Room: AAPM ePoster Library
Purpose: present a novel technique for delivering craniospinal irradiation (CSI) utilizing Volumetric Modulated Arc Therapy (VMAT) to both reduce treatment setup complexity and improve normal tissue sparing.
Methods: is typically delivered by opposed-lateral cranial fields and one or two spinal fields (upper spine (US) and lower spine (LS)). We developed a new delivery method by replacing each spinal field with two short posterior VMAT arcs with 4cm overlap at each junction. Field-in-field(FIF) technique is used to create a smooth dose fall off at the inferior border of the brain field. The VMAT fields are inverse optimized to get adequate dose coverage in both junctions and conformal dose to the PTV. To ensure a smooth transition in the junction, two planning techniques were investigated: one was an iterative planning approach (iterative-VMAT). We first placed a fixed lower PA spine field with FIF to create a dose fall-off in the junction, and then a VMAT US field was optimized on top of the dose from the fixed PA LS field, finally, a VMAT LS field replaced the fixed field and was optimized on top of the dose from the US field. The second method was to optimize both the US and LS VMAT fields simultaneously (Simultaneous-VMAT). The planning techniques were evaluated with CT images of a humanoid phantom. In addition, film dosimetry was performed for verification.
Results: VMAT planning techniques significantly reduced the dose wash to the normal tissues and hot spot (119% VMAT vs 126% 3D). The film measurement in the junctions showed smooth dose coverage without hot or cold spot with maximum intensity variation <1.5%. The iterative-VMAT technique created a smoother dose fall off ramp for each field than the simultaneous-VMAT technique.
Conclusion: CSI treatment technique provides an efficient way to deliver treatment dose with significantly improved normal tissue sparing.