Early experience with the Gamma Knife (GK) Icon — a novel form of frameless stereotactic radiosurgery (SRS) — may represent a significant advance in brain cancer surgery for patients and surgeons alike.
The US Food and Drug Administration (FDA) approved the GK Icon in 2015. This noninvasive invasive approach to GK radiosurgery (GKRS) does not require attaching a rigid frame to the patient’s head with scalp screws in order to immobilize it.
Researchers at Columbia University Irving Medical Center in New York City shared their experience on the first 100 patients treated at the institution with the frameless radiosurgical modality. They found the device to be safe and effective while improving surgeons’ workflow and allowing more patients to be treated.
“This new Icon device is the first Gamma Knife that doesn’t require the patient to be put in the Leksell G Frame,” senior author Michael B. Sisti, MD, told Medscape Medical News. “Instead, it uses a [noninvasive] plastic mask that is accurate to 0.5 mm, which is exactly the same as with the frame.
“But from a patient’s point of view, this is miracle stuff. You can have your scan done any time. It also allows us to do our planning when the patient is not even here, which vastly improves the patient experience and the doctors’ workflow,” said Sisti.
The study was published online August 2 in Neurosurgery.
From a patient’s point of view, this is miracle stuff. You can have your scan done any time. It also allows us to do our planning when the patient is not even here, which vastly improves the patient experience and the doctors’ workflow.
Cobalt-60 SRS was developed by Swedish neurosurgeon Lars Leksell in the 1960s. Although the technique allows neurosurgeons to deliver focused radiation treatment to the brain with high precision, it requires concomitant use of the rigid stereotactic frame to immobilize the patient’s head.
The frame is fixed with pins onto the patient’s skull to prevent movement during treatment and defines the stereotactic space so gamma rays accurately hit the intended target.
Yet despite its vast popularity and efficacy, immobilization with the Leksell G Frame has several drawbacks, the researchers note. The pins can be uncomfortable and sometimes cause complications, including infection and persistent pain at the insertion site.
What’s more, the invasive nature of the frame largely precludes surgeons from performing multisession fractionated radiosurgery.
The new GK Icon device dispenses with the need for a fixed frame. It incorporates an onboard conebeam computed tomography (CBCT) scanner and an infrared intrafraction motion management system.
These additions facilitate the use of a thermoplastic mask to achieve immobilization, which permits imaging and planning to be performed in advance and streamlines treatments. The mask also lends itself to multisession fractionated radiosurgery.
Despite these advances, there are very limited data available on patients treated with frameless GKSR, the authors note.
“The Gamma Knife community is very locked into the 50 years of incredible work that has been done with the Leksell G Frame,” said Sisti. “And it’s hard to beat those results. But now we have something new that may improve both the patient and physician experience.
“So somebody has to go in first, collect the data, and share their experience, and that’s what we’re doing here. In this paper we’re reporting on the first 100 patients we treated,” he said.
The case series included the first 100 patients treated at the institution with the frameless modality between April 2017 and February 2018.
Participants were selected for GKRS after consultation with a multidisciplinary team. In most cases, patients were offered the frameless option with some exceptions, including:
< 1 cm metastases and/or metastases in eloquent areas such as the brainstem or motor/sensory cortex.
Treatments that require prescription doses > 21 Gy.
Patients who cannot reliably stay still in a thermoplastic mask after a thorough assessment by the physician.
The clinicians also considered a variety of patients for fractionated (3-5 fractions) GKSR. These include individuals with large brain metastases or cavities > 2.5-3 cm, vestibular schwannomas near the cochlea, and previously irradiated patients with recurrent gliomas.
Imaging for planning the frameless technique is performed with MRI using 1-mm, thin-slice, volumetric, axial images acquired down to the C3 vertebral body. The images are imported into planning software and the scalp border is defined.
The frameless technique uses a thermoplastic mask, which is warmed and then molded over the patient’s face. Once patients are immobilized, the CBCT arm is lowered into position and a reference CBCT performed to define the baseline stereotactic space.
This reference CBCT is then incorporated into planning software, after which the dose distribution is recalculated and plan modifications made, if necessary. A second CBCT allows for pretreatment localization. After the new adapted 3D distribution and dose-volume histograms are reviewed and approved, treatment is delivered.
Although patients require only one CBCT for localization in subsequent multifraction treatments, mask shrinkage occasionally occurs, necessitating the creation of a new one, the researchers note. Such cases typically require a new reference CBCT and pretreatment localization CBCT.
During treatment, patients are assessed every day by both the radiation oncologist and specialized nurses. They receive a telephone call one day after treatment to assess potential side effects. Patients undergo regular post-treatment physical examination and diagnostic imaging according to individualized circumstances.
The median age of patients included in the series was 67 years; 19 had received prior stereotactic radiosurgery. The most common primary malignancy for metastases was nonsmall cell lung cancer (n = 18 patients; 43%), followed by breast cancer (n = 5; 12%) and melanoma (n = 3; 7%). The most common nonmetastatic lesions included meningiomas (n = 26), vestibular schwannomas (n = 16), and high-grade gliomas (n = 9).
Exactly 50% of the patients were treated in a single fraction, 19% in three daily fractions, and 31% in five daily fractions. The median treatment time was 17.7 minutes (range, 5.8-61.7 minutes). A total of 13 patients underwent repeat GKRS to treat a total of 14 lesions.
Investigators were encouraged to find that initial shifts for the first pretreatment CBCT were small, as patients remained immobilized in the thermoplastic mask.
In multifraction regimens, subsequent CBCTs had slightly greater shifts for registration in the stereotactic space. In all, 31 patients had more than one localization CBCT, including the reference scan. Common reasons for repeat CBCT included motion, patients asking for a break, or patients not tolerating the treatment position.
Fifty patients had a follow-up MRI after completing the treatment with a median follow-up of 104 days. Sixteen local recurrences were identified in nine patients with metastases and seven patients with high-grade gliomas. The crude mean time between the frameless radiosurgery and recurrence was 120 days (range, 85-314 days).
Finally, 19 patients had documented side effects that were potentially attributable to GKRS or combination surgery and postoperative GKRS. This included eight patients with grade 1 fatigue, one with grade 1 nausea, four with grade 1/2 headache, three with 1/2 seizures, one with grade 2 amnesia, two with grade 2 muscle weakness, one with grade 3 muscle weakness, one with grade 3 cerebral edema, and one with grade 4 intracranial hemorrhage and grade 4 encephalitis.
“Essentially, we’ve had no issue in any of these patients with what we consider a negative adverse event. I have followed these patients since their treatment, and nobody is having an issue,” said Sisti.
The frameless technique offers two primary advantages — improved workflow and an increased number of patients eligible for GKRS treatment because of fractionation, Sisti told Medscape Medical News.
When using the rigid Leksell G Frame, the surgical process typically starts early in the morning and is prone to unanticipated disturbances and the potential for significant delays. On the other hand, the frameless technique allows scheduling flexibility, which has improved the workflow in the GKRS suite, and increased patient convenience and comfort, he said.
“The real advantage of this from a physician’s point of view is that it allows us to do much more than we ever did before. The mask allows us to treat bigger lesions with more radiation more safely, in our opinion. So we feel it vastly expands the indications of radiosurgery,” said Sisti.
Finally, the investigators found that the frameless system increases patient comfort and safety by eliminating risks associated with the rigid frame, which include pin-site infection, scarring, numbness, and pain.
“Think of it from the patient’s standpoint. They get no preoperative testing, no medications, no sedation. They just come in and then leave. I love the Icon and think it is going to work out great. Our results have been excellent so far,” said Sisti.
“Not an Optimal Solution”
Commenting on the findings for Medscape Medical News, L. Dade Lunsford, MD, who was not involved in the study, said the frameless technology represents a “significant option” for properly selected patients.
“But in my view, it is not the optimal solution for the vast majority of patients for whom Gamma Knife radiosurgery is the appropriate tool,” said Lunsford, the Lars Leksell Professor and Distinguished Professor, Department of Neurological Surgery at the University of Pittsburgh, Pennsylvania.
“In our experience, the Icon is optimal for patients with cancer in the brain, either metastatic cancer or primary cancer, and in certain patients it does change the workflow, as Sisti and his team write in their article.”
Nevertheless, Lunsford noted that the team at Columbia has chosen to use the technology for indications with which he is not yet comfortable.
“Except in very rare cases, we do not treat skull-based tumors with multi-session radiation using Icon. The mask also has significant limitations with respect to its reliability and is poorly tolerated in many patients, especially if the patient has any concerns related to claustrophobia.
“Compared with the frame-based technique, where we can easily sedate patients, we have to be very careful about patient movement using the mask-based system,” said Lunsford.
Finally, Lunsford noted that the current study does not offer any data on outcomes after the frameless approach. “This is a nice summary, but does not define what happened to these patients after the procedure,” he said. “And what the field needs to concentrate on is not the technology, but rather long-term results. Do we improve risk while trying to make the patient more comfortable? Do we improve tumor control and response?”
Yet for Sisti, the technology has proven a boon to both provider and patient alike. “If you would have told me when I started doing this in 1988 that I’d be letting patients get on a subway and go back to work after neurosurgery, I would have laughed in your face,” he said. “But that just goes to show how technology has revolutionized everything.”
“Just like with anything in medicine, there’s going to be pushback,” Sisti added. “And you can’t argue with the great results of the Gamma Knife with the Leksell G Frame and one treatment; the results are amazing.”
Sisti and Lunsford have reported no relevant financial relationships.
Neurosurgery. Published online August 2, 2019. Full text