Robotic Radiosurgery with CyberKnife (SBRT) Boost/ Reirradiation, in Cancer, After Standard RadiotherapyWednesday, March 7th, 2012
What is boost therapy?
In general the response to treatment depends on size of the cancer and invisible cancer cells respond best and large cancer respond least. Invisible cells can be eliminated with lesser dose and larger cancers require higher dose. The way of delivering the higher radiation dose to the area of disease visible on CT/PET-CT scan or MRI is considered as “Radiation Boost”. In case of disease recurs in the earlier treated area of radiation, it is important to deliver the highest possible dose to disease visible in CT/PET CT or MRI scan and least possible dose to the normal tissue in the previously irradiated area.
Why CyberKnife Radiosurgery Boost / Reirradiation / Repeat Radiation?
Conventional radiation works by the principle of small doses every day and allow recovery of normal cells in between doses. However, this allows the partial repair of malignant cells also. Therefore, in radiotherapy not only the total dose given but also dose per treatment can affect the tumour control.
When the patient is on the couch during the radiation treatment there will be natural movement of the patient and also that of tumour (due to either breathing or surrounding organ filling with fluid or gas). This may be in terms of few millimetres to few centimetres.
To account for this and not to miss the tumour, wider area of normal tissue is purposefully included. As we include larger normal tissue volume lesser the dose that can be tolerated. Therefore, in conventional radiation therapy focus is more on giving lesser dose to avoid toxicity rather than delivering the required dose to control the tumor.
Additionally, cancers like glioblastomas, renal cell carcinomas, sarcomas and melanomas are considered traditionally difficult to respond to conventional radiation doses.
CyberKnife is the only stereotactic machine, as of now, which tracks the tumour during the treatment and automatically corrects the patient position. This one point has several cascading effects.
Hence, the boost with the Cyberknife is very valuable after conventional radiotherapy. It is also ideal technique to deliver good dose to the tumour in cases of recurrence following earlier radiation.
How CyberKnife radiosurgery (SBRT) does overcome tough cancer cells?
Dose per treatment is higher than the regular radiation and is given in 1 to 5 sittings increasing the probability of killing cancer cells which are no longer responding to regular radiation.
When is CyberKnife boost given?
» After initial radiation therapy of 5 weeks duration.
» After the completion of regular radiotherapy treatment and when the disease is still persisting.
» 3 months after completion of radiotherapy if active disease is still present.
» When the disease comes back in the area treated earlier with radiation.
Sites of cancer that require Cyberknife boost
The common cancer sites that require Cyberknife boost:
» Glioblastoma multioforme and other brain cancers
» Ca. Nasopharynx
» Ca pancreas
» Ca lung
» Cancer in the Head and Neck region
» Others e.g. sarcomas, cancers in the pelvis, including Ca prostate.