Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 2021;7(4):309-319.

Is there a volume threshold of brain metastases for Linac-based stereotactic radiotherapy?

Chieh-Wen Liu  1 , Saeed Ahmed  1 , Tara Gray  1 , Tianjun Ma  1 , Young-Bin Cho  1 , Gennady Neyman  1 , Samuel Chao  1 , John Suh  1 , Ping Xia  1
Affiliations

Is there a volume threshold of brain metastases for Linac-based stereotactic radiotherapy?

Chieh-Wen Liu et al. J Radiosurg SBRT. 2021.

Abstract

Purpose: To investigate whether there is a volume threshold in target volume of brain metastases below which a small cone size and sharp penumbra in Gamma Knife (GK) may provide improved plan quality when compared to Volumetric Modulated Arc Therapy (VMAT)-based stereotactic radiosurgery (SRS).

Methods: For patients treated on GK SRS for brain metastases in 2018-2019 in our institution, 121 patients with two and three targets were identified. Twenty-six patients with two or three brain metastases (total of 76 lesions) were selected for this study. Two VMAT plans, SmartArc (Pinnacle) and HyperArc (Eclipse), were generated retrospectively for each patient. Plan quality was evaluated based on RTOG conformity index (CI), Paddick gradient index (GI), normal tissue (NT) V12Gy and V4.5Gy. By using the receiver operating characteristic (ROC) curve for both VMAT plans (SmartArc and HyperArc) and metrics of RTOG CI and NT V12Gy, we compared GK plans to SmartArc and HyperArc plans separately to determine the threshold volume.

Results: For SmartArc plans, both ROC curve analyses showed a threshold volume of 0.4 cc for both CI and NT V12Gy. For HyperArc plans, the threshold volumes were 0.2 cc for the CI and 0.5 cc for NT V12Gy. GK plans produced improved dose distribution compared to VMAT for targets ≤0.4 cc, but HyperArc was found to have competing results with GK in terms of CI and NT V12Gy. For targets > 0.4 cc, both SmartArc and HyperArc showed better plan quality when compared to the GK plans.

Conclusions: Target volumes ≤0.4 cc may require a small cone size and sharp penumbra in GK while for target volumes >0.4 cc, VMAT-based SRS can provide improved overall plan quality and faster treatment delivery.

Keywords: Gamma Knife; Linac SRS; VMAT; brain metastases; plan quality; radiosurgery.

PubMed Disclaimer

Conflict of interest statement

Authors’ declaration of potential conflicts of interest Dr. Neyman reports personal fees from Elekta AB, outside the submitted work. Dr. Chao reports personal fees from Varian Medical Systems, outside the submitted work. Dr. Suh reports personal fees from Philips, other from Neutron Therapeutics, personal fees from Novocure, outside the submitted work. Dr. Xia reports grants from AVO, during the conduct of the study; grants from Philips, outside the submitted work. Other authors have nothing to disclose.

Figures

Figure 1
Figure 1
a) RTOG CI as a function of target volume for GK, SmartArc and HyperArc plans. The insert shows an enlarged view of target volumes between 0 and 1 with cut-off volumes of 0.4 cc (SmartArc) and 0.2 cc (HyperArc) using GK as a baseline. ROC curve associated with RTOG CI and a table of statistics for selected thresholds for b) SmartArc and c) HyperArc. The dots on the ROC curves correspond to the cutoff target volumes.
Figure 2
Figure 2
a) NT V12Gy as a function of target volume for GK, SmartArc and HyperArc plans. The insert shows an enlarged view of target volumes between 0 and 1 with cut-off volumes of 0.4 cc (SmartArc) and 0.5 cc (HyperArc). ROC curve associated with NT V12Gy and a table of statistics for selected thresholds for b) SmartArc and c) HyperArc. The dots on the ROC curves correspond to the cutoff target volumes.
Figure 3
Figure 3
Representative isodose distributions from GK, SmartArc and HyperArc plans for patient (#1) with two targets. Target volumes for Target 1 and Target 2 are 6.42 cc and 0.75 cc, respectively. Prescription is 13 Gy for both targets. Two-isocenter technique was used for the VMAT plans.
Figure 4
Figure 4
Representative isodose distributions of GK, SmartArc and HyperArc plans for patient (#19) with three targets. Target volumes for Target 1, Target 2 and Target 3 are 0.40 cc, 0.44 cc and 0.13 cc, respectively. Prescription was 24 Gy for all the targets. Two-isocenter technique was used for the VMAT plans, where Target 1 was associated with one isocenter and the other isocenter was placed at the geometric center of Target 2 and Target 3.
See this image and copyright information in PMC

Similar articles

See all similar articles

Cited by

References

    1. Tsao M, Xu W, Sahgal A. A meta-analysis evaluating stereotactic radiosurgery, whole-brain radiotherapy, or both for patients presenting with a limited number of brain metastases. Cancer. 2012;118(9):2486-2493. - PubMed
    1. Soliman H, Das S, Larson DA, Sahgal A. Stereotactic radiosurgery (SRS) in the modern management of patients with brain metastases. Oncotarget. 2016;7(11):12318-12330. - PMC - PubMed
    1. Mayo CS, Ding L, Addesa A, Kadish S, Fitzgerald TJ, Moser R. Initial experience with volumetric IMRT (RapidArc) for intracranial stereotactic radiosurgery. Int J Radiat Oncol Biol Phys. 2010;78(5):1457-1466. - PubMed
    1. Wolff HA, Wagner DM, Christiansen H, Hess CF, Vorwerk H. Single fraction radiosurgery using Rapid Arc for treatment of intracranial targets. Radiat Oncol (London, England). 2010;5:77. - PMC - PubMed
    1. Clark GM, Popple RA, Prendergast BM, Spencer SA, Thomas EM, Stewart JG, Guthrie BL, Markert JM, Fiveash JB. Plan quality and treatment planning technique for single isocenter cranial radiosurgery with volumetric modulated arc therapy. Pract Radiat Oncol. 2012;2(4):306-313. - PubMed

LinkOut - more resources