Background:
Radiotherapy (RT) plays an integral role in the management of low-grade gliomas (LGG). Late toxicity from RT can cause progressive neurocognitive dysfunction. Radiation-induced damage to the hippocampus (HCP) plays a considerable role in memory decline. Advancements in photon planning software have resulted in the development of multi-criteria optimization (MCO) and HyperArc technologies which may improve HCP sparing while maintaining PTV target coverage.

Methods:
Three planning methods for hippocampal sparing (HS) were compared, VMAT without HS (VMAT_noHS), VMAT with HS (VMAT_HS), MCO with HS (VMAT_MCO), and HyperArc with HS (HyperArc_HS).

Results:
25 patients were identified. The contralateral HCP was spared in 16 patients and bilateral HCP in 9 patients with superiorly located tumours. All three HS planning techniques showed significant reductions in dose to the spared HCP in contralateral cases but only VMAT_HS and HyperArc_HS achieved this in bilateral cases (p < 0.008). Only VMAT_MCO was superior to VMAT_HS in lowering the dose to both contralateral HCP and bilateral HCP in all measured metrics (p<0.008). PTV and OAR (organ at risk) dose constraints were achieved for all plans.

Conclusion:
This retrospective dosimetric study demonstrated the feasibility of hippocampal sparing for low-grade glioma. All three HS planning techniques achieved significant dose reductions to the spared contralateral hippocampus, but only MCO_HS and VMAT_HS achieved this in bilateral cases. MCO was superior to other planning techniques for sparing of both bilateral and contralateral hippocampi.