Stereotactic radiosurgery in lung cancer
DR.DEBNARAYAN DUTTA, Consultant Radiation Oncologist, Apollo speciality hospital Chennai
Radiosurgery is a non-invasive option in early lung cancer. High dose precise radiosurgery has immense potential. Early data from phase II studies have shown excellent loco-regional control and survival function.
CyberKnife Radiosurgery in lung cancer has following advantages:
1. Cyberknife has the unique technology of ‘see and shoot’. In this technology before each treatment field matching of the target and ‘intra-fraction motion correction’ is done, hence minimal normal lung comes in the radiation field.
2. Cyberknife has sub-millimeter treatment accuracy. Margin (planning target volume) required (where normal lung comes) is minimal around the target. High dose region volume is minimal with Cyberknife and lung toxicity is expected to be lower compared with conventional treatment.
3. Cyberknife has the multiple isocentric technique with non-coplanar field arrangement, hence have unmatched conformity index (uniform dose is delivered). Cyberknife use ‘pencil beam’ with multiple small beamlets delivered from various angles (maximum 1200 different position) hence ‘penumbra’ margin is less.
4. As dosimetry is favorable and total dose delivered with Cyberknife is not higher compared with conventional fraction (usual dose delivered with Cyberknife 60 Gy/3 fr/ 1 week) there is no expected increase in lung toxicity with Cyberknife. Phase II prospective studies with Cyberknife have not shown any increase in radiation induced pneumonitis.
5. ‘STAR trial’ is a multicentric randomized study initiated by MD Anderson Cancer Centre may provide answer to impact of Cyberknife on lung toxicity. There are other few ongoing clinical studies with hypofractionated radiation therapy on lung cancer that will provide useful information in near future
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