Cyberknife

Stereotactic body radiotherapy (SBRT) with the Cyberknife

Conventional radiotherapies of the prostate are characterised by repeated irradiations, each with a low dose, because the radiation cannot be sufficiently focused on the prostate. Thus, the surrounding tissue, especially the intestine and the urinary bladder, is also damaged by the radiation. To keep side effects low, the total dose is divided into up to 45 “fractions”. This means that the patient needs up to 45 radiotherapy appointments, with daily therapy sessions for a total of up to 9 weeks.


Unlike many other cancers, however, prostate cancer responds particularly well to a few high-dose irradiations. Due to the much better focus on the prostate, SBRT with the Cyberknife allows the total dose to be applied in only 5 sessions – with less damage to the surrounding organs. Each session lasts about 15 to 30 minutes.

The illustration shows the so-called isodose course around the prostate during cybernife irradiation: The isodoses (concentric contours in different colours) run very close together. It shows a rapid decrease in the radiation dose around the prostate. Rectum (blue) and bladder (orange) are only partially hit and with low radiation doses. The prostate receives the maximum dose (yellow contour). This minimises side effects and maintains the patients’ quality of life.


In this way, cybernife irradiation has in the meantime surpassed even proton therapy in terms of precision.

Robot-guided radiation source delivers sharp dose gradients

The Cyberknife differs from radiation therapy systems in that a conventional radiation source (high-energy photons) is attached to an industrial robot system, and thus freely movable in space. This allows a tumour in the patient’s body to be irradiated from all spatial directions with a sharply focused beam (“pencil beam”).

The CyberKnife’s robotic system thereby seamlessly delivers non-coplanar, non-isocentric and isocentric beams from a variety of angles. These unique delivery options generate conformal dose distributions and enable precise and effective treatments.

Of particular importance are the sharp dose gradients that are typical of the cyberknife. Because ideally, the tumour should be hit with maximum radiation dose, and the surrounding tissue with a dose of zero. Of course, this ideal dose distribution can never be achieved. But dropping as quickly as possible from the maximum dose in the tumour (e.g. 80 grays) to very low doses of 2-5 grays within a transition zone only 1 – 2 cm wide minimises the radiation dose to surrounding organs such as the bladder, rectum and nerves and vessels.

Cyberknife (SBRT) irradiation procedure

SBRT consists of a much shorter course of radiation than conventional approaches, with only five treatment sessions. This is achieved by administering a higher dose per day, which requires considerable precision and accuracy, drawing on the expertise of the treating radiation oncologist and a team of medical physicists, medical dosimetrists and radiotherapists. Modern and advanced linear accelerator technology is also required. A total of six visits to the department are required for the planning and implementation of SBRT (one planning visit and five treatment visits).

Advantages of Cyberknife (SRBT) irradiation

There are many good reasons to consider cyberknife radiation (SBRT). Advantages over conventional radiotherapy include:

Synchronisation of movement in real time

The revolutionary Synchrony® system uses artificial intelligence to adapt the treatment to the movements of the patient and/or target in real time without human intervention. At the touch of a button, CyberKnife S7™ treatments can be performed continuously, efficiently and without interrupting standard workflows.

Disadvantages of radiotherapy

Im Allgemeinen ist jedoch die Strahlentherapie, unabhängig von der verwendeten Technik (iMRI = intensitätsmodulierte Strahlentherapie, PT, CN usw.), nicht die beste Wahl als Erstlinientherapie. This is because radiation therapy leaves genetic damage to the tissues that are in the marginal area of radiation. This results in chronic inflammation and severe scarring, especially in the area of the bladder and rectum when prostate cancer is irradiated. This chronic damage also reduces the ability of tissues to heal wounds, making further treatments in the radiation field much more difficult. Thus, further irradiations are usually not possible at all. The so-called “salvage” prostatectomy (rescue prostatectomy) is only performed by a few experts and results in pronounced incontinence in almost all cases. Since radiation therapies do not require anesthesia, they should be used primarily in old and sick men for whom anesthesia is too much of a burden.

The side effects of radiotherapy are comparable to those of radical prostatectomy, although the incontinence rate is slightly lower with RT than with RPE, but the disruption of bladder and bowel function is higher1.

NanoKnife treatment

The gentle alternative to radiotherapy

These side effects can be almost completely avoided by a new treatment method for prostate cancer that no longer uses ionising radiation, but ultra-short, strong electrical pulses, the so-called “Irreversible Electroporation (IRE)“, which was developed to application maturity at the VITUS Prostate Centre.

Long-term consequences
2 years
5 years
15 years
Incontinence
RPE
RT
9,6%
3,2%
13,4%
4,4%
18,3%
9,4%
Impotence
RPE
RT
78,8%
60,8%
75,7%
71,9%
87,0%
93,9%
Disturbance of the
Intestinal function
RPE
RT
13,6%
34,0%
16,3%
31,3%
21,9%
35,8%

Table: Long-term consequences of radical prostatectomy (RPE) and radiotherapy (RT) for prostate cancer regarding incontinence, impotence, and impaired bowel function. Translated into German by Resnik MJ, Koyoma T, Fan K-H, et al. N Engl J Med 2013; 368:436-45.

References
  1. Resnik MJ, Koyoma T, Fan K-H, et al. N Engl J Med 2013; 368:436-45.