Three-dimensional treatment planning for central lymphatic irradiation

The purpose of this study was to investigate the applicability of 3-dimensional (3D) treatment planning for central lymphatic irradiation (CLI). CLI requires more than 1 course of treatment with large, highly blocked, overlapping beams, and careful planning is required to ensure that such treatments are delivered safely and effectively. Three patients were selected for this study. Each patient completed at least 1 course of radiation therapy for CLI and was scheduled to receive irradiation to an adjacent area with overlapping beams. Two treatment plans were generated for each patient: a standard, 2-dimensional (2D) treatment plan and a 3D treatment plan designed to mimic the standard plan, taking advantage of unique 3D features. The time required to complete the treatment plans and differences in the treatment planning processes were noted. The time required to generate a 3D treatment plan was approximately the same as the time required to generate a standard 2D treatment plan; however, the 3D planning process required less redundancy of data entry than the 2D process. The 3D treatment plan was qualitatively similar to the standard 2D treatment plan; however, differences in beam penumbra and beam junctions were noted, and are most likely due to differences in the dose-calculation models used in these 2 treatment planning systems. Dose-volume histograms (DVHs) were calculated for the spinal cord and were found to be useful to the physicians for quickly and accurately evaluating the presence or absence of hot spots in the junction region. 3D treatment-planning has some advantages over 2D treatment planning for CLI; the main advantage of the 3D treatment plan is that it provides a single plan for each patient with multiple views of the data, including different planar cross-sections and DVHs. For the 2D system, a separate plan was generated for each view, requiring redundant data entry. The quality of the output of the 3D treatment plans is superior to that of 2D treatment plans, but the clinical utility is about the same. Currently, the time required for 2D and 3D treatment plans is similar. However, as dosimetrists become more familiar with 3D treatment planning systems, we expect this familiarity and regularity of use to translate into a significant time advantage.