Apr 12, 2017
The addition of Icon allows an increased number of patients to receive intracranial SRS – and an increase of indications treated
Appreciating that Leksell Gamma Knife® Icon™ represents the quintessential platform for performing intracranial stereotactic radiosurgery (SRS), clinicians at Universitätsmedizin Mannheim (UMM) set about in 2014 to incorporate the technology into their well-equipped radiation therapy department.
SRS, a stable treatment technique at UMM since 2001, had been delivered exclusively via linear accelerator for all intracranial cases – about 50 patients per year. In 2013, UMM officials knew that Icon was on the horizon, a system that attracted them with its cone beam CT (CBCT), frame-based and frameless (via thermoplastic mask) treatment options and advanced motion management (HDMM), in addition to the well-known exceptional accuracy of Gamma Knife technology.
“Since Leksell Gamma Knife® Perfexion™ could be easily upgraded to the Icon configuration, we decided that we would first get a Perfexion system installed,” says Leading Senior Physician, Sabine Mai, MD. “Doing this would be an excellent way to establish and familiarize ourselves with the Gamma Knife workflow.”
“The Gamma Knife system delivers an extremely low extracranial dose in comparison to a linac or CyberKnife system, Dr. Mai notes. “We also obtain highly conformal plans with steep dose gradients, which is very important when high doses are being delivered close to critical structures, such as the optic nerve or chiasm.”
She adds that margins can be reduced with Gamma Knife compared to linac SRS; smaller margins mean less irradiation to healthy tissues. The use of Perfexion at UMM reinforced the center’s trend toward favoring brain SRS over whole brain radiation therapy (WBRT). Another difference has been the ability to treat many more metastases (≤10) in a single session.
Icon increases departmental efficiency
UMM RT staff were sufficiently impressed by the streamlined workflow and clinical potential of Gamma Knife technology that they decided to schedule a 2015 upgrade from Perfexion to Leksell Gamma Knife Icon. By August, the system was up and treating patients.
“Our department has a long history in IGRT and frameless SRS with linacs, so we were eager to upgrade to Icon with its image guidance, and also looking forward to the opportunity to deliver frameless treatment – while still keeping the option to use frame fixation in select cases,” says Florian Stieler, PhD, Senior Physicist. “Icon also offers other new capabilities that we did not have previously, such as adaptive dose delivery and continuous patient monitoring.”
Adaptive dose delivery, he adds, enables treatments to be adjusted according to daily patient position parameters, allowing physicians to perform fractionated treatments on Icon. For each treatment, CBCT is used to verify patient position, which is automatically matched to the reference CT or MRI scan, and the system provides translational and rotational shifts. These shifts are corrected using shot position, and the dose distribution is recalculated.
“If there is a large shift, depending on the daily situation, and the resulting dose distribution is not what we expect, then we can reposition the patient,” Dr. Stieler says. “For extra assurance, the system provides information about plan quality at the beginning and end of treatment, enabling us to see that we delivered what we planned.”
Greater flexibility equates to more patient benefits
With Icon, UMM radiation oncology department staff have a specialized tool for treating the brain that is also very flexible, according to Dr. Stieler.
“We can choose different methods for positioning – with the frame or frameless – and we can perform multiple different fractionation schemes depending on the indication and the patient’s needs.”
Having options available for patients with brain indications is critical, Dr. Mai agrees.
“For example, one patient required a frame-based treatment, but we could only fix three of the frame posts,” she recalls. “The CBCT imaging on Icon allowed us to confirm that the patient was still in the correct position, even with three posts, giving us greater confidence to proceed.”
“Alternatively, some patients may be claustrophobic in the mask,” she says. “Consequently, we might opt to treat them using the frame. Conversely, a patient may have had several craniotomies, making it difficult to fix the frame screws, so we could choose to use the mask for that patient. This flexibility is important for both patients and staff.”
“In some cases, we have been able to treat benign meningioma with five fractions of 5 Gy,” Dr. Mai adds. “We also treat patients using normal fractionation, allowing patients to benefit from the traditional advantages of Gamma Knife radiosurgery, such as low extracranial dose, conformality and high precision, even with frameless.”
Currently about two thirds of Gamma Knife Icon patients at UMM are treated using the frame and about one third in a mask.
More indications, high availability
Icon has enabled UMM staff to treat not only more patients in general, but also to treat more intracranial indications, according to Dr. Stieler.
Previously, Mannheim clinicians treated some benign conditions, such as pituitary adenoma and acoustic neuroma, using the linac. Now, however, they can treat such conditions with even smaller margins on Icon. Such targets are often located close to critical structures, so reduced margins provide safer treatments for patients.
“We can now treat virtually all patients for intracranial tumors with SRS or fractionated SRT with Icon,” he says. “This gives us more linac availability for other treatments, like SBRT, and there also is an advantage to using both modalities for certain patients.”
In 2013, approximately 50 patients were treated in the department using linac-based SRS. In the first year of having a Gamma Knife system, this number decreased to about 30 patients, while 56 patients were treated using Gamma Knife SRS. In 2016, all cases of intracranial SRS or fractionated SRT were delivered using Gamma Knife Icon, and by October 2016, 92 treatments had been performed (including individual treatment fractions in cases of fractionated SRT) – already nearly double the number of treatments performed in 2013.
“Not only have we increased the number of patients to receive intracranial SRS and fractionated SRT, but we have also increased the number of indications [malignant and benign] that we can treat,” Dr. Stieler notes. “We have also begun to treat postoperative cavities following resection of brain metastases using fractionated SRS [3 X 10 Gy every two weeks], which has contributed to the high number of treatments that we have performed in 2016.”