Room: Exhibit Hall | Forum 4
Purpose: This study investigates potential dosimetric improvements for treating lacrimal gland cancer using an isocentric rotating chair instead of a table top combined with a fixed horizontal ion beam line.Materials and
Methods: Five patients with lacrimal gland cancer previously treated with a horizontal beam line while lying on a flat tabletop were selected for this study. For each patient, coplanar intensity modulated carbon ion therapy plans were redesigned for the patient in a sitting posture. The resulting dose distributions were compared with the clinically accepted plans designed with the patient lying in the traditional supine posture. For each plan, the same number of beam directions were used for the sitting posture plans as the lying posture plans. The sitting posture plans were normalized to give the same PTV dose coverage (VD95%) as clinically accepted ones.
Results: Overall, the sitting posture plans provided better sparing of the brain; mean dose was reduced by 46.1% from 2.08Â±0.41 Gy(RBE) for table plans to 1.12Â±0.54 Gy(RBE) for chair plans (p=0.03). For other OARs such as lens, optical nerve, optical chiasm, eye ball, the improvements were not statistically significant.
Conclusion: This study has demonstrated dosimetric comparison for ion treatment of lacrimal gland cancer between sitting posture with rotating chair and lying posture with table top. For dose coverage of targets and sparing of critical organs close to the target such as lens, optical nerve and chiasm, sitting posture plans shows comparable results to the lying posture plans, meanwhile sitting posture plans shows better sparing for brain tissue. Clinical outcomes of this dosimetric advantages need to be further studied. Future studies will include non-coplanar plans by combining table and chair set-ups and using multiple chair axis tilts.