metastases may last several hours, causing significant patient discomfort. Here, we describe a novel treatment paradigm to address these issues: distributed frameless GKRS. Patients with ≥6 brain metastases undergo multi-session frameless GKRS with both temporal and spatial distribution over 2–5 sessions, decreasing treatment time per day and not treating adjacent metastases simultaneously. METHODS: We evaluated all patients with brain metastases who underwent distributed frameless SRS, using the Gamma Knife ICON, between January 2017 and November 2018. Fifty-one patients with 1097 unique lesions were included in this analysis. RESULTS: Mean patient age was 58.8 (range 29–89) years. Median follow-up was 4.1 (range: 0–20.4) months. The median number of metastases treated was 5 (range: 1–19) per treatment session and 11.5 (range: 3–82) per treatment course. The median number of treatment sessions per treatment course was 3 (range: 2–10). The median number of treatment courses, per patient, was 1 (range: 1–4). The median margin dose was 15 Gy. The median overall survival was 5.9 (range: 0.2–20.9) months. CONCLUSIONS: Distributed frameless Gamma Knife radiosurgery is technically feasible and should be considered in lieu of single session GKRS for patients with ≥6 brain metastases.

Download Full-text

Leksell GammaPlan version 10.0 preview: performance of the new inverse treatment planning algorithm applied to Gamma Knife surgery for pituitary adenoma

Journal of Neurosurgery ◽

10.3171/2010.7.gks101033 ◽

2010 ◽

Vol 113 (Special_Supplement) ◽

pp. 144-148 ◽

Cited By ~ 9

Author(s):

David J. Schlesinger ◽

Faisal T. Sayer ◽

Chun-Po Yen ◽

Jason P. Sheehan

Keyword(s):

Treatment Planning ◽

Gamma Knife ◽

Treatment Time ◽

Gamma Knife Surgery ◽

Index Number ◽

Inverse Treatment Planning ◽

Inverse Treatment ◽

Significant Difference ◽

Treatment Plans ◽

The Mean

Object Treatment planning for Gamma Knife surgery has traditionally been a forward planning (FP)–only approach with results that depend significantly on the experience of the user. Leksell GammaPlan version 10.0, currently in beta testing, introduces a new inverse planning (IP) engine that may allow more reproducible results across dosimetrists and individual institutions. In this study the authors compared the FP and IP approaches to Gamma Knife surgery. Methods Forty-three patients with pituitary adenomas were evaluated after dose planning was performed using FP and IP treatment approaches. Treatment plans were compared for target coverage, target selectivity, Paddick gradient index, number of isocenters, optic pathways dose, and treatment time. Differences between the forward and inverse treatment plans were evaluated in a statistical fashion. Results The IP software generated a dose plan within approximately 10 minutes. The FP approach delivered the prescribed isodose to a larger treatment volume than the IP system (p < 0.001). The mean (± SD) FP and IP coverage indices were 0.85 ± 0.23 and 0.85 ± 0.13, respectively (no significant difference). The mean FP and IP gradient indices were 2.78 ± 0.20 and 3.08 ± 0.37, respectively (p < 0.001). The number of isocenters did not appreciably differ between approaches. The maximum doses directed to the optic apparatus for the FP and IP methods were 8.67 ± 1.97 Gy and 12.33 ± 5.86 Gy, respectively (p < 0.001). Conclusions The Leksell GammaPlan IP system was easy to operate and provided a reasonable, first approximation dose plan. Particularly in cases in which there are eloquent structures at risk, experience and user-based optimization will be required to achieve an acceptable Gamma Knife dose plan.

Download Full-text

Helical Tomotherapy for Brain Metastases: Dosimetric Evaluation of Treatment Plans and Early Clinical Results

Technology in Cancer Research & Treatment ◽

10.1177/153303460800700602 ◽

2008 ◽

Vol 7 (6) ◽

pp. 417-424 ◽

Cited By ~ 23

Author(s):

Natsuo Tomita ◽

Takeshi Kodaira ◽

Hiroyuki Tachibana ◽

Tatsuya Nakamura ◽

Rie Nakahara ◽

...

Keyword(s):

Brain Metastases ◽

Helical Tomotherapy ◽

Treatment Time ◽

Performance Status ◽

Invasive Technique ◽

Radiological Investigation ◽

Whole Brain ◽

Metastatic Lesions ◽

Treatment Plans

The purpose of this study was to evaluate the feasibility and treatment plans of intensity-modulated radiation therapy using helical tomotherapy (HT) for brain metastases. Twenty-three patients with 1 to 4 brain metastases were treated with H T. In combination with whole-brain radiotherapy ( simultaneous plans), metastatic lesions, and the whole brain were treated with 50 Gy and 30 Gy, respectively, in 10 fractions, with a simultaneous integrated boost technique. In patients treated for brain metastases alone ( focal plans), metastatic lesions were treated with 35 or 37.5 Gy in 5 fractions. The treatment plans were compared regarding the conformation number (CN) and homogeneity index (HI), and differences in these indexes between simultaneous and focal plans were examined by Student's t-test. Seven and 16 patients were treated with simultaneous plans and focal plans, respectively. The mean ± SD of CN and HI values were 0.75 ± 0.13 and 0.063 ± 0.042, respectively, for simultaneous plans, and 0.73 ± 0.12 and 0.052 ± 0.023, respectively, for focal plans. The CN and HI between the two plans were not significantly different. Response rates in 13 patients with follow-up imaging were approximately 90% for both plans and the local control rate at 1 year was 69%. One patient with a huge tumor (34.0 cc) and WHO performance status 3 treated with focal plans experienced severe headache, requiring prolongation of the treatment time, and died at 8 days after completion of treatment. The exact cause of deterioration was uncertain as no radiological investigation was performed in this patient. No late complications were observed during follow-up periods up to 20 months. HT is a viable non-invasive technique for treatment of brain metastases and achieves high accuracy in terms of dose conformity and homogeneity.

Download Full-text

Using Higher Isodose Lines for Gamma Knife Treatment of 1 to 3 Brain Metastases Is Safe and Effective

Neurosurgery ◽

10.1227/neu.0000000000000289 ◽

2014 ◽

Vol 74 (4) ◽

pp. 360-366 ◽

Cited By ~ 9

Author(s):

Kevin Shiue ◽

Gene H. Barnett ◽

John H. Suh ◽

Michael A. Vogelbaum ◽

Chandana A. Reddy ◽

...

Keyword(s):

Brain Metastases ◽

Gamma Knife ◽

Tumor Size ◽

Proportional Hazards ◽

Treatment Time ◽

Univariate Analysis ◽

Cox Proportional Hazards ◽

Smoking History ◽

Tumor Diameter ◽

The Impact

ABSTRACT BACKGROUND: Higher isodose lines (IDLs) in Gamma Knife (GK) Perfexion treatment of brain metastases (BMet) could result in lower local control (LC) or higher radiation necrosis (RN) rates, but reduce treatment time. OBJECTIVE: To assess the impact of the heterogeneity index (HI) and conformality index (CFI) ion local failure (LF) for patients treated with GK for 1 to 3 BMet. METHODS: From an institutional review board—approved database, 320 patients with 496 BMet were identified, treated for 1 to 3 BMet from July 2007 to April 2011 on GK Perfexion. Cox proportional hazards regression was used to analyze significance of HI, CFI, IDL, dose, tumor diameter, recursive partitioning analysis class, tumor radioresistance, primary, smoking history, metastasis location, and whole-brain radiation therapy (WBRT) history with LF and RN. RESULTS: Median follow-up by lesion was 6.8 months (range, 0-49.6). The series median survival was 14.2 months. Per RECIST, 9.5% of lesions failed, 33.9% were stable, 38.3% partially responded, 17.1% responded completely, and 1.2% could not be assessed. The 12-month LC rate was 87.3%. On univariate analysis, a dose less than 20 Gy (hazard ratio [HR]: 2.940, P < .001); tumor size (HR: 1.674, P < .001); and cerebellum/brainstem location vs other (HR: 1.891, P = .043) were significant for LF. Non-small cell lung cancer (HR: 0.333, P = .0097) was associated with better LC. On multivariate analysis, tumor size (HR: 1.696, P < .001) and cerebellum/brainstem location vs other (HR: 1.959, P = .033) remained significant for LF. Variables not significant for LF included CI, IDL, and HI. CONCLUSION: Our study of patients with 1 to 3 BMet treated with GK demonstrated no difference in LC or RN with varying HI, indicating that physicians can treat to IDL at 70% or higher IDL to reduce treatment time without increased LF or RN.

Download Full-text

Normal Brain Sparing With Increasing Number of Beams and Isocenters in Volumetric-Modulated Arc Beam Radiosurgery of Multiple Brain Metastases

Technology in Cancer Research & Treatment ◽

10.1177/1533034615614208 ◽

2016 ◽

Vol 15 (6) ◽

pp. 766-771 ◽

Cited By ~ 8

Author(s):

Sabbir Hossain ◽

Vance Keeling ◽

Kimberly Hildebrand ◽

Salahuddin Ahmad ◽

David A. Larson ◽

...

Keyword(s):

Brain Metastases ◽

Brain Tissue ◽

Gamma Knife ◽

Normal Brain ◽

Normal Brain Tissue ◽

Benchmark Study ◽

Multiple Brain Metastases ◽

Study Results ◽

Treatment Plans ◽

Volumetric Modulated Arc Radiotherapy

Recent studies have reported about the application of volumetric-modulated arc radiotherapy in the treatment of multiple brain metastases. One of the key concerns for these radiosurgical treatments lies in the integral dose within the normal brain tissue, as it has been shown to increase with increasing number of brain tumors treated. In this study, we investigate the potential to improve normal brain tissue sparing specific to volumetric-modulated arc radiotherapy by increasing the number of isocenters and arc beams. Adopting a multi-institutional benchmark study protocol of planning multiple brain metastases via a radiosurgical apparatus, a flattening filter-free TrueBeam RapidArc delivery system (Varian Oncology, Palo Alto, California) was used for a volumetric-modulated arc radiotherapy treatment planning study, where treatment plans for target combinations of N = 1, 3, 6, 9, and 12 targets were developed with increasing numbers of isocenters and arc beams. The treatment plans for each target combination were compared dosimetrically among each other and against the reference Gamma Knife treatment plan from the original benchmark study. We observed that as the number of isocenters or arc beams increased, the normal brain isodose volumes such as 12- to 4-Gy on average decreased by up to 15% for all the studied cases. However, when the best volumetric-modulated arc radiotherapy normal brain isodose volumes were compared against the corresponding reference Gamma Knife values, volumetric-modulated arc radiotherapy remained 100% to 200% higher than those of Gamma Knife for all target combinations. The study results, particularly for the solitary (N = 1) metastases case, directly challenged the general notion of dose equivalence among current radiosurgical modalities. In conclusion, multiple isocenter and multiple arc beam delivery solutions are capable of decreasing normal brain irradiation exposure for volumetric-modulated arc radiotherapy. However, there is further technological development in need for volumetric-modulated arc radiotherapy before similar dosimetric treatment plans could be achievable when compared to Gamma Knife radiosurgery.

Download Full-text