Cyberknife radiosurgery in modern Oncology

Radiosurgery and stereotactic radiotherapy have become firmly established as an alternative or supplement to surgery and conventional radiotherapy.




Fabian Fehlauer,

Strahlenzentrum Hamburg,




In fact, the treatment spectrum of Cyberknife radiosurgery is continuously expanding due to increasing scientific and clinical work-up by the radio-oncological societies in which the Strahlenzentrum Hamburg is integrated.





Overview of the most common cyberknife indications



Head / Brain













Spine / spinal cord












Kidney / adrenal gland


Liver / pancreas

Brain metastases (usually 1-4,> 4 in selected cases)

Acoustic neurinoma


Pituitary adenomas


Glomus tumors (paraganglioma)


Malignant glioma recurrence after pre-irradiation

Head and neck tumor recurrence after pre-irradiation


Bone metastases and intraspinal metastases




Non-small cell lung carcinoma up to stage IIA (cT1-2 N0)

Lung metastases in limited numbers


Primary prostate cancer of low to medium risk

Local recurrence of prostate cancer

Lymph node or/and bone metastases in limited numbers (oligometastasis)


Adrenal metastases

Selected cases of renal cell carcinoma


Liver metastases in limited numbers

Selected cases of hepatocellular carcinoma and pancreatic carcinoma

Overview of the most common Cyberknife indications

The term stereotactic radiosurgery was mentioned in 1951 by Lars Leksell, Professor of Neurosurgery at the Karolinska Institute (Sweden) for the Gammaknife, which was revolutionary at the time, but has many drawbacks from today’s point of view. Environmentally unfriendly cobalt-60 sources, drill holes on the patient’s skull, and significantly limited use do not exist on Cyberknife. The first robotic-assisted radiosurgery system, developed at Stanford University (USA) by neurosurgeon John Adler, was approved in 1987 in the U.S., and in 2002 in Europe for radiosurgery. Today, about 300 Cyberknife worldwide exists, mostly as a sole treatment method. The Strahlenzentrum Hamburg (founded in 2007 by Fabian Fehlauer), operates since 2011 as the first and so far only non-governmental, non-hospital radiotherapy centre in Germany with Cyberknife technology. The expertise and technical equipment in Hamburg has been consistently improved since 2007 through permanent applications, team training and new investments in state-of-the-art therapy.

Cyberknife Centre Hamburg, PD

Dr. Fehlauer and the doctors team

Thus, an outpatient radiotherapy centre, which offers all the modern techniques, is of benefit to the patients, as it is possible to apply individualized quasi-tailor-made concepts.

Cyberknife radiosurgery offers two unique capabilities with the 6-axis robot and real-time treatment of moving tumors. However, therapy planning also presupposes technical and clinical conditions, such as a clearly definable target structure, size of the lesion, delimitation to healthy tissue, as well as a sufficient general condition and cooperation of the patient.

Only with the most modern techniques of therapy and imaging, the disease can be treated with high precision, pinpoint accuracy, analogous to a “virtual knife”, without hurting sensitive and adjacent tissue.

In contrast to the several weeks of radiation therapy on the conventional linear accelerator, 100 to 300 fine bundles of photon rays are released from the Cyberknife on one day of treatment within one hour, so that the tumor tissue can be killed particularly precisely and sustainably. Thus, the tumor is treated with ultra-fine and high-energy X-rays under view control with the best possible protection of the surrounding tissue. Patients have no limitations and can go about their daily activities on the same day.

Often, only one treatment is needed to achieve high probability of maximum local tumor control with maximum patient comfort, minimal risk, and high quality of life.

Radiosurgery of the head

Brain metastases

Brain metastases in limited numbers and with a diameter of up to 3 cm are an optimal target for Cyberknife (CK). Irradiation takes place depending on size and localization in one to three sessions and can be done with different concepts (eg 1 × 21 Gy resp. 3 × 8-9 Gy) with local tumor control depending on the histology of 73-94%

The resection cavity after surgery should be treated depending on the size, in 1 to 5 applications, on the CK to improve the local control by 30%.

Treatment example Metastasis

Acoustic neurinoma

Regardless of the patient’s age and taking into account the health-related quality of life, radiosurgery at the CK is now considered as a non-invasive alternative, in particular for preserving the auditory function and the facial nerve. Radiosurgery is usually applied with 1 x 13 Gy to a success rate is 94% without any damage to the hearing function.


Cyberknife radiosurgery can be offered as a primary treatment option for smaller, difficult to remove meningioma’s or their relapses (eg, in the cavernous or optic sinus), multiple meningioma, perioperative risk, or if desired by the patient as an alternative.

Depending on the size and localization, radiosurgery was performed in one to five treatments (e.g., 1 x 15 Gy, 5 x 5 Gy) with excellent progression-free interval (3.5.8 years, 110%, 93%, 90%).

Treatment example Meningioma

Arteriovenous malformations

Congenital vascular malformation is a common cause of intracerebral haemorrhaging in younger patients. The interdisciplinary therapy decision is an individual risk assessment between bleeding and therapeutic morbidity. Radiosurgery reduces the risk of bleeding in the long-term due to closure of the vessels (5, 10 years, 70%, 85%).

Brain tumors

In the recurrence therapy of glioblastoma, there are increasing reports that re-irradiation by CK radiosurgery is feasible with low toxicity and can delay the natural progression – analogous to conventional re-irradiation – for further months. Thus, the already limited lifetime is not filled with further visits to the clinic and the doctor.


Radiosurgery of the body

Lung carcinomas

With regard to relapse (86% vs. 80%) and survival (95% vs. 79%), radiosurgery with Cyberknife is superior to surgery (phase III, F/U 3 years), although the quality of life is certainly better but does not capture the study endpoint has been. According to the NCCN recommendation in early-stage NSCLC (to IIA), for older patients (> 75 years of age), patients with potential lung-lobe loss from surgery or patients with inadequate pulmonary function or multi-morbidity, radiosurgery (or stereotactic radiation) is considered the “gold standard”.

Prostate cancer

There is sufficient data to recommend Cyberknife as an extremely effective and low-side-effect option for patients with low and moderate risk carcinoma profiles. After 5 applications (e.g., 5 x 7.25 Gy), only minor and short-term irritation symptoms without significant late toxicity (<2% urogenital) with a 5-year relapse-freedom of 97% were documented. Despite a lack of long-term follow-up data (> 10 years), according other (historical) radiation therapy (HDR / LDR brachytherapy), is not expected to have an unfavourable long-term course, given higher biological effectiveness and high conformal physical dose distribution.

Meanwhile there are also first good experiences and results with the Cyberknife in recurrences after conventional large field irradiation.

Treatment Example Prostate

Renal cell carcinoma

If a patient is ineligible for surgery or rejects it, Cyberknife should be included as a possible alternative in the oncological discussion.

Metastases, oligometastases

Cyberknife is most commonly used in lung, liver, adrenals, bone and lymph node metastases (e.g., 1 x 18 Gy, 3 x 15 Gy, 6 x 7 Gy). The number of applications depends on organ, organ involvement, localization, size and desired biological effectiveness. Radiosurgery achieves high control rates in the course of palliative management (up to 90%) and can also be applied simultaneously to some systemic therapies.

For patients with one or a small number of metastases (oligometastases), there are first indications that progression-free survival can be prolonged by radiosurgery or that the time of systemic therapies with their side effects can be delayed.

Spinal and intramedullary metastastases

If a metastasis can be clearly delineated in thin-slice MRI in an affected vertebral body or even intraspinally localisation, a single radiosurgery treatment can be considered (eg. 1 x 18 Gy). Cyberknife is also used successfully in radiotherapy pre-treated but progressive metastases or parallel to conventional radiotherapy of a metastatic vertebral body to intensify the biological effectiveness (“boost”).


Cyberknife as an innovative radiosurgery is now an established, non-invasive radio-oncological therapy option with a wide range of indications and increasing evidence, which should be offered to patients in the context of interdisciplinary treatment.


Literature by personal request


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Karl Storz
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Karl Storz