ESTRO 2024 - Abstract Book

S3617

Physics - Dose prediction, optimisation and applications of photon and electron planning

ESTRO 2024

1973

Digital Poster

Dose optimized hippocampal-sparing radiosurgery for targets near the skull base

Prateek Mehra 1 , Laura Burgess 1 , Janice Doody 2 , Julia Malone 2 , Eric Vandervoort 2 , Lynn Chang 1 , Vimoj Nair 1 , Jean Michel Caudrelier 1 , Shawn Malone 1 1 The Ottawa Hospital, Division of Radiation Oncology, Ottawa, Canada. 2 The Ottawa Hospital, Cancer Centre, Ottawa, Canada

Purpose/Objective:

Cranial radiation is associated with significant neurocognitive sequelae. 1 The toxicity is in part secondary to radiation-induced damage of the hippocampus. Hippocampal-sparing (HS) leads to modest benefit in neurocognitive function in patients with brain metastases, but further improvement is needed. 2 Stereotactic Radiosurgery (SRS) results in improved neurocognitive function in patients compared to whole brain radiation. 3 We hypothesized that improved benefits could be seen using HS in patients treated with stereotactic radiation (HS-SRS). Our study evaluated whether the hippocampal dose could be significantly reduced in the treatment of SRS targets near the base of skull while maintaining target coverage.

Material/Methods:

39 patients historically treated with radiosurgery for benign targets (e.g. meningiomas, trigeminal neuralgia, acoustic neuromas and arteriovenous malformations) had their baseline SRS plans (in which hippocampal-sparing was not performed) compared to plans aimed to maximize hippocampal sparing. Radiosurgery plans were modified to achieve the lowest hippocampus dose possible while maintaining target coverage. Minimum, mean, maximum and dose to 40% of the hippocampus were compared between SRS and HS-SRS plans. In addition, we evaluated dose to other Organs At Risk (OARs) including brain, brain stem and optic chiasm.

Results:

An overall decrease in the dose to the hippocampus was noted when HS-SRS plans were calculated. Highest dose received by 40% (D 40 ) of the hippocampus was 6986cGy EQD2 at baseline, which decreased to 4381cGy through HS-SRS (p = 0.02). Similarly, there was a significant decrease in the mean dose as well, from 6622cGy to 4402cGy (p < 0.01). The maximum dose also saw a decrease, with baseline plans having a maximum EQD2 of 243423cGy and the HS-SRS plans of 168922cGy (p < 0.01). As far as organs at risk were concerned, there was a minimal change in the average D mean to the whole brain (from 100cGy to 97cGy) and brainstem (from 225cGy to 215cGy). Mean dose to the optic chiasma saw a small increase (from 260cGy to 271cGy).

Conclusion:

Our study demonstrated that there is usually around a 37% decrease in hippocampal D 40 , a 33% decrease in D mean and a 30% decrease in D max when optimising a radiosurgery plan for hippocampal sparing in the treatment of SRS targets near the skull base. This technique could result in significantly improved neurocognitive outcomes for patients treated with SRS.