Comparison of intensity-modulated tomotherapy with stereotactically guidedconformal radiotherapy for brain tumors

Purpose: Intensity-modulated radiotherapy (IMRT) offers the potential to mo re closely conform dose distributions to the target, and spare organs at ri sk (OAR). Its clinical value is still being defined. The present study aims to compare IMRT with stereotactically guided conformal radiotherapy (SCRT) for patients with medium size convex-shaped brain tumors. Methods and Materials: Five patients planned with SCRT were replanned with the IMRT-tomotherapy method using the Peacock system (Nomos Corporation). T he planning target volume (PTV) and relevant OAR were assessed, and compare d relative to SCRT plans using dose statistics, dose-volume histograms (DVH ), and the Radiation Therapy Oncology Group (RTOG) stereotactic radiosurger y criteria. Results: The median and mean PTV were 78 cm(3) and 85 cm(3) respectively (r ange 62-119 cm(3)). The differences in PTV doses for the whole group (Peaco ck-SCRT +/-1 SD) were 2% +/- 1.8 (minimum PTV), and 0.1% +/- 1.9 (maximum P TV). The PTV homogeneity achieved by Peacock was 12.1% +/- 1.7 compared to 13.9% +/- 1.3 with SCRT. Using RTOG guidelines, Peacock plans provided acce ptable PTV coverage for all 5/5 plans compared to minor coverage deviations in 4/5 SCRT plans; acceptable homogeneity index for both plans (Peacock = 1.1 vs. SCRT = 1.2); and comparable conformity index (1.4 each). As a conse quence of the transaxial method of are delivery, the optic nerves received mean and maximum doses that were 11.1 to 11.6%, and 10.3 to 15.2% higher re spectively with Peacock plan. The maximum optic lens, and brainstem dose we re 3.1 to 4.8% higher, and 0.6% lower respectively with Peacock plan. Howev er, all doses remained below the tolerance threshold (5 Gy for lens, and 50 Gy for optic nerves) and were clinically acceptable. Conclusions: The Peacock method provided improved PTV coverage, albeit smal l, in this group of convex tumors. Although the OAR doses were higher using the Peacock plans, all doses remained within the clinically defined thresh old and were clinically acceptable. Further improvements may be expected us ing other methods of IMRT planning that do not limit the treatment delivery to transaxial arcs. Each IMRT system needs to be individually assessed as the paradigm utilized may provide different outcomes. (C) 1999 Elsevier Sci ence Inc.