Tolerability and Stability of Mask Fixation in Gamma Knife Stereotactic Radiosurgery: Predictors of Treatment Interruptions

Main Article Content

F Yang, MD G Bowden, MD S Patel, MD S Ghosh, PhD J Yun, PhD K Aronyk, MD J Amanie, MD B Warkentin, PhD M Larocque, PhD A Heikal, PhD LS Rowe, MD BM Wheatley, MD PhD A Fairchild, MD


Background. Frameless fixation with a thermoplastic mask is an alternative to traditional frame-based immobilization for Gamma-Knife stereotactic radiosurgery (SRS) or fractionated stereotactic radiotherapy (FSRT). However, interruptions during beam-on time can significantly prolong treatment delivery, impacting patient experience and unit workflow.

Aim. We investigated clinical and technical predictors of treatment interruptions, and the phases of treatment during which interruptions are most likely to occur.

Methods. Patients undergoing frameless Gamma Knife SRS or FSRT in 2020 were retrospectively reviewed. Clinical parameters were extracted from electronic medical records. Dosimetric and treatment interruption data were obtained from Gamma Knife treatment reports. Univariate and multivariate analyses analyzed technical and clinical predictors of treatment interruptions.

Results. Our cohort included 84 patients receiving 141 fractions encompassing 255 lesions. 49/84 (58.3%) were female, 79/84 (94.0%) had brain metastases, 49/84 (58.3%) were taking dexamethasone and 30/84 (35.7%) used analgesics. 89/106 (84.0%) courses were single fractions. Mean planned beam-on time was 37.1 minutes (range 7.1-118.8 min) versus a total bed time of 64.9 minutes (range 15-252min) per fraction. 64.5% (91/141) of fractions were interrupted at least once; 12/141 fractions were paused 20 times or more, with a maximum 54 pauses. The mean number of pauses per quartile decreased the further the patient proceeded in beam-on time, and patients receiving first lifetime cranial radiation paused more often than during subsequent fractions. At least one pause occurred in 100% of fractions with a planned beam-on time exceeding 60 minutes. Planned beam-on time, number of gating events and high-definition motion management alarms significantly correlated with total number of pauses on multivariate analysis (all p<0.0001); these three factors, along with prep time and number of operator-initiated pauses, predicted total time on the Gamma Knife couch (all p<0.0001). Clinical factors, medication use, and prior SRS/FSRT were not predictive of pauses.

Conclusions. Planned beam-on time, number of gating events and high-definition motion management alarms significantly predicted likelihood of interruptions during frameless Gamma Knife SRS/FSRT. These factors should be considered in selection of immobilization method, especially if exceeding 60 minutes.

Article Details

How to Cite
YANG, F et al. Tolerability and Stability of Mask Fixation in Gamma Knife Stereotactic Radiosurgery: Predictors of Treatment Interruptions. Medical Research Archives, [S.l.], v. 10, n. 11, nov. 2022. ISSN 2375-1924. Available at: <>. Date accessed: 25 feb. 2024. doi:
Research Articles


1. Leksell L. The stereotactic method and radiosurgery of the brain. Acta chir scand. 1951;102:316-319.
2. Vulpe H, Save A, Xu Y, et al. Frameless stereotactic radiosurgery on the Gamma Knife Icon: Early experience from 100 patients. Neurosurg. 2020;86(4):509-516.
3. Wright G, Harrold N, Hatfield P, Bownes P. Validity of the use of nose tip motion as a surrogate for intracranial motion in mask-fixated framless Gamma Knife Icon therapy. J Radiosurg SBRT. 2017;4:289-301.
4. Schlesinger D, Xu Z, Taylor F, et al. Interfraction and intrafraction performance of the Gamma Knife Extend system for patient positioning and immobilization. J neurosurg. 2012;117(Special_Suppl): 217-224.
5. Grimm M, Koppen U, Stieler F, et al. Prospective assessment of mask versus frame fixation during Gamma Knife treatment for brain metastases. Radiother Oncol. 2020;147:195-199.
6. Li W, Cashell A, Lee I, et al. Patient perspectives on frame versus mask immobilization for gamma knife stereotactic radiosurgery. J Med Imag Radiat Sci. 2020;51:567-573.
7. Bennion N, Malouff T, Verma V, et al. A comparison of clinical and radiologic outcomes between frame-based and frameless stereotactic radiosurgery for brain metastases. Pract rad onc. 2016;6:e283-e290.
8. Ramakrishna N, Rosca F, Friesen S et al. A clinical comparison of patient setup and intra-fraction motion using frame-based radiosurgery versus a frameless image-guided radiosurgery system for intracranial lesions. Radiother Oncol. 2010;95:109-115.
9. Arino C, Stadelmaier N, Dupin C, et al. Le masque de contention en radiotherapie: Une source d’anxiete pour le patient? Cancer Radiother. 2014;18:753-756.
10. Foote R, Pollock B, Link M et al. Leksell Gamma Knife coordinate setting slippage: How often, how much? J Neurosurg. 2004;101:590-593.
11. Lunsford LD, Niranjan A, Fallon K, Kim J. Frame versus frameless Leksell stereotactic radiosurgery. Leksell Radiosurgery, Niranjan A, Lunsford LD, Kano H (Eds). Prog Neurol Surg. 2019;34:19-27.
12. Ganz J. Gamma Knife evolving instrumentation. Prog Brain Res. 2022;268:49-63.
13. Dutta S, Kowalchuk R, Trifiletti D, et al. Stereotactic shifts during frame-based image-guided stereotactic radiosurgery: Clinical measurements. Int J Radiat Oncol Biol Phys. 2018;102(4):895-902.
14. Duggar W, Morris B, Hu R, Yang C. Predictors of significant patient movement during frameless radiosurgery with the Gamma Knife® Icon™ cone-beam CT. Cureus. 2022;14(1):e21380.
15. Li W, Bootsma G, Von Schultz O, et al. Preliminary evaluation of a novel thermoplastic mask system with intra-fraction motion monitoring for future use with image-guided Gamma Knife. Cureus. 2016;8(3):e531.
16. Regis J, Merely L, Balossier A, et al. Mask-based versus frame-based Gamma Knife Icon radiosurgery in brain metastases: A prospective randomized trial. Stereotact Funct Neurosurg. 2022;100:86-94.
17. MacDonald R, Lee Y, Schasfoort J, et al. Real-time infrared motion tracking analysis for patients treated with gated frameless image guided stereotactic radiosurgery. Int J Radiat Oncol Biol Phys. 2020;106(2):413-421.
18. Wegner R, et al. Predictors of treatment interruption during frameless gamma knife icon stereotactic radiosurgery. Adv Radiat Onc. 2020;5:1152-1157.
19. Pavlica M, Dawley T, Goenka A, Schulder M. Frame-based and mask-based stereotactic radiosurgery: The patient experience, compared. Stereotact Funct Neurosurg. 2021;99:241-249.
20. Bush A, Vallow L, Ruiz-Garcia H, et al. Mask-based immobilization in Gamma Knife stereotactic radiosurgery. J Clin Neurosci. 2021;83:37-42.
21. Mendel J, Schroeder S, Plitt A, et al. Expanded radiosurgery capabilities utilizing Gamma Knife Icon. Cureus. 2021;13(3):e13998.
22. Seneviratne D, Vallow L, Hadley A, et al. Intracranial motion during frameless Gamma-Knife stereotactic radiosurgery. J Radiosurg SBRT. 2020;6(4):277.
23. Carminucci A, Nie K, Weiner J, et al. Assessment of motion error for frame-based and noninvasive mask-based fixation using the Leksell Gamma Knife Icon radiosurgery system. J neurosurg. 2018;129(Suppl1):133-139.
24. Wegner R, Horne Z, Xu L, et al. Adaptation of a Gamma Knife Icon stereotactic radiosurgery program in the face of the COVID-19 pandemic. J Radiosurg SBRT. 2020;7:5-10.
25. MacDonald R, Lee Y, Schasfoort J, et al. Technical note: Personalized treatment gating thresholds in frameless stereotactic radiosurgery using predictions of dosimetric fidelity and treatment interruption. Med Phys. 2021;48:8045-8051.
26. Mangesius J, Seppi T, Weigel R, et al. Intrafractional 6D head movement increases with time of mask fixation during stereotactic intracranial RT sessions. Radiat Oncol. 2019;14:231.