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

Abstract

<b><i>Background:</i></b> 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. <b><i>Material and Method:</i></b> 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. <b><i>Results:</i></b> 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 (<i>p</i> < 0.05 and <i>p</i> < 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. <b><i>Conclusion:</i></b> 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.

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

“…Treatment duration was the main factor associated with discomfort, which becomes "unbearable", according to the authors, after one hour in the mask. 16 Our results are consistent with other recent publications regarding treatment interruptions (Table 4). Bush et al treated 124 patients with 358 intracranial tumours in a mask (01/2018-12/2019).…”

“…18,21,25 While there are dosimetric methods within Gamma Plan to decrease beam-on time, it is suboptimal to accept a lower quality treatment plan in order to reduce mask-on time. 11,16 From published literature including our data, mask-based immobilization appears most likely to be tolerable when planned beam-on time is less than 60 minutes. Interestingly, in our patients with interruptions, the frequency of pauses decreased over the course of the fraction.…”

“…14 If the deviation exceeds threshold for >30 seconds continuously or occurs >5 times during delivery of the same isocentre, the couch automatically moves to the home position, and the shielding doors close. 11,16 The operator then waits until the deviation falls below threshold and irradiation can resume, or a new CBCT is required. Beam pauses and repeat CBCT scans prolong a patient's time on the GK couch and disrupt overall unit workflow.…”

“…Beam pauses and repeat CBCT scans prolong a patient's time on the GK couch and disrupt overall unit workflow. [17][18] Frameless techniques are generally more comfortable for the patient, 6,16,19 and provide more flexibility in the treatment planning process. Mask construction and treatment planning imaging can be performed in advance.…”

“…Protracted workflow related to fixation method has been recently reported in a phase III randomized trial. 16 58 NSCLC patients with <5 unresected brain metastases were randomized 1:1 between frame or frameless fixation (02/2016-01/2017). The primary endpoint was patient comfort, which was rated more highly by patients in a mask compared to the frame.…”