RESUMO
PURPOSE: Radiation oncologists are rapidly adopting image-guided radiation therapy (IGRT), warranting further evaluation of its role and value. We analyzed the impact of IGRT for one of the most common radiation treatments. METHODS AND MATERIALS: We retrospectively identified patients who received whole-brain radiation therapy (WBRT) with mask immobilization and who underwent routine IGRT with kilovoltage imaging. We calculated IGRT shifts by comparing couch positions before and after imaging. We determined the dosimetric impact of IGRT on lens maximum and dose received by 95% (D95%) of the brain and cribriform region. We calculated episode of care costs using the Medicare Physician Fee Schedule. RESULTS: A total of 206 patients received 2392 image-guided fractions. The median absolute shift was 1 mm, 1 mm, and 2 mm in the vertical, lateral, and longitudinal directions, respectively. Ninety-nine percent of shifts were ≤6 mm, 7 mm, and 9 mm in the vertical, lateral, and longitudinal directions, respectively. For the 22 patients with the largest average shift per fraction, treating without IGRT would have changed D95% brain by a median 3 cGy (interquartile range, 2-9) and D95% cribriform region by a median 39 cGy (interquartile range, 7-116). Without IGRT, lens doses would have increased for 11/22 patients and decreased for 11/22. Using a 700 cGy lens threshold, there was no net change in the proportion of patients above and below the threshold regardless of IGRT use. For a 10-fraction course, daily IGRT accounted for 10% of the total episode of care cost. CONCLUSIONS: IGRT results in small positional corrections during WBRT. Even among cases with the largest shifts, the dosimetric impact is minor for the brain and modest for the cribriform region and lenses. This study suggests mask immobilization alone is sufficient for routine cases, and it may help clinicians make evidence-based decisions about IGRT in this setting.