What conditions can be treated?
Arteriovenous malformations, other vascular anomalies (cavernoma, haemangioblastoma, glomus tumour), meningiomas and acoustic neuromas are now (in many cases) preferentially treated by stereotactic radiosurgical techniques such as CyberKnife. The vascular anomalies slowly obliterate whilst the meningiomas and neuromas tend to stay as ‘tomb stones’ on scanning but not to re-grow. The success of radiosurgery has made orthodox surgery obsolete for many patients and the risks of orthodox surgery has, to a large extent, been avoided. The small risks for therapy depend on where Cyberknife therapy is delivered and is discussed with each patient before the procedure. Radiosurgery has also been established as optimal therapy for some patients with brain metastatic disease (i.e. spread of cancer from other sites in the body to the brain) as well as for some other brain tumours that are too deep in the brain for orthodox surgery – Cyberknife represents finely focussed radiosurgical technology for such problems.
Many of the vascular problems that occur in the brain also occur in the spine and CyberKnife has marked advantages over other radiosurgical techniques in that it is capable of targeting spinal lesions. Thus arteriovenous malformations of the spine are amenable to this radiosurgical technique and some other vascular anomalies that are not encompassing too much of the normal spinal cord. Other spinal cord tumours may be considered for CyberKnife therapy and vertebral tumours (the vertebra is the spine bone) may similarly be treated by this technology (with sparing of the radiosensitive spinal cord that runs through the vertebra). Thus focussed radiation therapy, in single or a few sessions/fractions of therapy, may be successfully employed in cases selected by experts mindful of all the therapeutic options.
Single or several tumours in the lung may be obliterated by single or a few fractions of CyberKnife radiation therapy. Highly focussed obliterative doses of therapy can be used to both kill/ablate individual lung cancers (primary or secondary) with sparing of the surrounding lung (more than other radiotherapeutic techniques). At the same session, the CyberKnife can treat up to several lung tumours notwithstanding the fact that they may be sited in different lung areas (- normal lung sparing from high dose radiation therapy is even more important here, because of the potential cumulative danger from additive radiation normal lung areas). For many patients who are elderly or those who have poor lung function (that makes operative resection risky) or more than one tumour (which the surgeon could not remove at one time) CyberKnife seems the optimal solution.
Since the introduction of PSA screening in men, the discovery of early prostate cancer has greatly increased in the Western world. Importantly, the disease is highly curable at this time; there are a number of treatment options for such patients. Whilst surgery (open or robotic methods) remains popular, it involves a sizeable operation and there are risks of incontinence, impotence and other risks of moderately large surgery. For this reason, other therapy methods have become popular and at least two radiotherapy methods (prostate radiation seed brachytherapy and external beam radiotherapy/IMRT) compete with surgery in terms of success in curing such patients with lesser risks. CyberKnife now offers a third radiotherapeutic method with potential to cure with equal success to IMRT methodology but with far fewer visits to the radiotherapy department for therapy – perhaps five visits versus 38 or more for IMRT. The high degree of focussing of the multiple beams in CyberKnife gives the perceived advantages of highly accurate dose delivery and high dose fractions.
Cancer of the pancreas is a particularly difficult cancer to treat. However, if localised (no evidence of spread to other organs), there is a chance of obliteration. A major operation (Whipple’s operation) is the conventional method; this is a major abdominal operation but gives a chance of cure. Where there are reasons that the patient might not be suitable for this operation, perhaps because the patient is not fit enough to undergo it or the disease seems, on scan, to be particularly difficultly placed – then a highly focussed radiotherapy method may be optimal. The pancreas is surrounded by delicate and radiosensitive structures such as the duodenum and the sophisticated deposition of dose that is effected by CyberKnife allows maximal deposition of radiation dose on the pancreatic tumour and yet sparing of these surrounding organs – in this regard CyberKnife seems advantageous over other radiotherapeutic methods.
Cancer of the liver has been rarely treated by radiotherapy because the normal liver tissue is radiosensitive and harm could come to it if receiving the high dose of radiation necessary to obliterate cancer. Surgery has great merits in treating liver cancer but often the cancer is inoperable – perhaps because the disease is multifocal (so often the case in secondary/metastatic disease in the liver) or because the underlying liver tissue is unhealthy and cannot provide the body with its normal liver function if part was removed (could not compensate for the resected part). Under these circumstances, a focussed radiotherapy method that is able to spare the adjacent liver substance seems to have great merit and Cyberknife perhaps optimally fulfils this role. Cyberknife focuses or targets a high dose of radiotherapy on a liver tumour whilst maximally sparing uninvolved liver. For metastatic cancer, that is not responding to chemotherapy or is too large for other focal methods (e.g. thermoablation), Cyberknife seems the important advance that we have been waiting for, and more than one lesion can be so targeted.
Kidney cancer is treated by removal of the kidney for disease localised to this region. Where the disease has spread, chemotherapy (or nowadays molecularly targeted therapy) is used to control the disease wherever it is. Where that fails to control disease in certain sites, radiotherapy can be extremely useful. However, renal cancer is recognised as being one of the more radioresistant cancers and the need for higher dose therapy is restricted by the dose that surrounding tissues will tolerate. Focussed radiation therapy by CyberKnife can be most useful in these situations. With its high degree of dose deposition accuracy, CyberKnife may be the optimal method of delivering an ablative radiation dose. Treatment is usually delivered in 1-5 fractions.
There are always cancer patients referred into the cancer centre with sites of disease that have escaped orthodox therapy and remain as symptomatic sites of unablated disease. Sometimes, conventional radiotherapy may be sufficient to deal with the problem but, at other times, the tumour is too close to sensitive normal organs for a very high dose to be delivered and it proves to be inoperable for the same reason. Difficult sarcoma problems not infrequently fit into this category and not uncommonly recurrent carcinoma – primary site control problems or those associated with metastatic disease. The use of cyberknife for discrete metastases is perceived to be an important advance. In these situations, Cyberknife gives the advantage of being able to deliver high and highly focussed radiation dosage to these localised cancer problems.
The ability of Cyberknife to focally deposit high doses of ablative radiation on discrete sites of cancer has led to the safer re-treatment of cancers that may have re-grown after previous radiotherapy – as the surrounding normal tissues (almost at tolerance dose to radiation exposure) is spared much of the re-treatment dose.