(Sunday, 7/12/2020) [Eastern Time (GMT-4)]
Room: AAPM ePoster Library
Purpose: evaluate the feasibility of using surface guided DIBH in conjunction with CBCT for target localization in radiation therapy of cancers in the thorax and abdomen.
Methods: patients receiving radiotherapy at our center (two pancreas, two mediastinum, one liver) were investigated in this study. The simulation-CT was acquired with the patients DIBH. The patient surface contour generated from treatment planning system was set as reference for surface guidance. On each treatment day, surface guided DIBH (tolerance of ±3mm and 3°) was used for patient setup, and during CBCT acquisition. The CBCT and simulation-CT were co-registered for target alignment, and patient shifts were calculated. As long as the translational shifts were less than 3mm, the patients were not shifted. If shifts were greater than 3mm, patient was shifted, a new DIBH reference surface was captured and a verification CBCT was done to confirm no further shifts were needed. Then radiation treatment was delivered using DIBH with the newly-captured reference surface.
Results: pancreas and two mediastinum patients were successfully treated using surface guided DIBH with CBCT as target localization. A total of 70 CBCTs, including initial target localization and verification, were acquired over the 56 treatment fractions. Two CBCTs were required due to shifts greater than 3mm for 8 of 56 fractions. A third CBCT was needed due to a second set of shifts needed for 3/56 fractions. One CBCT was all that needed, due to shifts less than 3mm, 45/56 fractions. The one liver patient showed inconsistency and uncorrelated target shifts relative to surface guidance during DIBH, and was re-planned and treated without DIBH.
Conclusion: guided DIBH in conjunction with CBCT for target localization was feasible for four of five patients in this study. For one patient, uncorrelated target and surface shifts were observed.
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