Conventional radiation works on the principle of small doses every day allowing the recovery of normal cells in between doses. However, this enables the partial repair of malignant cancer cells also. Therefore, in radiotherapy, not only is the total dose given but also the dose-per-treatment can affect the tumour control. When the patient is on the couch during radiation treatment, there will be a natural movement of the patient and also the tumour (due to either breathing or the surrounding organ filled with fluid or gas). This may vary between a few millimetres to a few centimetres.
To account for this and to not miss the tumour, a wider area of normal tissue is intentionally included. As we include larger normal tissues, laser doses can be tolerated. Therefore, in conventional radiation therapy for cancer treatment, focus is more on giving lesser doses to avoid toxicity rather than delivering the required dose to control the tumour. When the size of the tumour exceeds 4 centimetres, the conventional radiation schedule may not be as effective as less than 4 centimetres. This is due to the presence of a large number of anoxic cells and resting cancer cells not entering the sensitive phase of the cell cycle during the course of radiation. This results in non-response or/and with recurrence. Also, cancers like renal cell carcinomas, sarcomas and melanomas are considered traditionally resistant to conventional radiation doses.
Conventional radiation therapy (radiotherapy) administers a broad beam of radiation from one or two directions in 30 to 45 treatments. It delivers low-dose beams of radiation over a period of 6-8 weeks, the time required to allow the recovery of healthy tissue damaged during the cancer treatment.
CyberKnife stereotactic radiosurgery for the treatment of cancer delivers high-dose beams of radiation, which can be more effective in killing tumours anywhere in the body. This system can deliver radiation beams from virtually any direction with sub-millimetre accuracy. With CyberKnife radiosurgery, damage to surrounding healthy tissues is minimised; therefore the treatment can be completed typically in 3-5 days. Now with technology like CyberKnife, focused radiation doses are delivered. This increases the chance of the removal of the resistant cancer cells. CyberKnife is the only stereotactic machine, as of now, which tracks the tumour during cancer treatment and automatically corrects the patient’s position.