Reducing the dosimetric impact of positional errors in field junctions for craniospinal irradiation using VMAT

Area of Science:

• Radiation Oncology
• Medical Physics

Background:

• Craniospinal irradiation (CSI) is complex due to large target volumes requiring overlapping treatment fields.
• Volumetric Modulated Arc Therapy (VMAT) is explored for CSI, offering improved dose distribution and robustness against patient positioning shifts.

Purpose of the Study:

• To enhance the robustness of VMAT treatment plans for CSI against minor patient position shifts.
• To achieve a linear ramp-like dose profile within the overlapping treatment field regions.

Main Methods:

• Developed a VMAT treatment plan with three isocenters for a test case patient.
• Utilized overlapping arc field pairs for cranial and spinal segments.
• Optimized the upper spinal region first, enforcing a ramp-like dose profile, followed by cranial and lower spinal regions.

Main Results:

• Demonstrated that hot/cold spots from field displacement can be reduced by widening overlap regions and minimizing dose gradients.
• Identified a linear ramp as the function with the smallest maximal gradient.
• Presented a technique yielding a desired dose profile, minimizing dosimetric dependence on positional errors.

Conclusions:

• The proposed VMAT planning technique effectively minimizes dosimetric errors caused by patient setup inaccuracies.
• This method improves treatment plan robustness for CSI, particularly in the critical overlapping field regions.