Purpose: Whole brain radiotherapy is a widely utilized palliative option for patients with brain metastases. Despite improving overall survival, associated reductions in cognitive function have a significant impact on quality of life. Hippocampal avoidance whole brain radiotherapy can delay the onset of neurocognitive decline. A planning technique published in 2015 demonstrated a class solution by partitioning the brain into sub-volumes and utilizing a VMAT split arc technique. The current study investigates an application of this technique, with simplified sub-volumes, for five clinical cases, with a comparison to alternative modulated techniques.
Methods: Five patients who previously received hippocampal avoidance whole brain radiotherapy were selected for this retrospective planning study. The hippocampal avoidance region (HA) was a 5mm expansion of the hippocampi. The planning target volume (PTV) was the whole brain minus the HA region. The PTV was partitioned into three volumes: superior; mid; and inferior to the HA. Raystation was used to generate plans using the split VMAT technique, VMAT coplanar arcs, VMAT non-coplanar arcs and IMRT. The optimization prioritized dose homogeneity on the superior and inferior volumes. Dose falloff adjacent to the hippocampi was prioritized in the PTV mid-volume. Dose metrics and DVH data were used to assess plan quality. VMAT plans were perturbed in orthogonal directions to assess robustness.
Results: PTV partitioning and standardized optimization parameters were able to meet dosimetric goals. VMAT delivered a more homogenous dose to the brain than IMRT. The VMAT split field was able to provide superior hippocampal avoidance and homogeneity. This technique resulted in the most robust plans under simulated setup variations.
Conclusion: A simple split field VMAT technique consistently produces plans with superior homogeneity and hippocampal sparing. This technique does not require couch rotation and is relatively robust, which results in a simple plan delivery to patients who are often medically compromised.