Conventional radiation works on the principle of small doses on a daily basis, allowing the
recovery of normal cells in between these doses. However, this enables the partial repair of
malignant cancer cells also. Therefore, in radiotherapy, the total dose that is provided affect
the tumour control at the rate of a dose-per- treatment. When the patient is on the couch
during radiation treatment, there is bound to be natural movement of the patient and the tumour due to either breathing or the surrounding organ filled with either fluid or gas. This
may vary between a few millimetres to a few centimetres.
To account for this and not to miss the tumour, a wider area of normal tissue is intentionally
included. As we include larger normal tissues, lesser 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 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 destroying 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 mostly in 3-5 days. Now with
technology like CyberKnife, more 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.