Poster - Thurs Eve-22: Image guided radiation therapy for lung cancer.

Abstract

To determine the geometric accuracy of conventional and stereotactic lung radiotherapy using cone-beam CT image guidance, and assess the efficacy of these image-guided radiation therapy (IGRT) processes. IGRT was first used for our stereotactic lung program, where high geometric accuracy is required to deliver high doses in few fractions. The initial positional accuracy for 47 patients was assessed by registering daily CBCT to the planning CT; the patient position was corrected when the CBCT indicated discrepancies > ± 3 mm in any direction. For 19 of these patients, a second CBCT was acquired to assess the residual error. IGRT was also used to assess the initial and residual errors for lung cancer patients treated conventionally with (14 pts; 584 CBCT) and without (25 pts; 1032 CBCT) a remote-controlled treatment couch. Systematic (Σ) and random (σ) positional errors were assessed for these three groups. For stereotactic lung patients, Σ and σ ranged between 4.1 and 6.1 mm. IGRT reduces these errors to 1.2-1.9 mm, raising the proportion of patients within ± 3 mm from 16% to 82%. For conventional lung cancer patients, Σ and σ ranged between 1.4 and 3.8 mm, and IGRT raises the proportion of patients within ± 3 mm from 27% to 67%, with the remote-controlled couch further improving this proportion to 84%. IGRT clearly confirms the high geometric accuracy required for stereotactic lung patients. This new paradigm has been transported to patients with locally-advanced lung cancer, with similar accuracy.