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Abstract
Background: To identify the pattern of failure and oncological safety of hippocampus (HC)-sparing IMRT (HSRT) in newly diagnosed glioblastoma (GBM) patients.

Materials and methods: Eighty-two GBM patients treated with temozolomide-based chemoradiation using HSRT between 2014 and 2018 were retrospectively reviewed. HSRT consisted of a sparing of Dmax of the contralateral HC < 17 Gy. Fifteen patients were unable to achieve the dose-constraints for adequate target coverage. The dose to ipsilateral HC was kept as low as possible. The pattern of failure was investigated, focusing on the area in the vicinity of the spared HC (organ and + 1 cm area). The median HSRT dose was 60 Gy in 30 fractions.

Results: The median follow-up for survivors was 11.7 months. The median progression-free and overall survival were 9.7 and 23.5 months, respectively. Six (7.3%) and eight (9.8%) patients eventually demonstrated progressive disease at the contralateral HC and HC + 1 cm, respectively. The 12-month contralateral HC and HC + 1 cm failure-free rate were 97.2 and 93.4%, respectively. However, no patient (0%) and two patients (2.4%) showed failure at contralateral HC and HC + 1 cm at initial progression, respectively. The dominant pattern of failure at the contralateral HC was by subependymal seeding (66.7%).

Conclusion: The incidence of failure at the contralateral HC and HC + 1 cm is very low and mostly accompanied by disseminated disease progression after HSRT. Since HSRT does not compromise oncological outcomes, it could be considered especially for GBM patients who are expected to have favorable survival outcomes.

Affiliations

Chan Woo Wee  1 , Kyung Su Kim  1 , Chae-Yong Kim  2 , Jung Ho Han  2 , Yu Jung Kim  3 , In Ah Kim  4   5   6
1 Department of Radiation Oncology, Seoul National University Bundang Hospital, Seongnam-si, Republic of Korea.
2 Department of Neurosurgery, Seoul National University Bundang Hospital, Seongnam-si, Republic of Korea.
3 Department of Internal Medicine, Seoul National University Bundang Hospital, Seongnam-si, Republic of Korea.
4 Department of Radiation Oncology, Seoul National University Bundang Hospital, Seongnam-si, Republic of Korea. inah228@snu.ac.kr.
5 Department of Radiation Oncology, Seoul National University College of Medicine, Seoul, Republic of Korea. inah228@snu.ac.kr.
6 Cancer Research Institute, Seoul National University College of Medicine, Seoul, Republic of Korea. inah228@snu.ac.kr.