Impact of CT information on the treatment planning for lung tumors.

With CT information available today, the prevailing, though strong, argument for not applying lung corrections is that all clinical experience gathered so far applies to doses that were prescribed for uniform density throughout the treated volume. To ease the transition from not correcting, to the state of accounting for increased lung transmission, we have planned 10 patients: (a) in the conventional way with a wire contour obtained at simulation; target volume and critical structures were drawn in by the physician utilizing information gathered from diagnostic CT scans and X-ray films; no lung correction was applied for treatment planning. (b) For the same patients, a CT scan was obtained in treatment position and the target volume was outlined on the CT film utilizing the same information as in (a); a relative lung density of 0.3 was assigned for treatment planning. The geometric accuracy of patient outline and target volume obtained in both planning modalities is analyzed, and the intended and actually delivered tumor doses are compared when optimized treatment plans from either planning modality are selected for treatment.