Hippocampal sparing in stereotactic radiotherapy for brain metastases: To contour or not contour the hippocampus?

Publication date: Available online 22 March 2018
Source:Cancer/Radiothérapie
Author(s): C. Di Carlo, M. Trignani, L. Caravatta, A. Vinciguerra, A. Augurio, F. Perrotti, M. Di Tommaso, M. Nuzzo, S. Giancaterino, M.D. Falco, D. Genovesi
PurposeThe aim of our study was to evaluate hippocampal irradiation in patients treated with fractionated stereotactic brain radiotherapy.Patients and methodsRetrospective hippocampal dosimetric analysis performed on 22 patients with one to four brain metastases treated with fractionated stereotactic radiotherapy using volumetric intensity-modulated arc therapy. Original plans did not include hippocampus as avoidance structure in optimization criteria; hippocampus was retrospectively delineated on magnetic resonance coregistered with planning CT and using as reference the RTOG 0933 atlas. Hippocampus was defined both as a single and as pair organ. Constraints analysed were: Dmax<16Gy, D40%<7.3Gy, D100%=Dmin<9Gy. Assuming a α/β ratio of 2Gy, biologically equivalent dose in 2Gy fractions was calculated. Hippocampal-sparing plans were developed in cases where hippocampal constraints were not respected in the original plan.ResultsAmong constraints analysed Dmax and D40% have been exceeded in ten out of 22 cases. The constraints were not respected in patients with more than one metastatic lesion and in three patients with only one lesion. Considering all exceeded constraints values in non-hippocampal sparing plans, the 50% of them was respected after replanning. No significant differences were found among conformity and homogeneity index between non-hippocampal sparing and hippocampal sparing plans.ConclusionVolumetric intensity-modulated arc therapy hippocampal sparing plans significantly decreases dose to hippocampus assuring an equal target coverage and organs at risk avoiding.



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