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Scientists discussed the benefit of respiration-gated stereotactic radiotherapy (SRT) for Stage I lung cancer.
"High local control rates have been reported with SRT for Stage I non-small-cell lung cancer. Because high-dose fractions are used, reduction in treatment portals will reduce the risk of toxicity to adjacent structures," researchers in the
"Respiratory gating can allow reduced field sizes and planning four-dimensional computed tomography scans were retrospectively analyzed to study the benefits for gated SRT and identify patients who derive significant benefit from this approach," explained R.W.M. Underberg and colleagues, Vrije University of Amsterdam.
"A total of 31 consecutive patients underwent a four-dimensional computed tomography scan, in which three-dimensional computed tomography data sets for 10 phase bins of the respiratory cycle were acquired during free breathing," the investigators recapped.
"For a total of 34 tumors, the three planning target volumes (PTVs) were analyzed, namely (1) PTV10bins, derived from an internal target volume (ITV) that incorporated all observed mobility (ITV10bins), with the addition of a 3-mm isotropic setup margin; (2) PTVgating, derived from an ITV generated from mobility observed in three consecutive phases ('bins') during tidal-expiration, plus addition of a 3-mm isotropic margin; and (3) PTV10 mm, derived from the addition of a 10-mm isotropic margin to the most central gross tumor volumes in the three bins selected for gating."
"The PTV10bins and PTVgating were, on average, 48.2% and 33.3% of the PTV10 mm, and respective mean volumes of normal tissue (outside the PTV) receiving the prescribed doses were 57.1% and 39.1%, respectively, of that of PTV10 mm. A significant correlation was seen between the extent of tumor mobility (i.e., a three-dimensional mobility vector of at least 1 cm) and reduction in normal tissue irradiation achieved with gating," announced the scientists.
"The ratio of the intersecting and the encompassing volumes of GTVs at extreme phases of tidal respiration predicted for the benefits of gated respiration. The use of 'standard population-based' margins for SRT leads to unnecessary normal tissue irradiation. The risk of toxicity is further reduced if respiration-gated radiotherapy is used to treat mobile tumors."
The researchers concluded, "These findings suggest that gated SRT will be of clinical relevance in selected patients with mobile tumors."
Underberg and colleagues published their study in International Journal of Radiation Oncology Biology Physics (Benefit of respiration-gated stereotactic radiotherapy for stage I lung cancer: an analysis of 4DCT datasets. Int J Radiat Oncol Biol Phys, 2005;62(2):554-560).
For additional information, contact F.J. Lagerwaard, Vrije University of Amsterdam,
Publisher contact information for the International Journal of Radiation Oncology Biology Physics is: Elsevier Science Inc.,