Room: Exhibit Hall | Forum 5
Purpose: To investigate characteristics and limitations of surface-guided deep inspiration breath-hold(DIBH) radiation therapy for breast cancer.
Methods: The VisionRT system was used for this study.Data from 10 DIBH left-sided breast cancer patients and 10 non-DIBH breast patient were analyzed. AlignRT illustrates real-time patient positioning by comparing a detected surface to the DICOM file imported from TPS as a reference surface.The software shows the difference in position as a â€œdeltaâ€? value in 6 degrees of freedom. MV filming will focus on the vertebral bodies,chestwall and heart alignment.Suggested couch positions using both methods were compared and discrepancies were analyzed with the region of interest delineation, skin rendering discontinuities,TPS auto-contouring threshold settings,patient breathing amplitudes and patient free breathing and breath hold CT scan fusion uncertainties.
Results: We found MV film and VisionRT suggested that couch positions vary under the following conditions: (1)When patient skins have small discontinuous textures,e.g. surgical scars and area marking wires, VisionRT reflects 1~2mm uncertainties. In this case,one should exclude this area in the region of interest;(2)When Eclipse TPS was used to perform auto-contouring the skin surface,VisionRT deltas showed dependence on theEclipse threshold settings. Uncertainties could be as large as 2mm in all directions;(3)2 patients out of this study set showed >3cm breathing amplitude at their chest level(others have average~2cm).These 2 patients had difficult DIBH alignment using the free breathing setup. This problem could have resulted from the inadequate fusion between free breathing and breath-hold scans. Free breathing isocenter is determined by adequate fusion at the treatment level of vertebral body to facilitate DIBH patient treatment. Larger discrepancies were noted in patients with large breathing amplitudes or large body motion.
Conclusion: Adequate CT scan fusions with quality skin rendering contours are important for surface-guided DIBH breast treatment. Inadequate settings could result in up to 2mm patient localization uncertainty.ation uncertainty.
TH- External beam- photons: Motion management (intrafraction)